Relaxation dynamics in photoexcited GaSe nanoparticles

The photophysics and relaxation dynamics of GaSe nanoparticles have been studied in room temperature solutions, using static and time-resolved emission spectroscopy. Following 400 nm excitation, these particles exhibit a static emission maximum at 480 nm. This emission is polarized and the anisotropy is largest on the blue edge of the emission spectrum. Both the total (unpolarized) emission kinetics and the emission anisotropy kinetics are obtained. Static emission spectra along with wavelength-dependent kinetic results permit the reconstruction of time-dependent spectra. The kinetic results reported here show an 80 ps decay component in the total emission, but not in the anisotropy decay kinetics. There is an similar to270 cm(-1) shift in the emission maximum during this decay. This transient is assigned to direct to indirect band edge relaxation. This is followed by a 400 ps decay in both the total emission and the anisotropy kinetics. A very small shift (similar to170 cm(-1)) in the emission maximum occurs during this decay. This transient is assigned to trapping of holes in shallow acceptor levels. Finally, there is a 2.4 ns decay of both the total emission and the emission anisotropy. As this decay occurs, the 480 nm emission is replaced by a much weaker, broad and unpolarized 520 nm emission. This decay is assigned to relaxation of holes into deep traps. The kinetic results are interpreted in terms of a model which is based on the relative energetics of the direct and indirect band edges and the hole trap states in bulk GaSe. (C) 2002 American Institute of Physics.