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 St okes and anti-Stokes excitations were investigated. It was found that, in a ddition to the Tb3+ luminescence, an intense Yb3+ luminescence at room temp erature 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 sub linear function (slope < 1). The mechanism of the non-resonant energy trans fer from Tb3+ to Yb3+ is discussed in terms of the phonon-assisted cross-re laxation and the down-conversion contributing to the process. The up-conver sion 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 fo und 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. (C) 2001 Elsevier Science B.V. All rights reserved.