HIGH-ORDER MULTIPOLE INTERACTION IN NANOSECOND ND-ND ENERGY-TRANSFER

The nanosecond energy transfer kinetics of the (4)G(7/2)+K-2(13/2) mul tiplet of the Nd3+ ion in the LaF3 laser crystal was investigated. The energy transfer rates of electronic excitation from donors (excited N d3+ ions) (D) to different coordination spheres of accepters (A) (unex cited Nd3+ ions) were determined considering no energy migration. The predominance of the dipole-quadrupole (dq) mechanism against dipole-di pole (dd) was found from the analysis of these rates for the donor-acc eptor distances from 6.05 Angstrom and up to 17 Angstrom. For the dist ances in the range from 4.1 to 4.4 Angstrom the mechanism of donor-acc eptor interaction differes from that for the longer donor-acceptor dis tances. It was shown that a high rate and predominance of the dipole-q uadrupole interaction is correlated with the larger value of the squar e of the low rank reduced matrix element U-(2) in comparison with thos e of the high rank U-(4) and U-(6) for one of the transition involved in the process of energy transfer. We point out that the dipole-dipole nonradiative energy transfer from the F-4(3/2) metastable level of Nd 3+ ion is usually realized because of the small values of (U((2)2)) in comparison with (U((4)2)) and (U((6)2)) for both transitions involved in the quenching process.