Optical properties of Ga–Ge–Sb–Se chalcogenide glasses doped with terbium and dysprosium ions, near the fundamental absorption band edge

In the paper, results of measurements of the optical response of chalcogenide glasses of the Ga$_5$Ge$_{20}$Sb$_{10}$Se$_{65}$ composition doped with rare-earth ions Tb$^{3+}$ or Dy$^{3+}$, in the wavelength range of 0.7–1.5 $\mu$m by the method of IR spectroscopy are presented. Parameters characterizing the fundamental absorption band edge of the glasses – optical bandgap energy, Urbach tail parameter and weak absorption tail parameter – have been evaluated. It has been found that doping in low concentrations (up to 0.3 wt%) does not influence the optical bandgap energy and optical properties of the glasses in the range of the Urbach tail, but in the range of the weak absorption tail, optical response of the glasses depends on the activator concentration. Crystallization of the glasses produced by the direct melting method also depends on the activator concentration. In the glasses doped with Dy$^{3+}$, absorption bands of the ion are located in the range of the weak absorption tail of the glass that makes possible energy transfer between the ions and the gap states of the charge carriers.