Radiative and nonradiative lifetimes of band edge states and deep trap states of CdS nanoparticles determined by time-correlated single photon counting

Emission lifetimes of band edge and deep trap states of CdS nanoparticles w ith different surface capping were measured. For unpassivated nanoparticles with low fluorescence, the emission is dominated by deep trap states and t he decay (5 ns) is independent of excitation intensity. For surface passiva ted nanoparticles with strong luminescence, the emission is dominated by ba nd edge states with a fast and slow decay (a few ns and 50 ns). The slow de cay is independent of intensity and the fast component is strongly dependen t on intensity. The results support the model of exciton-exciton annihilati on upon trap state saturation at high intensities. (C) 2000 Elsevier Scienc e B.V. All rights reserved.