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

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 (4)G(5/2) 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 F-6(11/2) and F-6(9/2). Using an amplified spontaneous emission experiment, new emissions in Sm3+ from F-6(11/2) and E-6(9/2) 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 CPA and the transfer parameter y. The experimental values of these parameters were higher than those calculated by Dexter's model for resonant nonradiative transfer between donor and acceptor ions. These results demonstrate the importance of the nonresonant 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 F-6(11/2) and E-6(9/2) by multi-phonon relaxation.