CsPbBr 3 and Cs 4 PbBr 6 perovskite powders have been synthesized through a relatively simple low-temperature and low-cost method. Nanocrystalline films have also been deposited from solutions with four different molar compositions of binary salt precursors. Optical absorption, emission and excitation spectra have been performed in the UV-visible spectral range while X-ray diffraction (XRD) has been recorded to characterize the nanocrystal morphology for the different molar compositions. A preferential orientation of crystallites along the (024) crystalline plane has been observed as a function of the different deposition conditions in films growth. All the crystals show an absorption edge around 530 nm; Tauc plots of the absorption returned bandgaps ranging from 2.29 to 2.35 eV characteristic of CsPbBr 3 phase. We attribute the UV absorption band peaked at 324 nm to the fundamental band-to-band transition for Cs 4 PbBr 6. It was observed that the samples with the most ordered Cs 4 PbBr 6 crystals exhibited the most intense emission of light, with a bright green emission at 520 nm, which are however due to the luminescence of the inclusion of CsPbBr 3 nanoclusters into the Cs 4 PbBr 6. The latter shows instead an intense UV emission. Differently, the pure CsPbBr 3 powder did not show any intense fluorescent emission. The excitation spectra of the green fluorescent emission in all samples closely resemble the CsPbBr 3 absorption with the peculiar dip around 324 nm as expected from density of state calculations reported in the literature.
Multidisciplinary Digital Publishing Institute
1 Jun 2019
Volume: 9 Issue: 6 Pages: 280