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We report on ultrafast carrier dynamics in nanocrystalline CdSe thin films prepared by chemical solution deposition. The photoluminescence and transient absorption dynamics have spectrally dependent decay faster at shorter wavelengths. The spectral behavior of the decay rates in samples with different nanocrystal sizes and the sensitivity of the dynamics on the surface modification indicate the dominant role of the surface states in the photoluminescence.

The dynamics of absorption bleaching in CdS nanocrystalline thin films were studied in the temperature interval 10-300 K and three distinct decay time constants (sub-ps, ps, and ns) were identified. We interpreted the dynamics in terms of three groups of nanocrystals with specific defects and showed that two of them are related. A close link between the temperature behaviour of the photoluminescence efficiency and that of the relative amplitude of the nanosecond component was observed and an explanation based on a microscopical model was proposed. The optical nonlinearities were studied by self-diffraction technique. A dephasing time constant shorter than 80 fs and a value of jc 3 j % 6 Â 10 --16 m 2 V --2 were obtained.