Synthesis and properties of nanocrystalline CsI

The structure and properties of fine CsI powders prepared by spray pyrolysis and synthetic opal (SiO2) based composites containing CsI in their pores have been studied by electron microscopy, X-ray diffraction, and luminescence spectrometry. The powders consisted of nanocrystalline particles which increased in size from 35 to 55 nm with increasing pyrolysis temperature. In the opal/CsI composites, the CsI nanocrystallites were about 45–50 nm in size and formed a single three-dimensional network between the SiO2 spheres. In going from bulk crystals to their nanocrystalline analogs, the size effect on CsI luminescence leads to a reduction in luminescence yield, a redshift of the emission bands of the on-center and off-center self-trapped excitons (STEs), and an increase in the contribution of the off-center STEs to the net intrinsic emission yield. The emission decay kinetics of the off-center STEs is insensitive to the crystallite size.