The heat treatment effect on the spectral and luminescent properties of sodium-germanate glass with CdS

The nucleation of CdS quantum dots in a sodium germanate glass matrix by means of isothermal treatment is demonstrated. It is shown that a sufficiently high concentration of cadmium ions in the initial glass results in nucleation of fairly big quantum dots. The luminescence of CdS is mainly of a trap nature and is localized in the region of 600−900 nm. Excess cadmium ions and nucleation of quantum dots in oxide glass lead to the defect nature of the luminescence bands: mainly associated with interstitial cadmium ions (ICd), the donor-acceptor pairs [V_Cd-V_S], and deep trap levels created by volume cadmium vacancies. The luminescence quantum yield of CdS quantum dots is less than 1%, indicating that nonradiative recombination of charge carriers is the dominant process.