Generation of extremely photo-luminescent CuBr crystallites in the CuCl/KBr system (CuCl film on KBr crystal)

The behavior of thermally-induced generation of extremely photo-luminescent CuBr crystallites in the previously reported CuCl/KBr system has been investigated by in situ optical absorption and photoluminescence (PL) spectroscopy. Upon suitable annealing of the system, CuCl can be fully changed into CuBr characterized by extremely-high-intensity PL. The PL spectrum is generally composed of three emission bands due to free-exciton, bound-exciton and defect-related emissions, with their intensity ratio depending on the annealing history. For a suitably-annealed system, in which the bound-exciton emission is maximized and the defect-related one is minimized at 77 K, extremely-high-intensity free-exciton PL is observed at room temperature. The integrated intensity of the room temperature free-exciton PL is ∼103 times larger than that of CuCl, despite the general recognition that PL from CuBr is much weaker than that from CuCl.