Efficient Nd~(3+)→Yb~(3+) energy transfer processes in high phonon energy phosphate glasses for 1.0 μm Yb~(3+) laser

摘要

Efficient Nd~(3+)→Yb~(3+) resonant and phonon-assisted energy transfer processes have been observed in phosphate glasses and have been studied using steady-state and time-resolved optical spectroscopies. Results indicate that the energy transfer occurs via nonradiative electric dipole-dipole processes and is enhanced with the concentration of Yb~(3+) acceptor ions, having an efficiency higher than 75% for the glass doped with 1 mol% of Nd_2O_3 and 4 mol% of Yb_2O_3. The luminescence decay curves show a nonexponential character and the energy transfer microscopic parameter calculated with the Inokuti-Hirayama model gives a value of 240 × 10~(-40) cm~6 s~(-1), being one of the highest reported in the literature for Nd~(3+)-Yb~(3+) co-doped matrices. From the steady-state experimental absorption and emission cross-sections, a general expression for estimating the microscopic energy transfer parameter is proposed based upon the theoretical methods developed by Miyakawa and Dexter and Tarelho et al. This expression takes into account all the resonant mechanisms involved in an energy transfer processes together with other phonon-assisted nonvanishing overlaps. The value of the Nd~(3+)→Yb~(3+) energy transfer microscopic parameter has been calculated to be 200 × 10~(~40) cm~6 s~(-1), which is in good agreement with that obtained from the Inokuti-Hirayama fitting. These results show the importance of the nonresonant phonon-assisted Nd~(3+)→Yb~(3+) energy transfer processes and the great potential of these glasses as active matrices in the development of multiple-pump-channel Yb~(3+) lasers.