OXIDATION OF CADMIUM CHALCOGENIDE MICROCRYSTALS DOPED IN SILICA GLASSES PREPARED BY THE SOL-GEL PROCESS

Crystallites of CdS, CdSe, or CdTe were doped in glasses prepared by t he sol-gel process. The oxidation of the crystals during heating at 30 0-400-degrees-C in air was studied using optical absorption, X-ray dif fraction and X-ray photo-electron experiments. Cadmium chalcogenides d oped in SiO2 glasses reacted with oxygen, forming CdO and SO2, SeO2, o r TeO2 when heated at temperatures above 300-degrees-C in air. The met al oxides remained in the samples in an amorphous state. SO2 evaporate d. The optical absorption coefficients for cadmium chalcogenides decre ased exponentially with the time of heat treatment. The rate constant of oxidation decreased in the order CdTe much greater than CdS > CdSe. The activation energy for the oxidation of these materials was estima ted to be 111+/-6 kJ/mol. The samples in which crystals were oxidized again precipitated cadmium chalcogenide crystals when heated again in H-2 at temperatures > 300-degrees-C or reacted with H2S gas above room temperature.