Photoluminescence and states in the bandgap of germanium sulfide glasses

We report the characteristic photoluminescence (PL) behavior in Ge1−xSx (0.60 ≦ x ≦ 0.90) chalogenide glasses. The compositional and excitation energy dependence of the PL spectra has been investigated. The PL spectra observed near 2.0 eV are strongly suggested to be the result of the recombination process between the photo-excited electrons at the bottom of the conduction band and holes in the defect levels based on their compositional dependence. We also found that the PL intensity is directly related to the concentration of neutral defects. Reduction of the PL through prolonged irradiation by excitation light has also been investigated and is found to recover after relaxation in the dark at room temperature. The states in the bandgap of the Ge–S chalcogenide glasses and their changes due to photo-irradiation are discussed.