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

Abstract

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.