Annealing Behavior of Heavily Pb2+ -Doped CsCl Films studied by in situ Absorption Spectroscopy

We have applied absorption spectroscopy to the study of annealing behavior of heavily pb2+ -doped CsCl films prepared by coevaporation of the mixture of CsCl and PbCl2 onto low temperature (77K) silica-glass substrates. The as-prepared films exhibit localized optical absorption due to Pb2+ ions for the full range of PbCl2 concentration suggesting that the Pb2+ ions are embedded in the amorphous surroundings. When the films are annealed at 500K, the amorphous surroundings are crystallized, with the Pb2+ ions still localized forming impurity centers. On annealing the films of higher PbCl2 concentrations, the Pb2+ ions migrate to form CsPbCl3 (PbCl2 concentration, 30 to 60 mol%) or PbCl2 (60 to 100 mol%) crystals, both exhibiting a sharp exciton peal in their absorption spectrum. These results are also confirmed by the measurements of spectral change due to annealing of thin PbCl2 films quench deposited onto thick CsCl films