New NIR emission from Sm3+ in Yb3+-Sm3+ co-doped tellurite glass

Abstract

Yb3+, Sm3+ and Yb3+-Sm3+ doped tellurium oxide glasses were prepared. Their spectroscopic properties in the near-infrared region were studied. In the singly doped Sm3+ glass, excited by 403 nm, emission transitions occurred from the usual level 4G5/2 leading to strong fluorescence mainly in the visible range. In the co-doped Yb3+-Sm3+ glass Yb3+ donor ions were excited by 976 nm and transferred their energy by non-radiative processes to Sm3+ acceptor ions, promoting them to 6F11/2 and 6F9/2. Using an amplified spontaneous emission experiment, new emissions in Sm3+ from 6F11/2 and 6F9/2 were observed at 1080, 1240, 1435 and 1457 nm. These are the first reported emissions from these levels in Sm3+. The Yb3+ to Sm3+ energy transfer process was studied by measurement of the fluorescence decay curve of the Yb3+ donor. A diffusion model taking into account the migration of excitation amongst the Yb3+ donor ions was used to fit the decay curve and subsequently determine the donor-acceptor energy transfer microparameter CDA and the transfer parameter γ. The experimental values of these parameters were higher than those calculated by Dexter's model for resonant non-radiative transfer between donor and acceptor ions. These results demonstrate the importance of the non-resonant phonon-assisted Yb3+ to Sm3+ energy transfer processes in the tellurite glass. Energy transfer was efficient as evidenced by a large reduction in the Yb3+ lifetime in the Yb3+-Sm3+ glass compared to in the singly doped Yb3+ glass. The new emissions from Sm3+ were though of low fluorescent intensity. This was due to the high non-radiative decay rates of levels 6F11/2 and 6F9/2 by multi-phonon relaxation.