Energy transfer processes in Yb3+ and Tm3+ ion-doped fluoride crystals

Energy transfer processes from Yb3+ to Tm3+ ions have been investigated in various fluoride microcrystals to examine the application limit of a simple rate equation model and to obtain methods for characterizing the host materials as to energy transfer. It has been shown that the energy transfer coefficients from donor Yb3+ to acceptor Tm3+ ions differ by nearly one order of magnitude even for fluoride lattices that have similar luminescence characteristics. The energy transfer coefficients increase monotonically with Yb3+ concentration at low Yb3+ concentrations, while they take nearly constant values at high Yb3+ concentrations. The present experimental results were compared with computer simulation results as well as related analyses. It is shown that the apparently complicated behaviors are consistently explained by a microscopic model. As an example of the application of the present results, the optimization of the infrared emission of Tm3+ ions is shown. (C) 1999 American Institute of Physics. [S0021-8979(99)01508-X].