Enhanced photo-response of thin-film structures with nanocrystals

Thin-film multilayers with dielectric and semiconductor nanolayers of 200-10 nm thicknesses have been deposited by thermal evaporation onto irradiation-resistive substrates using pure crystals as evaporated targets. Some multilayers were γ-irradiated in air at room temperature with dose of 83 kGy. X-ray diffraction and microscopy studies reveal that the multilayers consist of nanometer-sized crystals with cubic structure and defined size. Film structures were oriented along the (1 1 1) plane. Absorption spectra of non-irradiated LiF nanocrystals of 100 nm size and those of initial crystals give evidence of metal colloids presence. Photoluminescence spectra of γ-irradiated nanostructures with various LiF content show the enhancement of F3+-colour centres excitation in the region of metal colloids absorption and the increase is observed between emission intensities of F3+ and F2 centers with respect to initial crystals γ-coloured in identical conditions. Emission intensities of both centers under excitation in the M band correlate with LiF content. These effects, which are related to high-quality nanocrystals, but at the same time depend strongly on the defect content, especially as far as their 1-2 ps nonlinearities are concerned, could depend on nanocrystal purity and metal excess collection in their boundaries regions.