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

Abstract

Infrared emission at 0.7, 0.8, 1.2, 1.5, 1.8, 2.3, 3.8, and 4.8 µm is measured in thulium- $({\mathrm{Tm}}^{3+})$ and terbium- $({\mathrm{Tb}}^{3+})$ doped gallium lanthanum sulfide (GLS) glass. Emission cross sections are calculated from the absorption and emission spectra by use of Judd–Ofelt analysis, the Füchtbauer–Ladenburg equation, and the theory of McCumber. Fluorescence and lifetime measurements confirm energy transfer from ${\mathrm{Tm}}^{3+}$ to ${\mathrm{Tb}}^{3+}$ ions and reveal a number of new cross-relaxation and upconversion processes between ${\mathrm{Tm}}^{3+}$ ions involving the ${ }^3{\mathrm{F}}_{2,3}$ and ${ }^3{\mathrm{H}}_5$ 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-µm transitions is 0.7 µm. The ${\mathrm{Tm}}^{3+}$ fluorescence at 3.8 µm coincides with an atmospheric transmission window, and the ${\mathrm{Tb}}^{3+}$ fluorescence at 4.8 µm overlaps the fundamental absorption of carbon monoxide, making the glass a potential fiber laser source for remote-sensing and gas-sensing applications.