Optical spectra of free and supported CuCl microcrystals produced by thermal evaporation in a helium gas stream

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Abstract
Time-resolved measurements of the extinction spectra of free CuCl microcrystals and of CuCl microcrystals collected on a glass substrate have been performed at various growth stages after the beginning of evaporation in a low-pressure helium gas. Absorption bands due to Z1,2 and Z3 excitons were observed, which were shifted in energy from their bulk positions owing to exciton confinement effects. Initially the energy difference between the Z1,2 and the Z3 bands is considerably larger than its bulk value, and with increasing time it decreases and approaches the bulk value. The observed Z3 exciton absorption bands are compared with those calculated using an extended Mie theory, in which non-local effects as well as the size quantization of the excitonic states are included.