Temperature dependent photoluminescence of nanocrystalline γ-CuCl hybrid films

Abstract

Organic–inorganic hybrid films combine the basic properties of organic and inorganic materials and offer special advantages that enhance optical, thermal and mechanical properties. We have studied the temperature dependent photoluminescence (PL) of nanocrystalline γ-CuCl hybrid films from 15K to room temperature in order to investigate the electronic transitions of the hybrid films. The I1 impurity bound exciton peak is the most intense emission peak at 15K but the peak intensity decreases rapidly with increasing temperature due to the low binding energy of this exciton bound to an impurity center and above 80K all three excitonic and biexcitonic peaks, except the Z3 free exciton emission peak disappeared. The biexciton emission peak intensity follows a quadratic dependency on power in the excitation power range <10 kWcm−2. The integrated Z3 excitonic PL intensity is almost independent of the temperature below 80K, while above 100K the PL emission intensity decreases rapidly. Thermal quenching of the Z3 free exciton PL emission in hybrid films has been observed. The full width at half maximum (FWHM) of the free exciton peak was investigated as a function of temperature and was explained by a theoretical model which considers the scattering of excitons with acoustic phonons and longitudinal optical phonons. The FWHM of the Z3 free exciton emission peak increases with increasing temperature, and a value of ~76meV was deduced for the FWHM at room temperature, which is comparatively better than ZnO (106meV) and GaN (100meV) nanostructures. The Z3 free exciton energy of the hybrid films exhibits a blue shift of 3meV at 15K compared to the bulk CuCl samples which may be due to a dead layer effect near the CuCl nanocrystal surface. The exciton energy also presents a blue shift of ~41meV with increasing temperature from 15K to room temperature. The results obtained for the γ-CuCl hybrid films are comparable to those of vacuum evaporated and sputtered CuCl films reported in the literature.