Effect of Tb3+ co-doping on the electron population densities of Tm3+ in Ge–As–Ga–S glasses

Abstract

The 1.48-μm emission properties and electron population densities of the excited levels were investigated for Ge–As–Ga–S glasses doped with Tm3+ or Tm3+/Tb3+. Electron population inversion between the H43 and F43 levels in Tm3+ cannot be achieved without Tb3+ addition due to the strong cross-relaxation in Tm3+. Co-doping of Tb3+ resulted in the large decrease in the population density of the Tm3+:F43 level via the energy transfer of Tm3+:3F4→Tb3+:7F0,1,2. Calculated population densities of the two levels in Tm3+ using the rate equations showed that the population inversion became possible through the addition of Tb3+.