Formation probability of Cr-Nd pair and energy transfer from Cr to Nd in Y3Al5O12 ceramics codoped with Nd and Cr

Temperature dependence of decay curves of the Cr3+ and Nd3+ luminescence excited at 432 nm in the Cr3+ absorption bands for YAG ceramics codoped with 1 mol. % Nd3+ and 0.1 mol. % Cr3+ indicates two distinct energy transfer processes from Cr3+ to Nd3+: one is a temperature-independent process via the lowest 2E excited state of Cr3+ through the exchange interaction between Cr3+ and Nd3+ ions; the other is a temperature-dependent process via the higher 4T2 excited states of Cr3+ through the thermal Boltzmann distribution. In order to explain these results, we have proposed a simple model on energy transfer from Cr3+ to Nd3+, taking into account a formation probability of a Cr-Nd pair in YAG as a function of separation distance. This Cr-Nd pair model has estimated that the former and latter energy transfer processes occur from a Cr3+ ion to one of Nd3+ ions substituting for the first nearest neighbor Y3+ ions and near Y3+ ions beyond within a sphere with an approximate radius of less than 0.8 nm, respectively.