Application of electroabsorption techniques to the study of crystal particles in glasses.
Glasses containing a small amount of CdS have an optical absorption edge which depends upon the heat treatment accorded the glass. The edge position agrees roughly with that of CdS crystals. Data for two glasses with absorption edges at about 2.45 eV and 2.52 eV are presented. The optical absorption spectra of such glasses have been modulated by application of ac electric fields. The spectral dependence of the modulated component of the absorption coefficient is strikingly different for glasses with different heat treatments. This difference is interpreted in terms of excitons and the crystal particle sizes and gives a consistent explanation of the shift in the absorption edge. Since the absorption edge in CdS crystals is due to excitons, it is suggested that the lower energy absorption edge results from crystal particle sizes large enough to permit exciton formation, whereas the higher energy edge results from smaller particle sizes that do not permit exciton formation. The electroabsorption spectrum for the glass with the lower energy edge qualitatively resembles the spectrum for CdS films, whose salient features are attributed to excitons.
Rockstad
H K
HK