Decreased fast time scale spectral diffusion of a nonpolar InGaN quantum dot

Spectral diffusion can lead to considerable broadening of the line width of nitride quantum dots. Here, InGaN quantum dots grown on a nonpolar plane were shown to exhibit a decreased spectral diffusion rate compared to polar nitride dots. A robust intensity correlation method was used to measure the spectral diffusion rate of six quantum dots. A maximum spectral diffusion time of 1170 ± 50 ns was found. An increase of the rate with increasing power was observed. The decreased internal field leads to a lifetime for the nonpolar dots that is shorter than that for polar dots; the important ratio of spectral diffusion time to lifetime is more favorable for nonpolar quantum dots, thereby increasing the chances of generating indistinguishable photons

Enhanced photoluminescence quantum yield of MAPbBr(3) nanocrystals by passivation using graphene

Diminishing surface defect states in perovskite nanocrystals is a highly challenging subject for enhancing optoelectronic device performance. We synthesized organic/inorganic lead-halide perovskite MAPbBr(3) (MA = methylammonium) clusters comprising nanocrystals with diameters ranging between 20-30 nm and characterized an enhanced photoluminescence (PL) quantum yield (as much as ~ 7 times) by encapsulating the MAPbBr(3) with graphene (Gr). The optical properties of MAPbBr(3) and Gr/MAPbBr(3) were investigated by temperature-dependent micro-PL and time-resolved PL measurements. Density functional theory calculations show that the surface defect states in MAPbBr(3) are removed and the optical band gap is reduced by a 0.15 eV by encapsulation with graphene due to partial restoration of lattice distortions