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Tuesday, August 15, 2023

United States incarceration rate

From Wikipedia, the free encyclopedia
A map of U.S. states by adult incarceration rate per 100,000 adult population, as of December 31, 2013. State prisons and local jails. Excludes federal prisoners.

According to the latest available data at the World Prison Brief on May 7, 2023, the United States has the sixth highest incarceration rate in the world, at 531 people per 100,000. Between 2019 and 2020, the United States saw a significant drop in the total number of incarcerations. State and federal prison and local jail incarcerations dropped by 14% from 2.1 million in 2019 to 1.8 million in mid-2020. In 2018, the United States had the highest incarceration rate in the world.

While the United States represents about 4.2 percent of the world's population, it houses around 20 percent of the world's prisoners. Corrections (which includes prisons, jails, probation, and parole) cost around $74 billion in 2007 according to the U.S. Bureau of Justice Statistics (BJS). According to the Justice Expenditures and Employment in the United States, 2017 report release by BJS, it is estimated that county and municipal governments spent roughly US$30 billion on corrections in 2017.

As of their March 2023 publication, the Prison Policy Initiative, a non-profit organization for decarceration, estimated that in the United States, about 1.9 million people were or are currently incarcerated. Of those who were incarcerated, 1,047,000 people were in state prison, 514,000 in local jails, 209,000 in federal prisons, 36,000 in youth correctional facilities, 34,000 in immigration detention camps, 22,000 in involuntary commitment, 8,000 in territorial prisons, 2,000 in Indian Country jails, and 1,000 in United States military prisons. The data is from various years depending on what is the latest available data.

Prison and jail population

Total incarceration in the United States by year
Total US incarceration peaked in 2008. Total correctional population peaked in 2007.

Total U.S. incarceration (prisons and jails) peaked in 2008. Total correctional population peaked in 2007. If all prisoners are counted (including those juvenile, territorial, U.S. Immigration and Customs Enforcement (ICE) (immigration detention), Indian country, and military), then in 2008 the United States had around 24.7% of the world's 9.8 million prisoners.

In 2009, the United States had the highest documented incarceration rate in the world, at 754 per 100,000. However, following over a decade of decarceration, the prison population had declined from a 2008 peak of 2,307,504 to 1,675,400 (500 per 100,000). This has resulted in a decline to the 6th highest incarceration rate of 505 per 100,000.

This number comprises local jails with a nominal capacity of 907,700 inmates occupied at 60.5%, state prisons with a nominal capacity of 1,121,402 occupied at 86.9%, and federal prisons with a nominal capacity of 134,133 occupied at 112.8%. Of this number, 23.3% are pretrial detainees (2019), 10.2% are female prisoners (2019), 0.2% are juveniles (2019), and 7.3% are foreign prisoners (2019).

The imprisonment rate varies widely by state; Louisiana surpasses this by about 100%, but Maine incarcerates at about a fifth this rate. A report released 28 February 2008, indicates that more than 1 in 100 adults in the United States are in prison.

According to a U.S. Department of Justice report published in 2006, over 7.2 million people were at that time in prison, on probation, or on parole (released from prison with restrictions). That means roughly 1 in every 32 adult Americans are under some sort of criminal justice system control.

Growth and Subsequent Decline

US incarceration count, and rate per 100,000 population. Jails, state prisons, federal prisons.
Year Count Rate
1940 264,834 201
1950 264,620 176
1960 346,015 193
1970 503,586 161
1980 503,586 220
1985 744,208 311
1990 1,148,702 457
1995 1,585,586 592
2000 1,937,482 683
2002 2,033,022 703
2004 2,135,335 725
2006 2,258,792 752
2008 2,307,504 755
2010 2,270,142 731
2012 2,228,424 707
2014 2,217,947 693
2016 2,157,800 666
2018 2,102,400 642
2020 1,675,400 505

In the last quarter of the twentieth century, the incarceration rate in the US increased by a factor of five. Between the years 2001 and 2012, crime rates (both property and violent crimes) have declined 22% after already falling 30% in years prior between 1991 and 2001. In 2012, 710 out of every 100,000 U.S. residents were imprisoned in either local jails, state prisons, federal prisons, and privately operated facilities; close to a quarter of the global prison population.

The Bureau of Justice Statistics has released a study which finds that, despite the total number of prisoners incarcerated for drug-related offenses increasing by 57,000 between 1997 and 2004, the proportion of drug offenders to total prisoners in State prison populations stayed steady at 21%. The percentage of Federal prisoners serving time for drug offenses declined from 63% in 1997 to 55% in that same period. In the twenty-five years since the passage of the Anti-Drug Abuse Act of 1986, the United States penal population rose from around 300,000 to more than two million. Between 1986 and 1991, African-American women's incarceration in state prisons for drug offenses increased by 828 percent.

In 2009, the U.S. Department of Justice announced that the growth rate of the state prison population had fallen to its lowest since 2006, but it still had a 0.2% growth-rate compared to the total U.S. prison population. The California state prison system population fell in 2009, the first year that populations had fallen in 38 years.

When looking at specific populations within the criminal justice system the growth rates are vastly different. In 1977, there were just slightly more than eleven thousand incarcerated women. By 2004, the number of women under state or federal prison had increased by 757 percent, to more than 111,000, and the percentage of women in prison has increased every year, at roughly double the rate of men, since 2000. The rate of incarcerated women has expanded at about 4.6% annually between 1995 and 2005 with women now accounting for 7% of the population in state and federal prisons.

Comparison with other countries

In comparison to countries with similar percentages of immigrants, Germany has an incarceration rate of 67 per 100,000 population (as of June 2022), Italy is 97 per 100,000 (as of November 2022), and Saudi Arabia is 207 per 100,000 (as of 2017). When compared to other countries with a zero tolerance policy for illegal drugs, the rate of Russia is 304 per 100,000 (as of November 2022), Kazakhstan is 184 per 100,000 (as of July 2022), Singapore is 169 per 100,000 (as of December 2021), and Sweden is 74 per 100,000 (as of January 2022).

US timeline graphs of number of people incarcerated in jails and prisons.
The stats source is the World Prison Population List. 8th edition. Prisoners per 100,000 population.

Causes

Felony Sentences in State Courts, study by the United States Department of Justice.
Correctional populations in the United States 1980–2013
2009. Percent of adult males incarcerated by race and ethnicity.

A 2014 report by the National Research Council identified two main causes of the increase in the United States' incarceration rate over the previous 40 years: longer prison sentences and increases in the likelihood of imprisonment. The same report found that longer prison sentences were the main driver of increasing incarceration rates since 1990.

Increased sentencing laws

Even though there are other countries that commit more inmates to prison annually, the fact that the United States keeps their prisoners longer causes the total rate to become higher. To give an example, the average burglary sentence in the United States is 16 months, compared to 5 months in Canada and 7 months in England.

Looking at reasons for imprisonment will further clarify why the incarceration rate and length of sentences are so high. The practice of imposing longer prison sentences on repeat offenders is common in many countries but the three-strikes laws in the U.S. with mandatory 25 year imprisonment — implemented in many states in the 1990s — are statutes enacted by state governments in the United States which mandate state courts to impose harsher sentences on habitual offenders who are previously convicted of two prior serious criminal offenses and then commit a third.

The Violent Crime Control and Law Enforcement Act of 1994 may have had a minor effect on mass incarceration.

Economic and age contributions

Crime rates in low-income areas are much higher than in middle to high class areas. As a result, Incarceration rates in low-income areas are much higher than in wealthier areas due to these high crime rates. When the incarcerated or criminal is a youth, there is a significant impact on the individual and rippling effects on entire communities. Social capital is lost when an individual is incarcerated. How much social capital is lost is hard to accurately estimate, however Aizer and Doyle found a strong positive correlation between lower income as an adult if an individual is incarcerated in their youth in comparison to those who are not incarcerated. 63 percent to 66 percent of those involved in crimes are under the age of thirty. People incarcerated at a younger age lose the capability to invest in themselves and in their communities. Their children and families become susceptible to financial burden preventing them from escaping low-income communities. This contributes to the recurring cycle of poverty that is positively correlated with incarceration. Poverty rates have not been curbed despite steady economic growth. Poverty is not the sole dependent variable for increasing incarceration rates. Incarceration leads to more incarceration by putting families and communities at a dynamic social disadvantage.

Drug sentencing laws

U.S. prisoners (excluding jails) as a percent of the population: male (dashed red), combined (solid black), female (dotted green)

The "War on Drugs" is a policy that was initiated by Richard Nixon with the Comprehensive Drug Abuse Prevention and Control Act of 1970 and vigorously pursued by Ronald Reagan. By 2010, drug offenders in federal prison had increased to 500,000 per year, up from 41,000 in 1985. According to Michelle Alexander, drug related charges accounted for more than half the rise in state prisoners between 1985 and 2000. 31 million people have been arrested on drug related charges, approximately 1 in 10 Americans. In contrast, John Pfaff of Fordham Law School has accused Alexander of exaggerating the influence of the War on Drugs on the rise in the United States' incarceration rate: according to him, the percent of state prisoners whose primary offense was drug-related peaked at 22% in 1990. The Brookings Institution reconciles the differences between Alexander and Pfaff by explaining two ways to look at the prison population as it relates to drug crimes, concluding "The picture is clear: Drug crimes have been the predominant reason for new admissions into state and federal prisons in recent decades" and "rolling back the war on drugs would not, as Pfaff and Urban Institute scholars maintain, totally solve the problem of mass incarceration, but it could help a great deal, by reducing exposure to prison."

As of December 2017, only 14.4% of state prisoners were serving sentences for a drug offenses with 3.7% of serving for possession and 10.8% serving for trafficking, other drug offenses, and unspecified drug offenses. Time served for drug related offenses are also amongst the shortest with prisoners released in 2016 having served an average sentence length 22 months while the median time served only 14 months.

After the passage of Reagan's Anti-Drug Abuse Act in 1986, incarceration for non-violent offenses dramatically increased. The Act imposed the same five-year mandatory sentence on those with convictions involving crack as on those possessing 100 times as much powder cocaine. This had a disproportionate effect on low-level street dealers and users of crack, who were more commonly poor blacks, Latinos, the young, and women.

Courts were given more discretion in sentencing by the Kimbrough v. United States (2007) decision, and the disparity was decreased to 18:1 by the Fair Sentencing Act of 2010.

By 2003, 58% of all women in federal prison were convicted of drug offenses. Black and Hispanic women in particular have been disproportionately affected by the War on Drugs. Since 1986, incarceration rates have risen by 400% for women of all races, while rates for Black women have risen by 800%. Formerly incarcerated Black women are also most negatively impacted by the collateral legal consequences of conviction.

According to the American Civil Liberties Union, "Even when women have minimal or no involvement in the drug trade, they are increasingly caught in the ever-widening net cast by current drug laws, through provisions of the criminal law such as those involving conspiracy, accomplice liability, and constructive possession that expand criminal liability to reach partners, relatives and bystanders."

These new policies also disproportionately affect African-American women. According to Dorothy E. Roberts, the explanation is that poor women, who are disproportionately black, are more likely to be placed under constant supervision by the State in order to receive social services. They are then more likely to be caught by officials who are instructed to look specifically for drug offenses. Roberts argues that the criminal justice system's creation of new crimes has a direct effect on the number of women, especially black women, who then become incarcerated.

Racialization

One of the first laws in the U.S. against drugs was the Smoking Opium Exclusion Act of 1909. It prohibited the smoking of opium, which was ingested but not smoked by a substantial portion of Caucasian housewives in America. It was smoked mainly by Asian American immigrants coming to build the railroads. These immigrants were targeted with anti-Asian sentiment, as many voters believed they were losing jobs to Asian immigrants.

Disproportional incarceration of black people

Currently, the U.S. is at its highest rate of imprisonment in history, with young Black men experiencing the highest levels of incarceration. One out of every 15 people imprisoned across the world is a Black American incarcerated in the United States. A 2004 study reported that the majority of people sentenced to prison in the United States are Black, and almost one-third of Black men in their twenties are either on parole, on probation, or in prison. These disproportionate levels of imprisonment have made incarceration a normalized occurrence for African-American communities. This has caused a distrust from Black individuals towards aspects of the legal system such as police, courts, and heavy sentences. In 2011, more than 580,000 Black men and women were in state or federal prison. Black men and women are imprisoned at higher rates compared to all other age groups, with the highest rate being Black men aged 25 to 39. In 2001, almost 17% of Black men had previously been imprisoned in comparison to 2.6% of White men. By the end of 2002, of the two million inmates of the U.S. incarceration system, Black men surpassed the number of White men (586,700 to 436,800 respectively of inmates with sentences more than one year). In the same year, there were also more Black women behind bars than White women (36,000 to 35,400). African-Americans are about eight times more likely to be imprisoned than Whites. The Sentencing Project, a Washington, D.C.-based non-profit organization, released in 1990 that almost one in four Black men in the U.S. between the ages of 20 and 29 were under some degree of control by the criminal justice system. In 1995, the organization announced that the rate had increased to one in three. In the same year, the non-profit stated that more than half of young Black men were then under criminal supervision in both D.C. and Baltimore. In addition, African-American women are the largest growing incarcerated population.

The War on Drugs plays a role in the disproportionate amount of incarcerated African-Americans. Despite a general decline in crime, the massive increase in new inmates due to drug offenses ensured historically high incarceration rates during the 1990s and beyond, with New York City serving as an example. Drug-related arrests continued to increase in the city despite a near 50% drop in felony crimes. While White individuals have a higher rate of drug use, 60% of people imprisoned for drug charges in 1998 were Black. Drug crimes constituted 27% of the increase in the number of Black state prisoners in the 1990s, while Whites experienced a 14% increase. The rise in African-American imprisonment as a result of newer drug crimes has been justified for its alleged societal benefits. Law officials and advocates of these policies argue that targeting underserved, primarily inner-city neighborhoods is appropriate because these areas see the more harmful and violent effects of drug use. These same individuals further point to the negative effects drug distribution has on these areas to support the inequity in how crimes involving, for example, powdered cocaine can be treated with less severity than crack cocaine. This ideology results in a greater number of arrests of poor, inner-city Black individuals.

A significant contributing factor to these figures are the racially and economically segregated neighborhoods that account for the majority of the Black prison population. These neighborhoods are normally impoverished and possess a high minority population. For example, as many as one in eight adult males who inhabit these urban areas is sent to prison each year, and one in four of these men is in prison on any given day. A 1992 study revealed that 72% of all New York State's prisoners came from only 7 of New York City's 55 community districts. Many recently released individuals return to the area they lived in prior to incarceration. Also in New York City, rates of incarceration stayed the same or grew in 1996 in neighborhoods that had the highest rates in 1990. Additionally, in these same neighborhoods, there was a stronger police presence and parole surveillance despite a period of a general decline in crime.

Finding employment post-release is a significant struggle for African-Americans. American sociologist Devah Pager performed a study to prove this. She assembled pairs of fake job seekers to find jobs with résumés that portrayed the applicant had a criminal record. The findings indicated that the presence of a criminal record reduced callbacks by approximately 50%. This was more common for African-Americans than for Whites.

Prison privatization

In the 1980s, the rising number of people incarcerated as a result of the War on Drugs and the wave of privatization that occurred under the Reagan Administration saw the emergence of the for-profit prison industry. Although modern private prisons did not exist in the US prior to the 1980s, the concept of private prisons can be found within the United States as early as the 1800s. In 1844, Louisiana privatized its penitentiary when it allowed a private company to run the facility as a factory where prisoners were used to manufacture clothing.

In a 2011 report by the ACLU, it is claimed that the rise of the for-profit prison industry is a "major contributor" to "mass incarceration," along with bloated state budgets. Louisiana, for example, has the highest rate of incarceration in the world with the majority of its prisoners being housed in privatized, for-profit facilities. Such institutions could face bankruptcy without a steady influx of prisoners. A 2013 Bloomberg report states that in the past decade the number of inmates in for-profit prisons throughout the U.S. rose 44 percent.

Corporations who operate prisons, such as CoreCivic (formerly the Corrections Corporation of America) and The GEO Group, spend significant amounts of money lobbying the federal government along with state governments. The two aforementioned companies, the largest in the industry, have been contributors to the American Legislative Exchange Council (ALEC), which seeks to expand the privatization of corrections and lobbies for policies that would increase incarceration, such as three-strike laws and "truth-in-sentencing" legislation. Prison companies also sign contracts with states that guarantee at least 90 percent of prison beds be filled. If these "lockup quotas" aren't met, the state must reimburse the prison company for the unused beds. Prison companies use the profits to expand and put pressure on lawmakers to incarcerate a certain number of people. This influence on the government by the private prison industry has been referred to as the Prison–industrial complex.

The industry is well aware of what reduced crime rates could mean to their bottom line. This from the CCA's SEC report in 2010:

Our growth … depends on a number of factors we cannot control, including crime rates … [R]eductions in crime rates … could lead to reductions in arrests, convictions and sentences requiring incarceration at correctional facilities.

In January 2021, U.S. President Joe Biden signed an executive order directing the Department of Justice (DOJ) to begin phasing out its contracts with private federal prisons.

As of March 2021, the private prison population of the United States has seen a 16% decline since reaching its peak in 2012 with 137,000 people incarcerated. According to a March 2021 report released by The Sentencing Project, 115,428 people were incarcerated in private prisons in the US, representing 8% of the total state and federal prison population.

Editorial policies of major media

Gallup polling since 1989 has found that in most years in which there was a decline in the U.S. crime rate, a majority of Americans said that violent crime was getting worse.

A substantial body of research claims that incarceration rates are primarily a function of media editorial policies, largely unrelated to the actual crime rate. Constructing Crime: Perspectives on Making News and Social Problems is a book collecting together papers on this theme. The researchers say that the jump in incarceration rate from 0.1% to 0.5% of the United States population from 1975 to 2000 (documented in the figure above) was driven by changes in the editorial policies of the mainstream commercial media and is unrelated to any actual changes in crime. Media consolidation reduced competition on content. That allowed media company executives to maintain substantially the same audience while slashing budgets for investigative journalism and filling the space from the police blotter, which tended to increase and stabilize advertising revenue. It is safer, easier and cheaper to write about crimes committed by poor people than the wealthy. Poor people can be libeled with impunity, but major advertisers can materially impact the profitability of a commercial media organization by reducing their purchases of advertising space with that organization.

News media thrive on feeding frenzies (such as missing white women) because they tend to reduce production costs while simultaneously building an audience interested in the latest development in a particular story. It takes a long time for a reporter to learn enough to write intelligently about a specific issue. Once a reporter has achieved that level of knowledge, it is easier to write subsequent stories. However, major advertisers have been known to spend their advertising budgets through different channels when they dislike the editorial policies. Therefore, a media feeding frenzy focusing on an issue of concern to an advertiser may reduce revenue and profits.

Sacco described how "competing news organizations responded to each other's coverage [while] the police, in their role as gatekeepers of crime news, reacted to the increased media interest by making available more stories that reflected and reinforced" a particular theme. "[T]he dynamics of competitive journalism created a media feeding frenzy that found news workers 'snatching at shocking numbers' and 'smothering reports of stable or decreasing use under more ominous headlines.'"

The reasons cited above for increased incarcerations (US racial demographics, Increased sentencing laws, and Drug sentencing laws) have been described as consequences of the shift in editorial policies of the mainstream media.

Additionally, media coverage has been proven to have a profound impact on criminal sentencing. Beale found that the more media attention a criminal case is given, the greater the incentive for prosecutors and judges to pursue harsher sentences. This is directly linked to the enormous increase in media coverage of crime over the past two decades. While crime decreased by 8% between 1992 and 2002, news reports on crime increased by 800% and the average prison sentence length increased by 2,000% for all crimes. Less media coverage means a greater chance of a lighter sentence or that the defendant may avoid prison time entirely.

Citizenship statistics

Inmate citizenship statistics, which are updated monthly by the Federal Bureau of Prisons, lists the following statistics for July 2021: 83.67% of Federal inmates are U.S. citizens; 9.3% are citizens of Mexico, and the next three countries—Colombia, Cuba, and the Dominican Republic, contribute less than 1% each; 4.9% have other or unknown citizenship. The Bureau did not state how many had come to the U.S. legally.

Suicide among LGBT youth

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Suicide_among_LGBT_youth

Research has found that attempted suicide rates and suicidal ideation among lesbian, gay, bisexual, transgender (LGBT) youth are significantly higher than among the general population.

In the United States, one study has shown the passage of laws that discriminate against LGBT people may have significant negative impacts on the physical and mental health and well-being of LGBT youth; for example, depression and drug use among LGBT people have been shown to increase significantly after the passage of discriminatory laws. By contrast, the passage of laws that recognize LGBT people as equal with regard to civil rights, such as laws supporting same-sex marriage, may have significant positive impacts on the physical and mental health and well-being of LGBT youth.

Bullying of LGBT youth is a contributing factor in many suicides, even if not all of the attacks have been specifically regarding sexuality or gender. Since a series of suicides in the early 2000s, more attention has been focused on the issues and underlying causes in an effort to reduce suicides among LGBT youth. Research by the Family Acceptance Project has demonstrated that "parental acceptance, and even neutrality, with regard to a child's sexual orientation" can bring down the attempted suicide rate.

Reports and studies

Clinical social worker Caitlin Ryan's Family Acceptance Project (San Francisco State University) conducted the first study of the effect of family acceptance and rejection on the health, mental health, and well-being of LGBT youth, including suicide, HIV/AIDS, and homelessness. Their research shows that LGBT youths "who experience high levels of rejection from their families during adolescence (when compared with those young people who experienced little or no rejection from parents and caregivers) were more than eight times [more] likely to have attempted suicide, more than six times likely to report high levels of depression, more than three times likely to use illegal drugs, and more than three times likely to be at high risk for HIV or other STDs" by the time they reach their early 20s.

Numerous studies have shown that lesbian, gay, and bisexual youth have a higher rate of suicide attempts than do heterosexual youth. According to a Trevor Project 2023 survey, 18% of LGBT youth have attempted suicide, a rate 2 times higher than teenaged general population. This higher prevalence of suicidal ideation and overall mental health problems among gay teenagers compared to their heterosexual peers has been attributed to minority stress, bullying, and parental disapproval.

Parents with higher levels of education or belonging to different ethnicities do not seem to provide significant impact on LGBT+ suicide statistics.

In terms of school climate, "approximately 25 percent of lesbian, gay and bisexual students and university employees have been harassed due to their sexual orientation, as well as a third of those who identify as transgender, according to the study and reported by the Chronicle of Higher Education." Research has found the presence of gay–straight alliances (GSAs) in schools is associated with decreased suicide attempts; in a study of LGBT youth, ages 13–22, 16.9% of youth who attended schools with GSAs attempted suicide versus 33.1% of students who attended schools without GSAs.

"LGBT students are three times as likely as non-LGBT students to say that they do not feel safe at school (22% vs. 7%) and 90% of LGBT students (vs. 62% of non-LGBT teens) have been harassed or assaulted during the past year."

An international study found that suicidal LGBT people showed important differences with suicidal heterosexuals, in a matched-pairs study. That study found suicidal LGBT people were more likely to communicate suicidal intentions, to search for new friends online, and to find more support online than did suicidal heterosexuals.

The black transgender and gender non-conforming community has been found to face discrimination to a higher degree than the rest of the transgender community, which is due to the intersection of racism and transphobia. Research has found that this community experiences a higher level of poverty, suicide attempts, and harassment, while the effects of HIV and being refused health care due to transphobia and/or racism are greater as well.

A survey by the National LGBTQ task force found that amongst the black respondents 49% reported having attempted suicide. Additional findings were that this group reported that 26% are unemployed and 34% reported an annual income of less than $10,000 per year. 41% of respondents reported homelessness at some point in their lives, which is more than five times the rate of the general US population. Also, the report revealed that the black transgender or gender non-conforming community reported 20.23% were living with HIV and that half of the respondents who attended school expressing a transgender identity or gender non-conformity reported facing harassment. 27% of black transgender youth reported being physically assaulted, 15% were sexually assaulted and 21% left school due to these instances of harassment.

A more recent survey by The Trevor Project revealed that 21% of African American LGBT youth have attempted suicide throughout 2021. Amongst Native American youth, 31% of LGBT youth have attempted suicide, and amongst Latin American youth, 18% of survey respondents admitted they have attempted suicide in the past year.

A 2022 study found that the use of gender-affirming hormone therapy in transgender and nonbinary youth was associated with a significant decrease in depression and suicidality.

Familial acceptance

Familial responses to LGBT youth identities differ from person to person. They range from acceptance to outright rejection of the LGBT individual. "Family connectedness" is important in an LGBT youth's life because it will help establish a positive mental health. One of the negative outcomes of LGBT youth confiding in family members about their sexual identities is the risk of being kicked out of their homes. When these youth do not have the support and acceptance of their family, they are more likely to turn to other riskier sources.

Amongst transgender youth, these effects are even more pronounced. In a sample of 84 transgender youth, those that reported being strongly supported by their parents, had a 93% lower suicide attempt rate (a 14-fold difference). In a separate survey of nearly 34,000 LGBT youth, those with supportive families reported a suicide attempt rate that was less than half of those without supportive families.

Impact of same-sex marriage

Across OECD countries, the legalisation of same-sex marriage is associated with reductions in the suicide rate of youth aged 10–24, with this association persisting into the medium term. The establishment of the legal right of same-sex marriage in the United States is associated with a significant reduction in the rate of attempted suicide among children, with the effect concentrated among children of a minority sexual orientation.

A study of nationwide data from across the United States from January 1999 to December 2015 revealed that the recognition of same-sex marriage is associated with a significant reduction in the rate of attempted suicide among children, with the effect being concentrated among children of a minority sexual orientation (LGBT youth), resulting in approximately 134,000 fewer children attempting suicide each year in the United States. Comparable findings are observed outside the United States. A study using cross-country data from 1991 to 2017 for 36 OECD countries found that same-sex marriage legalization is associated with a decline in youth suicide of 1.191 deaths per 100,000 youth, with this reduction persisting at least into the medium term.

OECD countries

A study of country-level data across 36 OECD countries from 1991 to 2017 found that same-sex marriage legalization reduced the suicide rate of youth aged 10–24 by 1.191 deaths per 100,000 youth, equal to a 17.90% decrease. This decline was most pronounced in males for whom the suicide rate fell by 1.993 compared to a decrease of 0.348 for female youth, corresponding to decreases of 19.98% and 10.90%, respectively. The study worked by exploiting common factors in the youth suicide rate across time between the sample countries to econometrically estimate what the suicide rate would have been in the absence of same-sex marriage legalization for the countries and years that same-sex marriage was legal. The impact of same-sex marriage legalization could then be inferred by comparing this estimated counterfactual to the observed data across time, thereby enabling inferences to be interpreted causally. By virtue of this design, the researchers were able to establish that the association persisted at least into the medium term and that countries that recently adopted same-sex marriage (the Netherlands was the first country to legalize same-sex marriage in 2001 and, as of 2017, 18 of the 36 sample countries had followed suit) also experienced declines in youth suicide. These findings indicate that future legalization in other developed countries would also engender a decrease in youth suicide over time.

United States

A study of nationwide data from January 1999 to December 2015 revealed an association between states that established same-sex marriage and reduced rates of attempted suicide among all schoolchildren in grades 9–12, with a rate reduction in all schoolchildren (LGB and non-LGB youth) in grades 9–12 declining by 7% and a rate reduction among schoolchildren of a minority sexual orientation (LGB youth) in grades 9–12 of 14%, resulting in approximately 134,000 fewer children attempting suicide each year in the United States. The gradual manner in which same-sex marriage was established in the United States (expanding from 1 state in 2004 to all 50 states in 2015) allowed the researchers to compare the rate of attempted suicide among children in each state over the time period studied. Once same-sex marriage was established in a particular state, the reduction in the rate of attempted suicide among children in that state became permanent. No reduction in the rate of attempted suicide among children occurred in a particular state until that state recognized same-sex marriage. The lead researcher of the study observed that "laws that have the greatest impact on gay adults may make gay kids feel more hopeful for the future".

Other research shows that while this nationwide study has shown an association between states that established same-sex marriage and reduced rates of attempted suicide among all schoolchildren in grades 9–12, it does not show causation. According to Julie Cerel, director of the Suicide Prevention & Exposure Lab at the University of Kentucky, LGBTQ children "experience much more interpersonal stress from schools, from peers and from home". The Centers for Disease Control and Prevention survey found that more than 1 in 5 young adults (22%) attempted suicide in 2021. Stigma and violence against LGBTQ teens has greatly contributed to their mental health.

Developmental psychology perspectives

The diathesis-stress model suggests that biological vulnerabilities predispose individuals to different conditions such as cancer, heart disease, and mental health conditions like major depression, a risk factor for suicide. Varying amounts of environmental stress increase the probability that these individuals will develop that condition. Minority stress theory suggests that minority status leads to increased discrimination from the social environment which leads to greater stress and health problems. In the presence of poor emotion regulation skills this can lead to poor mental health. Also, the differential susceptibility hypothesis suggests that for some individuals their physical and mental development is highly dependent on their environment in a "for-better-and-for-worse" fashion. That is, individuals who are highly susceptible will have better than average health in highly supportive environments and significantly worse than average health in hostile, violent environments. The model can help explain the unique health problems affecting LGBT populations including increased suicide attempts. For adolescents, the most relevant environments are the family, neighborhood, and school. Adolescent bullying – which is highly prevalent among sexual minority youths – is a chronic stressor that can increase risk for suicide via the diathesis-stress model. In a 2011 study of American lesbian, gay, and bisexual adolescents, Mark Hatzenbuehler found that a more conservative social environment elevated risk in suicidal behavior among all youth and that this effect was stronger for LGB youth. Furthermore, he found that the social environment partially mediated the relation between LGB status and suicidal behaviour. Hatzenbuehler found that even after such social as well as individual factors were controlled for, however, that "LGB status remained a significant predictor of suicide attempts."

Institutionalized and internalized homophobia

Institutionalized and internalized homophobia may also lead LGBT youth to not accept themselves and have deep internal conflicts about their sexual orientation. Parents may abandon or force children out of home after the child's coming out.

Homophobia arrived at by any means can be a gateway to bullying which can take many forms. Physical bullying is kicking, punching, while emotional bullying is name calling, spreading rumors and other verbal abuse. Cyber bullying involves abusive text messages or messages of the same nature on Facebook, Twitter, also social media networks. Sexual bullying includes inappropriate touching, lewd gestures or jokes.

Bullying may be considered a "rite of passage", but studies have shown it has negative physical and psychological effects. "Sexual minority youth, or teens that identify themselves as gay, lesbian or bisexual, are bullied two to three times more than heterosexuals", and "almost all transgender students have been verbally harassed (e.g., called names or threatened in the past year at school because of their sexual orientation (89%) and gender expression (89%)") according to Gay, Lesbian and Straight Education Network's Harsh Realities: The Experiences of Transgender Youth In Our Nation's Schools.

Projects

Several NGOs have started initiatives to attempt a reduction of LGBT youth suicides, such as The Trevor Project and the It Gets Better Project. Actions such as Ally Week, Day of Silence, and Suicide intervention have helped to combat both Self-harm and violence against LGBT people.

Policy responses

A number of policy options have been repeatedly proposed to address this issue. Some advocate intervention at the stage in which youth are already suicidal (such as crisis hotlines), while others advocate programs directed at increasing LGBT youth access to factors found to be "protective" against suicide (such as social support networks or mentors).

One proposed option is to provide LGBT-sensitivity and anti-bullying training to current middle and high school counselors and teachers. Citing a study by Jordan et al., school psychologist Anastasia Hansen notes that hearing teachers make homophobic remarks or fail to intervene when students make such remarks are both positively correlated with negative feelings about an LGBT identity. Conversely, a number of researchers have found the presence of LGBT-supportive school staff to be related to "positive outcomes for LGBT youth". Citing a 2006 Psychology in the Schools report, The Trevor Project notes that "lesbian, gay, bisexual, transgender and questioning (LGBTQ) youth who believe they have just one school staff member with whom they can talk about problems are only 1/3 as likely as those without that support to... report making multiple suicide attempts in the past year."

Another frequently proposed policy option involves providing grant incentives for schools to create and/or support Gay–Straight Alliances, student groups dedicated to providing a social support network for LGBT students. Kosciw and Diaz, researchers for the Gay, Lesbian and Straight Education Network, found in a nationwide survey that "students in schools with a GSA were less likely to feel unsafe, less likely to miss school, and more likely to feel that they belonged at their school than students in schools with no such clubs." Studies have shown that social isolation and marginalization at school are psychologically damaging to LGBT students, and that GSAs and other similar peer-support group can be effective providers of this "psychosocial support".

Early interventions for LGBT youth

Be proactive and understanding

Educators can be proactive in helping adolescents with gender identity and the questions/issues that sometimes come with them. Normalizing education about sexualities and genders can help prevent adolescents from resorting to suicide, drug abuse, homelessness, and many more psychological problems. Van Wormer & McKinney (2003) relate that understanding LGBT students is the first step to suicide prevention. They use a harm reduction approach, which meets students where they are to reduce any continued harm linked with their behaviors. They relate that creating a supportive and culturally diverse environment is crucial to social acceptance in an educational setting.

LGBT role models/resources

It could be beneficial to hire LGBT teachers to serve as role models and support LGBT students. Many of the resources in the U.S. are crisis-driven- not prevention-driven. In order to prevent suicide for LGBT adolescents, it needs to be the other way around. Furthermore, studies show that counselors and teachers need to be trained in self-awareness, sexuality and sexual diversity with themselves and with students. Researchers also suggest inviting gay/lesbian and bisexual panels from colleges or universities to conduct classroom discussions. Education and resources is potentially key to helping LGBT students and families. According to researcher Rob Cover, role models and resources benefit LGBT youth only if they avoid replicating stereotypes and provide diverse visual and narrative representations to allow broad identification.

Having a PFLAG (Parents Families, and Friends of Lesbians and Gays) and GSA Club are possible resources to promote discussions and leadership roles to LGBT students. These resources extend outside of school and in the community. (Greytak, E. A., Kosciw, J. G., & Boesen, M. J. 2013) report that when schools have a GSA or Gay Straight Alliance club or a club promoting social awareness and camaraderie of sorts, supportive educators, inclusive curricula, and comprehensive policies that LGBT students were victimized less and had more positive school experiences. This would allow LGBT students to be positive and want to be in school.

Teach tolerance and examine a school's climate

Examine a school's climate and teach tolerance – Teaching Tolerance is a movement, magazine and website which gives many tools and ideas to help people be tolerant of one another. It demonstrates that the classroom is a reflection of the world around us. Educators can use Teach Tolerance's website and book to download resources and look up creative ways to learn more about LGBT students and teaching tolerance to their students in the classroom. It helps schools get started with anti-bullying training and professional development and resource suggestions. It even relates common roadblocks and tips to starting a GSA club.

Research shows that a collaborative effort must be made in order to prevent LGBT students from being bullied and/or committing suicide. Teachers, administrators, students, families, and communities need to come together to help LGBT students be confident. Each school has its own individuality, its own sense of "self", whether it be the teachers, administrators, students, or the surrounding community. In order to tackle the issue of bullying for LGBT students it needs to start with understanding the student population and demographic where the school lies. Educating students, faculty, staff, and school boards on LGBT issues and eliminating homophobia and transphobia in schools, training staff on diversity acceptance and bullying prevention, and implementing Gay–Straight Alliances is key to suicide prevention for LGBT students (Bacon, Laura Ann 2011). Adolescents grow and are shaped by many factors including internal and external features (Swearer, Espelage, Vaillancourt, & Hymel, 2010).

The school climate must foster respect. Thus, setting the tone for administration, teachers, professionals who enter the building, parents and most importantly the students. People, in general, need to understand their own misconceptions and stereotypes of what being LGBT is. Unless students and adults are educated on the LGBT community, than stereotypes and negative attitudes will continue to exist (Knotts, G., & Gregorio, D. 2011). The GMCLA (Gay Men's Chorus of Los Angeles) use music and singing as a vehicle for changing the attitudes and hearts of people in schools nationwide. Their goal is to bring music to standards-driven curriculum to youth with the purpose of teaching content in innovative and meaningful ways. They instill in students and staff techniques to foster positive meaning of the social and personal issues dealt with in school and society.

Gay, L. (2009) has generated a guide to helping school safety/climate and fostering positive interpersonal relationships through "The Safe Space Kit". This tool helps teachers create a safe space for LGBT students. One of the most effective ways for an educator to create a safe space is to be a supportive ally to LGBT students. This kit has numerous tools for teachers and schools to utilize to help transgender youth, including: a hard copy of "The Safe Space Kit" includes the "Guide to Being an Ally", stickers and two Safe Space posters. Even utilizing something just to promote awareness, such as using "The Safe Space Kit" could be a good first step for schools to promote responsiveness to LGBT students. Providing some supports rather than none at all can benefit LGBT youth tremendously now and in the future (Greytak, et al. 2013).

OBPP (Olweus Bullying Prevention Program)

OBPP is an anti-bullying program designed by psychologist Dan Olweus utilized in schools in Europe, Canada and the U.S. Reductions in bullying were due to parent training, playground supervision, home-school communication, classroom rules, and training videos. Furthermore, Swearer, et al. (2010) discuss a "dosage effect" in which the more positive and consistent elements included in a program, the more the likelihood that bullying would decrease. Success in one school does not guarantee success in another because each school has its own social climate. The OBPP is effective but still needs to be analyzed further, since there are many things to consider when implementing this technique within a large school.

Steps To Respect

Steps To Respect is an anti-bullying campaign which can be beneficial in schools as well – it is a comprehensive guide for teachers, administrators, and students utilizing in class lessons and training helping schools foster positive social-emotional skills and conflict resolution. If schools are able to change peer conduct and norms, increase student communication skills, and maintain adult prevention and intervention efforts, the positive effects of their work will strengthen over time (Frey, Edstrom & Hirschstein 2005) and continue to grow as each class progresses through the school system.

Photoluminescence

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Photoluminescence
Fluorescent solutions under UV light. Absorbed photons are rapidly re-emitted under longer electromagnetic wavelengths.

Photoluminescence (abbreviated as PL) is light emission from any form of matter after the absorption of photons (electromagnetic radiation). It is one of many forms of luminescence (light emission) and is initiated by photoexcitation (i.e. photons that excite electrons to a higher energy level in an atom), hence the prefix photo-. Following excitation, various relaxation processes typically occur in which other photons are re-radiated. Time periods between absorption and emission may vary: ranging from short femtosecond-regime for emission involving free-carrier plasma in inorganic semiconductors up to milliseconds for phosphoresence processes in molecular systems; and under special circumstances delay of emission may even span to minutes or hours.

Observation of photoluminescence at a certain energy can be viewed as an indication that an electron populated an excited state associated with this transition energy.

While this is generally true in atoms and similar systems, correlations and other more complex phenomena also act as sources for photoluminescence in many-body systems such as semiconductors. A theoretical approach to handle this is given by the semiconductor luminescence equations.

Forms

Schematic for the excitation-relaxation processes of photoluminescence

Photoluminescence processes can be classified by various parameters such as the energy of the exciting photon with respect to the emission. Resonant excitation describes a situation in which photons of a particular wavelength are absorbed and equivalent photons are very rapidly re-emitted. This is often referred to as resonance fluorescence. For materials in solution or in the gas phase, this process involves electrons but no significant internal energy transitions involving molecular features of the chemical substance between absorption and emission. In crystalline inorganic semiconductors where an electronic band structure is formed, secondary emission can be more complicated as events may contain both coherent contributions such as resonant Rayleigh scattering where a fixed phase relation with the driving light field is maintained (i.e. energetically elastic processes where no losses are involved), and incoherent contributions (or inelastic modes where some energy channels into an auxiliary loss mode),

The latter originate, e.g., from the radiative recombination of excitons, Coulomb-bound electron-hole pair states in solids. Resonance fluorescence may also show significant quantum optical correlations.

More processes may occur when a substance undergoes internal energy transitions before re-emitting the energy from the absorption event. Electrons change energy states by either resonantly gaining energy from absorption of a photon or losing energy by emitting photons. In chemistry-related disciplines, one often distinguishes between fluorescence and phosphorescence. The former is typically a fast process, yet some amount of the original energy is dissipated so that re-emitted light photons will have lower energy than did the absorbed excitation photons. The re-emitted photon in this case is said to be red shifted, referring to the reduced energy it carries following this loss (as the Jablonski diagram shows). For phosphorescence, electrons which absorbed photons, undergo intersystem crossing where they enter into a state with altered spin multiplicity (see term symbol), usually a triplet state. Once the excited electron is transferred into this triplet state, electron transition (relaxation) back to the lower singlet state energies is quantum mechanically forbidden, meaning that it happens much more slowly than other transitions. The result is a slow process of radiative transition back to the singlet state, sometimes lasting minutes or hours. This is the basis for "glow in the dark" substances.

Photoluminescence is an important technique for measuring the purity and crystalline quality of semiconductors such as GaN and InP and for quantification of the amount of disorder present in a system.

Time-resolved photoluminescence (TRPL) is a method where the sample is excited with a light pulse and then the decay in photoluminescence with respect to time is measured. This technique is useful for measuring the minority carrier lifetime of III-V semiconductors like gallium arsenide (GaAs).

Photoluminescence properties of direct-gap semiconductors

In a typical PL experiment, a semiconductor is excited with a light-source that provides photons with an energy larger than the bandgap energy. The incoming light excites a polarization that can be described with the semiconductor Bloch equations. Once the photons are absorbed, electrons and holes are formed with finite momenta in the conduction and valence bands, respectively. The excitations then undergo energy and momentum relaxation towards the band-gap minimum. Typical mechanisms are Coulomb scattering and the interaction with phonons. Finally, the electrons recombine with holes under emission of photons.

Ideal, defect-free semiconductors are many-body systems where the interactions of charge-carriers and lattice vibrations have to be considered in addition to the light-matter coupling. In general, the PL properties are also extremely sensitive to internal electric fields and to the dielectric environment (such as in photonic crystals) which impose further degrees of complexity. A precise microscopic description is provided by the semiconductor luminescence equations.

Ideal quantum-well structures

An ideal, defect-free semiconductor quantum well structure is a useful model system to illustrate the fundamental processes in typical PL experiments. The discussion is based on results published in Klingshirn (2012) and Balkan (1998).

The fictive model structure for this discussion has two confined quantized electronic and two hole subbands, e1, e2 and h1, h2, respectively. The linear absorption spectrum of such a structure shows the exciton resonances of the first (e1h1) and the second quantum well subbands (e2, h2), as well as the absorption from the corresponding continuum states and from the barrier.

Photoexcitation

In general, three different excitation conditions are distinguished: resonant, quasi-resonant, and non-resonant. For the resonant excitation, the central energy of the laser corresponds to the lowest exciton resonance of the quantum well. No, or only a negligible amount of the excess, energy is injected to the carrier system. For these conditions, coherent processes contribute significantly to the spontaneous emission. The decay of polarization creates excitons directly. The detection of PL is challenging for resonant excitation as it is difficult to discriminate contributions from the excitation, i.e., stray-light and diffuse scattering from surface roughness. Thus, speckle and resonant Rayleigh-scattering are always superimposed to the incoherent emission.

In case of the non-resonant excitation, the structure is excited with some excess energy. This is the typical situation used in most PL experiments as the excitation energy can be discriminated using a spectrometer or an optical filter. One has to distinguish between quasi-resonant excitation and barrier excitation.

For quasi-resonant conditions, the energy of the excitation is tuned above the ground state but still below the barrier absorption edge, for example, into the continuum of the first subband. The polarization decay for these conditions is much faster than for resonant excitation and coherent contributions to the quantum well emission are negligible. The initial temperature of the carrier system is significantly higher than the lattice temperature due to the surplus energy of the injected carriers. Finally, only the electron-hole plasma is initially created. It is then followed by the formation of excitons.

In case of barrier excitation, the initial carrier distribution in the quantum well strongly depends on the carrier scattering between barrier and the well.

Relaxation

Initially, the laser light induces coherent polarization in the sample, i.e., the transitions between electron and hole states oscillate with the laser frequency and a fixed phase. The polarization dephases typically on a sub-100 fs time-scale in case of nonresonant excitation due to ultra-fast Coulomb- and phonon-scattering.

The dephasing of the polarization leads to creation of populations of electrons and holes in the conduction and the valence bands, respectively. The lifetime of the carrier populations is rather long, limited by radiative and non-radiative recombination such as Auger recombination. During this lifetime a fraction of electrons and holes may form excitons, this topic is still controversially discussed in the literature. The formation rate depends on the experimental conditions such as lattice temperature, excitation density, as well as on the general material parameters, e.g., the strength of the Coulomb-interaction or the exciton binding energy.

The characteristic time-scales are in the range of hundreds of picoseconds in GaAs; they appear to be much shorter in wide-gap semiconductors.

Directly after the excitation with short (femtosecond) pulses and the quasi-instantaneous decay of the polarization, the carrier distribution is mainly determined by the spectral width of the excitation, e.g., a laser pulse. The distribution is thus highly non-thermal and resembles a Gaussian distribution, centered at a finite momentum. In the first hundreds of femtoseconds, the carriers are scattered by phonons, or at elevated carrier densities via Coulomb-interaction. The carrier system successively relaxes to the Fermi–Dirac distribution typically within the first picosecond. Finally, the carrier system cools down under the emission of phonons. This can take up to several nanoseconds, depending on the material system, the lattice temperature, and the excitation conditions such as the surplus energy.

Initially, the carrier temperature decreases fast via emission of optical phonons. This is quite efficient due to the comparatively large energy associated with optical phonons, (36meV or 420K in GaAs) and their rather flat dispersion, allowing for a wide range of scattering processes under conservation of energy and momentum. Once the carrier temperature decreases below the value corresponding to the optical phonon energy, acoustic phonons dominate the relaxation. Here, cooling is less efficient due their dispersion and small energies and the temperature decreases much slower beyond the first tens of picoseconds. At elevated excitation densities, the carrier cooling is further inhibited by the so-called hot-phonon effect. The relaxation of a large number of hot carriers leads to a high generation rate of optical phonons which exceeds the decay rate into acoustic phonons. This creates a non-equilibrium "over-population" of optical phonons and thus causes their increased reabsorption by the charge-carriers significantly suppressing any cooling. Thus, a system cools slower, the higher the carrier density is.

Radiative recombination

The emission directly after the excitation is spectrally very broad, yet still centered in the vicinity of the strongest exciton resonance. As the carrier distribution relaxes and cools, the width of the PL peak decreases and the emission energy shifts to match the ground state of the exciton (such as an electron) for ideal samples without disorder. The PL spectrum approaches its quasi-steady-state shape defined by the distribution of electrons and holes. Increasing the excitation density will change the emission spectra. They are dominated by the excitonic ground state for low densities. Additional peaks from higher subband transitions appear as the carrier density or lattice temperature are increased as these states get more and more populated. Also, the width of the main PL peak increases significantly with rising excitation due to excitation-induced dephasing and the emission peak experiences a small shift in energy due to the Coulomb-renormalization and phase-filling.

In general, both exciton populations and plasma, uncorrelated electrons and holes, can act as sources for photoluminescence as described in the semiconductor-luminescence equations. Both yield very similar spectral features which are difficult to distinguish; their emission dynamics, however, vary significantly. The decay of excitons yields a single-exponential decay function since the probability of their radiative recombination does not depend on the carrier density. The probability of spontaneous emission for uncorrelated electrons and holes, is approximately proportional to the product of electron and hole populations eventually leading to a non-single-exponential decay described by a hyperbolic function.

Effects of disorder

Real material systems always incorporate disorder. Examples are structural defects in the lattice or disorder due to variations of the chemical composition. Their treatment is extremely challenging for microscopic theories due to the lack of detailed knowledge about perturbations of the ideal structure. Thus, the influence of the extrinsic effects on the PL is usually addressed phenomenologically. In experiments, disorder can lead to localization of carriers and hence drastically increase the photoluminescence life times as localized carriers cannot as easily find nonradiative recombination centers as can free ones.

Researchers from the King Abdullah University of Science and Technology (KAUST) have studied the photoinduced entropy (i.e. thermodynamic disorder) of InGaN/GaN p-i-n double-heterostructure and AlGaN nanowires using temperature-dependent photoluminescence. They defined the photoinduced entropy as a thermodynamic quantity that represents the unavailability of a system's energy for conversion into useful work due to carrier recombination and photon emission. They have also related the change in entropy generation to the change in photocarrier dynamics in the nanowire active regions using results from time-resolved photoluminescence study. They hypothesized that the amount of generated disorder in the InGaN layers eventually increases as the temperature approaches room temperature because of the thermal activation of surface states, while an insignificant increase was observed in AlGaN nanowires, indicating lower degrees of disorder-induced uncertainty in the wider bandgap semiconductor. To study the photoinduced entropy, the scientists have developed a mathematical model that considers the net energy exchange resulting from photoexcitation and photoluminescence.

Photoluminescent materials for temperature detection

In phosphor thermometry, the temperature dependence of the photoluminescence process is exploited to measure temperature.

Experimental methods

Photoluminescence spectroscopy is a widely used technique for characterisation of the optical and electronic properties of semiconductors and molecules. The technique itself is fast, contactless, and nondestructive. Therefore, it can be used to study the optoelectronic properties of materials of various sizes (from microns to centimeters) during the fabrication process without complex sample preparation. For example, photoluminescence measurements of solar cell absorbers can predict the maximum voltage the material could produce. In chemistry, the method is more often referred to as fluorescence spectroscopy, but the instrumentation is the same. The relaxation processes can be studied using time-resolved fluorescence spectroscopy to find the decay lifetime of the photoluminescence. These techniques can be combined with microscopy, to map the intensity (confocal microscopy) or the lifetime (fluorescence-lifetime imaging microscopy) of the photoluminescence across a sample (e.g. a semiconducting wafer, or a biological sample that has been marked with fluorescent molecules). Modulated photoluminescence is a specific method for measuring the complex frequency response of the photoluminescence signal to a sinusoidal excitation, allowing for the direct extraction of minority carrier lifetime without the need for intensity calibrations. It has been used to study the influence of interface defects on the recombination of excess carriers in crystalline silicon wafers with different passivation schemes.

Inequality (mathematics)

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Inequality...