BACK TRANSFER IN THE S-4(3 2) STATE OF CS2NAERXY1-XCL6 EXTENSION OF THE SHELL-MODEL/

The S-4(3/2) state of Er3+ in Cs2NaErxY1-xCl6 undergoes a cross relaxa tion above 100 K which involves a transition from the S-4(3/2) to the I-4(9/2) and I-4(3/2) states at the donor (D) and the excitation of th e acceptor (A) to the I-4(13/2), I-4(9/2) states. Analysis of experime ntal decay curves from the S-4(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 held levels means that the rate of back transfer from the acceptor to the d onor is comparable with or greater than the cross relaxation rate, and therefore must be included explicitly. The effect that inclusion of t he back transfer terms has on the decay of the S-4(3/2) State is exami ned numerically. We have simulated decay curves for the S-4(3/2) State within the shell model with inclusion of the back transfer terms. The se simulated curves are in good agreement with the experimental decay curves. (C) 1998 Elsevier Science B.V. All rights reserved.