ABSTRACT
Ultraviolet light-emitting diodes based on Al-rich AlGaN semiconductors operating in the 210 nm-280 nm have drawn significant interest for many critical applications, including water purification, disinfection of air and surface as preventive measures of SARS COV-2, sterilization, etc. However, for the above-mentioned applications, the current technology still relies on toxic and inefficient mercury-based UV lamps. Driven by the immense need for an efficient, mercury-free, compact alternative technology, future water purification and disinfection technologies require the development of high-efficiency UV-C light-emitting diodes. To date, the external quantum efficiency (EQE) in AlGaN quantum well (QW) UV-LED heterostructures has been severely limited due to several factors including large densities of defects/dislocations, extremely low light extraction efficiency (LEE) of dominant transverse magnetic (TM) light, absorptive p -GaN contact, and total internal reflection (TIR). © 2022 IEEE.
ABSTRACT
The COVID-19 pandemic has generated great interest in ultraviolet (UV) disinfection, particularly for air disinfection. Although UV disinfection was discovered close to 90 years ago, only very recently has it reached the consumer market and achieved much acceptance from the public, starting in the 2000s. The current UV light source of choice has been almost exclusively a low-pressure mercury vapor discharge lamp. Today, however, with emerging deep-UV (DUV) chip-scale technologies, there has been a significant advancement, along with ever-increasing interest, in the development and deployment of disinfection systems that employ compact devices that emit in the deep-UV spectral band (200- 280 nm), including UV light-emitting diodes (LEDs) and cathodoluminescent (CL) chips. This perspective looks into competing UV technologies (including mercury lamps and excimer lamps as benchmarks) on their optical merits and demerits and discusses the emerging chip-scale technologies of DUV electroluminescent and cathodoluminescent devices, comparing them against the benchmarks and providing an overview of the challenges and prospects. The accelerating progress in chip-scale solutions for deep-UV light sources promises a bright future in UV disinfection.
ABSTRACT
Owing to the pandemic of Coronavirus disease 2019 (COVID-19), the demands on ultracold-chain logistics have rapidly increased for the storage and transport of mRNA vaccines. Herein, we report a soluble luminescent thermometer based on thermally activated dual-emissions of Mn2+-alloyed 2D perovskite quantum wells (QWs). Owing to the Mn2+ alloying, the binding energy of perovskite QW exciton is reduced from 291 to 100 meV. It facilitates the dissociation of excitons into free charge carriers, which are then transferred and trapped on Mn2+. The temperature-dependent charge transfer efficiency can be tuned from 8.8% (-93 °C) to 30.6% (25 °C), leading to continuous ratiometrical modulation from exciton-dominated violet emission to Mn2+-dominated orange emission. The highest sensitivity (1.44% per K) is approximately twice that of the Mn2+-doped chalcogenide quantum dots. Taking advantage of highly reversible color switching, Mn2+-alloyed QWs provide an economical solution to monitor the ultracold-chain logistics of the COVID-19 vaccine. © 2022 American Chemical Society.