Temperature and excitation dependence of stimulated emission and spontaneous emission in InGaN epilayer

Temperature and excitation dependent photoluminescence(PL) of InGaN epilayer grown on c-plane Ga N/sapphire template by molecular beam epitaxy(MBE) has been systematically investigated. The emission spectra of the sample consisted of strong multiple peaks associated with one stimulated emission(SE) located at 430 nm and two spontaneous emissions(SPE) centered at about 450 nm and 480 nm, indicating the co-existence of shallow and deep localized states.The peak energy of SE exhibiting weak s-shaped variation with increasing temperature revealed the localization effect of excitons. Moreover, an abnormal increase of the SPE intensity with increasing temperature was also observed, which indicated that the carrier transfer between the shallow and deeper localized states exists. Temperature dependent time-resolved PL(TRPL) demonstrated the carrier transfer processes among the localized states. In addition, a slow thermalization of hot carriers was observed in InGaN film by using TRPL and transient differential reflectivity, which is attributed to the phonon bottleneck effect induced by indium aggregation.

Room temperature preparation of highly stable cesium lead halide perovskite nanocrystals by ligand modification for white lightemitting diodes

The poor stability of halide perovskite nanocrystals(NCs)has severely hindered future practical application.Herein,we proposed a facile and effective ligand modification route to synthesize stable CsPbBr_(3) nanocrystals by introducing a double-terminal ligand,namely 4,4'-Azobis(4-cyanovalericacid)(CA),to replace the conventional oleic acid(OA)ligand at room temperature.The as-synthesized CsPbBr_(3)-CA not only possesses high photoluminescence quantum yield(72%)related to the reduced trap defects,but also shows significantly improved stability exposure to water,ethanol,light,and/or heat benefiting from the CA ligand anchored to NC surfaces tightly.The photoluminescence intensity of CsPbBr_(3)-CA maintains about 80%and 75%of its initial emission intensity after immersed in water or ethanol for 360 min,respectively,whereas that of the CsPbBr_(3)-OA was quenched completely within a few minutes.Moreover,an all-inorganic white light-emitting diode(LED)covered 126%National Television System Committee(NTSC)standard and 92%Rec.2020 standard was fabricated by combining the green CsPbBr_(3)-CA and commercial red-emitting K2SiF6:Mn4+(KSF)phosphors onto a blue LED chip.Thus,the presented work initiates the development of the room temperature preparation of high quality CsPbBr_(3) and shows prospect for next-generation displays.

Stimulated emission at 1.54 μm from erbium/oxygen-doped silicon-based light-emitting diodes

Silicon-based light sources, including light-emitting diodes(LEDs) and laser diodes(LDs) for information transmission, are urgently needed for developing monolithic integrated silicon photonics. Silicon with erbium ions(Er^(3+)) doped by ion implantation is considered a promising approach, but it suffers from an extremely low quantum efficiency. Here we report an electrically pumped superlinear emission at 1.54 μm from Er/O-doped silicon planar LEDs, which are produced by applying a new deep cooling process. Stimulated emission at room temperature is realized with a low threshold current of ~6 mA(~0.8 A∕cm^(2)). Time-resolved photoluminescence and photocurrent results have revealed the complex carrier transfer dynamics by relaxing electrons from the Si conduction band to the Er^(3+) ion. This picture differs from the frequently assumed energy transfer via electron–hole pair recombination of the silicon host. Moreover, the amplified emission from the LEDs is likely due to a quasi-continuous Er/O-related donor band created by the deep cooling technique. This work paves the way for fabricating superluminescent diodes or efficient LEDs at communication wavelengths based on rare-earth-doped silicon.