Resonant-Raman-scattering and photoluminescence studies in glass-composite and colloidal CdS

Abstract

Pressure-tuned resonant Raman scattering was used to determine the band-gap shift due to quantum size effects of microcrystalline CdS in glass composites and colloids. The wurtzite- to rocksalt-phase-transition behavior in the microcrystallite CdS systems was also studied and is quite different from that in bulk CdS. This different behavior is attributed to the large number of defects in microcrystallite CdS systems. We systematically investigated these defect properties in terms of the pressure coefficients of the photoluminescence peaks. This work demonstrates that the main defects in the CdS-glass composites are cadmium vacancies, ${\mathit{V}}_{\mathrm{Cd}}$; whereas in the CdS colloids the defects consist of cadmium vacancies, ${\mathit{V}}_{\mathrm{Cd}}$; sulfur vacancies, ${\mathit{V}}_{\mathrm{S}}$; interstitial sulfur, ${\mathit{I}}_{\mathrm{S}}$; and cadmium atoms adsorbed on the surface, ${\mathit{S}}_{\mathrm{Cd}}$.