Infrared emission and ion-ion interactions in thulium- and terbium-doped gallium lanthanum sulfide glass

Infrared emission at 0.7, 0.8, 1.2, 1.5, 1.8, 2.3, 3.8, and 4.8 mu m is measured in thulium- (Tm3+) and terbium(Tb3+) doped gallium lanthanum sulfide (GLS) glass. Emission cross sections are calculated from the absorption and emission spectra by use of Judd-Ofelt analysis, the Fuchtbauer-Ladenburg equation, and the theory of McCumber. Fluorescence and lifetime measurements confirm energy transfer from Tm3+ to Tb3+ ions and reveal a number of new cross-relaxation and upconversion processes between Tm3+ ions involving the F-3(2,3) and H-3(5) levels that can be observed only in low-phonon-energy materials. These processes indicate that the most efficient pump wavelength for the 1.2- and 3.8-mu m transitions is 0.7 mu m. The Tm3+ fluorescence at 3.8 mu m coincides with an atmospheric transmission window, and the Tb3+ fluorescence at 4.8 mu m overlaps the fundamental absorption of carbon monoxide, making the glass a potential fiber laser source for remote-sensing and gas-sensing applications. (C) 1999 Optical Society of America [S0740-3224(99)01902-5].