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Spectroscopic properties and energy transfer parameters of Tm3+ ions in gallium lanthanum sulfide glass

This work presents the spectroscopic characterization of Tm3+ doped gallium lanthanum sulfide (GaLaS) chalcogenide glass through absorption, fluorescence and lifetime measurements of excited3H4 and3F4 states, and a study of Tm3+:Tm3+ energy transfer. The cross relaxation 3 H 4,3 H 6 →3 F 4,3 F 4 responsible for the pumping of level3F4 and the laser transition at 1800 nm (3 F 4 →3 H 6), as well as the energy migration 3 H 4,3 H 6 →3 H 4,3 H 6 processes are studied in terms of the microscopic parameters of energy transfer Cda and Cdd obtained by the Kushida model of multipolar interactions and by a rate equation treatment of the dynamics of levels3F4 and3H4. From this treatment it was possible to simulate level3F4 temporal evolution curves for different Tm3+ concentrations, leading to results that are in excellent agreement with experimental ones. All the samples studied in the work present positive optical gain coefficients for excitation densities higher than 12 kW cm−2 indicating the potentiality of GaLaS:Tm3+ glass as a mid-infrared laser active medium.