THEORETICAL MANIFESTATION OF THE SHELL-MODEL FOR ENERGY-TRANSFER

Luminescence decay curves for the (4)G(5/2)-->H-6(7/2) emission of Sm3 + in the hexachloroelpasolite crystals Cs2NaSm0.01Gd0.99Cl6 and Cs2NaS m0.01Eu0.1Y0.89Cl6 have been measured over the temperature range 10-30 0 K using pulsed laser excitation into the magnetic-dipole allowed H-6 (5/2)-->(4)G(5/2) electronic transition of Sm3+. The emission is quenc hed by cross relaxation to nearby Sm3+ ions and energy transfer to the D-5(0) State of Eu3+ accepters and the decay curves are analyzed usin g a recently developed shell model for energy transfer. The correspond ing energy-transfer rate to a single Eu3+ acceptor at a distance R-1 = 7.65 Angstrom shows a rapid increase in the temperature range 200-300 K which is explained in terms of the thermal population of the initia l Sm3+((4)G(5/2))Gamma(7) donor state and the Eu3+(F-7(1))Gamma(4) acc eptor state. The near-resonant magnetic dipole-magnetic dipole contrib ution to the total energy-transfer rate between a Sm3+ donor ion and a nearest-neighbour Eu3+ acceptor is calculated. We show the applicabil ity of the shell model for the simultaneous treatment of cross-relaxat ion and energy-transfer processes to the (4)G(5/2) decay kinetics of S m3+ in a cubic lattice. (C) 1998 Elsevier Science B.v. All rights rese rved.