Power dependence of luminescence of Tb3+-doped KYb(WO4)2 crystal

The effect of excitation intensity on luminescence properties of Tb3+-doped KYb(WO4)2 crystal is reported. In particular, emissions following the Stokes and anti-Stokes excitations were investigated. It was found that, in addition to the Tb3+ luminescence, an intense Yb3+ luminescence at room temperature was observed after a direct excitation of Tb3+ ions in spite of the fact that both ions are far off-resonance. The intensities of Tb3+ and Yb3+ luminescences were dependent on the excitation power and changed by a sublinear function (slope<1). The mechanism of the non-resonant energy transfer from Tb3+ to Yb3+ is discussed in terms of the phonon-assisted cross-relaxation and the down-conversion contributing to the process. The up-conversion emission of Tb3+ (after a direct excitation of Yb3+ 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.