Trap States in Cd(S,Se) Nanocrystals Probed by Photomodulation Spectroscopy

Intensity, temperature and frequency-dependent photoabsorption spectroscopy are used to probe trap states in CdS0.44Se0.56 nanoparticles in glass. The photoabsorption signal from 6.2 nm radius particles is found to be a combination of two effects: bleaching, due to phase space filling, and an electric-field effect. Frequency-dependent photoabsorption data show that the electric-field effect is caused by a long-lived (τ = 30 /μs at T=293 K) trap state and that the bleaching occurs on a faster time scale. The trap activation energy obtained from the temperature dependence of the lifetime is 0.23 ± 0.06 eV. Only bleaching is observed in the smaller nanocrystallites.