Power dependence of luminescence of Tb 3+-doped KYb(WO4) 2 crystal

Abstract

The effect of excitation intensity on luminescence properties of Tb 3+-doped KYb(WO 4) 2 crystal is reported. In particular, emissions following the Stokes and anti-Stokes excitations were investigated. It was found that, in addition to the Tb 3+ luminescence, an intense Yb 3+ luminescence at room temperature was observed after a direct excitation of Tb 3+ ions in spite of the fact that both ions are far off-resonance. The intensities of Tb 3+ and Yb 3+ luminescences were dependent on the excitation power and changed by a sublinear function (slope<1). The mechanism of the non-resonant energy transfer from Tb 3+ to Yb 3+ is discussed in terms of the phonon-assisted cross-relaxation and the down-conversion contributing to the process. The up-conversion emission of Tb 3+ (after a direct excitation of Yb 3+ ions) was observed at room temperature and its intensity varied with the slope <2. It was found that the emission decay times were strongly dependent on the excitation power. The mechanism of this behaviour is discussed in terms of many-body energy transfer.