B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Беларусь

The dynamics of upconversion luminescence formation and decay in rare-earth ions (REIs) under conditions of significant cross-relaxation energy transfer are analyzed using three- and eight-level models. Numerical modeling is performed by solving systems of nonlinear rate equations for the populations of the relevant energy levels under various excitation schemes. The luminescence is examined for laser excitation of different intensities and pulse durations, as well as for a range of parameters characterizing the REIs and the efficiency of cross-relaxation. Analysis of the decay kinetics shows that the luminescence decay rate is governed by the nonlinear evolution of the upconversion process and can therefore be strongly nonexponential.