Spectroscopic and energy-transfer parameters for Er3+-doped and Er3+, Pr3+-codoped GeGaS glasses

The absorption and emission spectra and the rate parameters for the important energy-exchange processes relevant to the ⁴I _11/2 → ⁴I_13/2 laser transition in Er ³⁺-doped and Er³⁺, Pr³⁺-codoped GeGaS glasses are presented. The rate parameters are determined after optical excitation with a tunable pulsed optical parametric oscillator that excites the ⁴I_11/2 and ⁴I_13/2 energy levels directly. For the Er³⁺ singly doped samples, the energy-transfer upconversion (ETU) macroscopic rate parameters for the upper and lower laser levels were measured for a range of Er^3- concentrations. In correspondence with ZBLAN and the fluoride crystals, the (⁴I _13/2, ⁴I_13/2) → (⁴I _9/2, ⁴I_15/2) ETU process of the lower laser level is measured to be stronger than the corresponding ETU process of the upper laser level. Such a condition enables energy recycling to occur. A higher rate of energy transfer from the ⁴I_13/2 level of Er ³⁺ to Pr³⁺ deactivator is measured as compared with the corresponding energy transfer from ⁴I_11/2 level to both the Pr³⁺ deactivator and OH impurity. With these favorable energy-transfer conditions, the prospect for the future development of highly efficient ∼3-μm fiber lasers with GeGaS glass as the host material is excellent.