Back transfer in the 4S 3/2 state of Cs 2NaEr xY 1− xCl 6: extension of the shell model

Abstract

The 4S 3/2 state of Er 3+ in Cs 2NaEr x Y 1− x Cl 6 undergoes a cross relaxation above 100 K which involves a transition from the 4S 3/2 to the 4I 9/2 and 4I 3/2 states at the donor (D) and the excitation of the acceptor (A) to the 4I 13/2, 4I 9/2 states. Analysis of experimental decay curves from the 4S 3/2 state for x=0.001−1 using the standard shell model for energy transfer in the elpasolite lattice has not been successful. In this system the energies of the crystal field levels means that the rate of back transfer from the acceptor to the donor is comparable with or greater than the cross relaxation rate, and therefore must be included explicitly. The effect that inclusion of the back transfer terms has on the decay of the 4S 3/2 state is examined numerically. We have simulated decay curves for the 4S 3/2 state within the shell model with inclusion of the back transfer terms. These simulated curves are in good agreement with the experimental decay curves.