The time evolution of nanoscale structure formation on the surface of CdI2 crystals grown both from the melt and from the gas phase is investigated. Atomic force microscopy was used to show that, already at the initial stages of exposure to air at room temperature, island-shaped nanostructures form, which subsequently aggregate into nanoclusters as the exposure time increases. Similar nanostructures, including nanopores and nanoclusters, are observed for CdI2 crystals grown from the gas phase after prolonged exposure to air. Photoluminescence spectroscopy indicates that the formed nanoclusters are consistent with the presence of cadmium hydroxide (Cd(OH)2) and cadmium oxide (CdO). The formation of nanostructures determines the time evolution of the low-temperature luminescence spectra of CdI2 crystals. Additional bands with maxima at 1.87 eV and long-wavelength luminescence in the region with a maximum at 1.68 eV appear in the spectral structure. These results highlight the close relationship between surface structural evolution and the time-dependent optical properties of CdI2.
Rovetskii et al. (Sun,) studied this question.