An intense NIR emission at 1.57 mu m is reported in a newly synthesized Yb3+-Er3+ codoped Zinc-borobismuthate glasses. The energy transfer efficiency is found to be 78% for 1 mol% Yb2O3 and 0.5 mol% Er2O3 concentrations. The transfer process follows a static energy transfer mechanism at a low donor concentration (0.1 mol%); whereas, it gets accelerated by donor energy migration at 1 mol% Yb2O3. In this glass system, the energy back-transfer has found to be negligible from estimated critical interaction distances for direct (Yb3+ -> Er3+) and back (Yb3+ <- Er3+) energy transfer phenomena. The observed efficient NIR emission at 1.57 mu m has been explained based on the effective energy transfer from Yb3+ ions accompanied by rapid depopulation of I-4(11/2) excited level of Er3+ ions through non-radiative multi-phonon relaxation processes, which has also restricted the excited state absorption (ESA) from this level leading to no upconversion suggesting the potentiality of present glass host for proficient NIR luminescence. (c) 2012 Elsevier B.V. All rights reserved
