Energy transfer processes in Yb3+–Tm3+ co-doped sodium alumino-phosphate glasses with improved1.8 µm emission

Abstract

Sodium alumino-phosphate glasses co-doped withYb3+ andTm3+ ions have been preparedwith notably low OH− content, and characterized from the viewpoint of their spectroscopic properties. In these glasses,Yb3+ acts as an efficient sensitizer of excitation energy at0.98 µm—which can be provided by high power and low cost diodelasers, and subsequently undergoes non-resonant energy transfer toTm3+ ions(2F5/2,, 3H5). Through this process,the emitting level 3F4 is rapidly populated, generating improved emission at1.8 µm (). In order to guarantee the efficiency of such favorable energy transfer, energy lossesvia multiphonon decay, Yb–Yb radiative trapping, and non-radiative transfer toOH− groups were evaluated, and minimized when possible. The dipole–dipole energy transfermicroscopic parameters corresponding to , and transfers, calculated by the Förster–Dexter model, areCYb−Tm = 2.9 × 10−40 cm6 s−1,CYb−Yb = 42 × 10−40 cm6 s−1 and CTm−Tm = 43 × 10−40 cm6 s−1, respectively.