Energy transfer and frequency upconversion in Yb 3+, Er 3+ co-doped sodium–lead–germanate glasses

Abstract

Yb 3+–Er 3+ co-doped Na 2O–GeO 2–PbO glass suitable for developing optical fiber lasers and amplifiers has been fabricated. The energy transfer efficiency from Yb 3+ to Er 3+ was investigated in the glasses with different Yb 3+–Er 3+ concentration ratios and the maximum energy transfer efficiency was found to be 67% at the Yb 3+–Er 3+ concentration ratio of 5:1. Subsequently, the studies of upconversion emissions in the visible range were performed. An intense green together with a relatively weak red emission was observed under the excitation of 976 nm diode laser. The quadratic dependence of the green emission on excitation power indicates that a two-photon absorption process occurs under a 976 nm excitation. However, for the red emission the slope of log-log plot of integrated intensity versus pump power declines with increasing Yb 3+ ions content, indicating it is not resulted from a biphotonic process.