Excitonic States and Related Optical Susceptibility in InN/AlN Quantum Well Under the Effects of the Well Size and Impurity Position

Based on the finite difference method, linear optical susceptibility, photoluminescence peak and binding energies of three first states of an exciton trapped by a positive charge donor-impurity ( ) confined in InN/AlN quantum well are investigated in terms of well size and impurity position. The electron, heavy hole free and bound excitons allowed eigen-values and corresponding eigen-functions are obtained numerically by solving one-dimensional time-independent Schrödinger equation. Within the parabolic band and effective mass approximations, the calculations are made considering the coupling of the electron in the n-th conduction subband and the heavy hole in the m-th valence subband under the impacts of the well size and impurity position. The obtained results show clearly that the energy, binding energy and photoluminescence peak energy show a decreasing behavior according to well size for both free and bound cases. Moreover, the optical susceptibility associated to exciton transition is strongly red-shift (blue-shifted) with enhancing the well size (impurity position).

Ligand Assisted Control of Photoluminescence in Organometal Perovskite Nanocrystals

Organometal perovskite nanocrystals have shown remarkable properties not only in photovoltaics, but also in light-emitting devices. In this work colloidal nanocrystals of organometal perovskite CH3NH3PbBr3 (MAPBr) with effective visible photoluminescence were synthesized by the ligand assisted reprecipitation method. The studies were carried out by photoluminescence spectroscopy and optical transmission spectroscopy. Analysis of the photoluminescence and transmission spectra showed that by changing the concentration of the ligands oleylamine and octylamine, it is possible to control the size of nanocrystals and the photoluminescence wavelength due to the quantum confinement effect. It was shown that the increase in ligands concentration in MAPBr perovskite nanocrystals (NCs) solutions decreases the width of the peak which indicates a better quality of the obtained nanocrystals. An increase in the band gap indicates a decrease in the size of the nanocrystals. Replacing the ligands in the colloidal perovskite NCs solutions leads to shift of the photoluminescence peak from 456 to 535 nm.

Using design of experiment to obtain a systematic understanding of the effect of synthesis parameters on the properties of perovskite nanocrystals

Design of experiments was used to systematically investigate the synthesis of MAPbI3 nanoparticles in a flow reactor. By controlling the solvents and the ligands, we were able to tune the MAPbI3 photoluminescence peak between 614 and 737 nm.

The Study on Tuning Photoluminescence of Colloidal Graphene Quantum Dots Synthesized through Laser Ablation

We report photoluminescence study of Colloidal Graphene Quantum Dots (GQDs) that synthesized from ablation of rGO solution. The rGO solution was ablated using 800 nm Ti-Sapphire femtosecond laser by varying the synthesize parameters such as laser power and ablation time. We observed that changing laser power 1 Watt to become 1.7 Watt and time ablation 20 minutes to become 60 minuteswill alterate the Photoluminescence (PL) curve peak of GQDs. In case of ablation power variation, PL data shows that the PL curve peak excited by 280 nm laser changed from 369.09 nm to 371.02 nm, and when it excited by 290 nm the PL curve peak slightly changed from 388.17 nm to 393.8 nm. The alteration of Photoluminescence peak is also observed in the variation of time ablation experiment, The PL curve peaks from GQDs time ablation variation samples excited by 280 nm were slightly changed from 376.81 nm to 373.59 nm, and when it excited by 290 nm laser, the PL curve peak is 391.55 nm then changed to 392.11. The change of PL peak on laser power or time ablation variation shows that both parameters will alter either the size, shape, or the edge-type of GQDs.