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

The 1.48-mu m 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 H-3(4) and F-3(4) 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+:F-3(4) level via the energy transfer of Tm3+:F-3(4)-->Tb3+:F-7(0,1,2). 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+. (C) 2000 American Institute of Physics. [S0021-8979(00)05817-5].