Energy transfer processes in Yb3+–Tm3+co-doped sodium alumino-phosphate glasses with improved 1.8 µm emission

Sodium alumino-phosphate glasses co-doped with Yb 3+ and Tm 3+ ions have been prepared with notably low OH − content, and characterized from the viewpoint of their spectroscopic properties. In these glasses, Yb 3+ acts as an efficient sensitizer of excitation energy at 0.98 µm—which can be provided by high power and low cost diode lasers, and subsequently undergoes non-resonant energy transfer to Tm 3+ ions ( 2 F 5/2 , , 3 H 5 ). Through this process, the emitting level 3 F 4 is rapidly populated, generating improved emission at 1.8 µm ( ). In order to guarantee the efficiency of such favorable energy transfer, energy losses via multiphonon decay, Yb–Yb radiative trapping, and non-radiative transfer to OH − groups were evaluated, and minimized when possible. The dipole–dipole energy transfer microscopic parameters corresponding to , and transfers, calculated by the Förster–Dexter model, are C Yb−Tm = 2.9 × 10 −40 cm 6 s −1 , C Yb−Yb = 42 × 10 −40 cm 6 s −1 and C Tm−Tm = 43 × 10 −40 cm 6 s −1 , respectively.