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

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 Z 1,2 and Z 3 excitons were observed, which were shifted in energy from their bulk positions owing to exciton confinement effects. Initially the energy difference between the Z 1,2 and the Z 3 bands is considerably larger than its bulk value, and with increasing time it decreases and approaches the bulk value. The observed Z 3 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.