Ultrafast recombination and photoluminescence spectra of semiconductor microcrystallites

The photoluminescence spectra of CdS_xSe_1-x doped glasses were found to be strongly dependent on the pumping laser intensity. Two spectral features corresponding to two different recombination mechanisms can be identified. The dynamic behavior can be qualitatively explained by the competition between (A) tunneling-mediated recombination of deeply trapped charges and (B) direct geminate recombination of excitons and nongeminate radiative recombination of free and shallowly trapped carriers and (C) nonradiative recombination. Large (> 30 nm) blueshifts of both peaks were also observed as the laser intensity increased. Additionally, it was found that both the fluorescence spectrum and the recombination lifetime of these microcrystallites could be modified by laser irradiation. Recombination times faster than 10 ps can be achieved in these materials.