Professor Robert Taylor

Abstract:

Diminishing surface defect states in perovskite nanocrystals is a highly challenging subject for enhancing optoelectronic device performance. We synthesized organic/inorganic lead-halide perovskite MAPbBr3 (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 MAPbBr3 with graphene (Gr). The optical properties of MAPbBr3 and Gr/MAPbBr3 were investigated by temperature-dependent micro-PL and time-resolved PL measurements. Density functional theory calculations show that the surface defect states in MAPbBr3 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.

Abstract:

Because of the strong strain in nitrides, superlattice layers have been used to release the strain in the QW and reduce the quantum confined Stark effect. However, few reports discuss comprehensively the strain relaxation behavior and optical performance of a GaN/AlGaN single quantum well (QW) with inserted GaN/AlGaN superlattices (SLs). In this work, we examined a group of graded Al content GaN/Al_xGa_1–xN SL layers under the GaN/Al_0.3Ga_0.7N single QW grown on c-plane sapphire. Both the excitation power and temperature dependence of the time-integrated micro-photoluminescence (μ-PL) and time-resolved μ-PL were measured. The samples exhibited very narrow UV emission and had almost unchanged emission wavelength and stable line width behavior with excitation power as well as “S-shape” and weak “W-shape” characteristics with temperature due to the localization. The temperature-dependent PL lifetime was measured from 5 to 300 K, and the relatively fast recombination lifetime of the two samples was examined. Micro-Raman spectroscopy was also conducted to probe the strain state. All the results showed that adopting SLs around the QW structure produced a much more stable and desirable performance, which can be attributed to an effective relaxation of the strain in the QW.

Abstract:

This is a micro-photoluminescence(micro-PL) based study to investigate the optical property of surface passivation effect with Pb(OH)2 coated CsPbBr3 micro/nano rods and demonstration of stimulated emission from defect states. We also presented a technique with completely separable excitation and collection in a confocal microscopy. In this work, we have supported with data from time-resolved study, time-integrated PL map and scan with either collection/excitation fixed and scanning the other.

Abstract:

The updated data files are supporting demonstration of weak coupling between a cavity mode and emission from a single quantum dot. In this research (done by January 2020) we developed an easily controlled fabrication process to deterministically write a mode gap cavity over a photonics crystal waveguide. All data files uploaded here are obtained through micro-photoluminescence(PL) experiments. Those associated with 'fig2' are the single time-integrated PL spectra with the first column in the data file being wavelength in 'nm'. fig2 a and b are single PL spectra of high and low density of ensemble quantum dots emission before coating the cavity. fig2 c is showing the crossover between the cavity emission mode and the quantum dot spectrum over a temperature run. fig 3 data is the time-resolved PL data taken at temperatures of 6K and 30K demonstrating Purcell enhancement. The corresponding instrument response function (irf) of the excitation laser signal is also included for deconvolution. NB: This is Version 2 of the data and supercedes Version 1 at https://doi.org/10.5287/bodleian:dXbD81ZmD