MANY-BODY ENERGY-TRANSFER PROCESSES BETWEEN ER-3+ IONS IN YTTRIUM-ALUMINUM-GARNET

The results of the luminescence-quenching measurements of the 4S3/2 level of Er3+ in yttrium aluminum garnet are reported. Decay data in a large temperature (10-300 K) and concentration range (0.1-100 at.%) are analyzed. The quenching process depends strongly on concentration and temperature. At low Er3+ content (3 at.%) the quenching is dominated by two-ion dipole-dipole cross-relaxation processes. It is shown that the previous proposed mechanisms can only explain the high-temperature data, and a possible active mechanism at low temperatures is proposed. At higher concentrations the quenching process depends strongly on temperature, the migration on donors playing an essential role, especially at low temperatures, where the supermigration regime is observed. The quadratic concentration dependence of the transfer parameters at high Er3+ content is connected with the three-ion cross-relaxation processes. The temperature dependences of the supermigration rates are consistent with two types of three-ion processes, i.e., one phonon-assisted process at low temperatures (T<100 K) and another very efficient resonant one [(4S3/2,2H11/2)4I15/2]D+[(4I15 4/2I13/2)A1+(4I15/24I9/2)A at high temperatures (T>150 K). It is shown that at 300 K for C>10 at.% Er3+ the transfer is of direct donor-acceptor type, due to the above cross relaxation. Thus, at 300 K, the energy from the pumping 4S3/2 level is transferred to the 3-m laser levels (4I11/2 and 4I13/2) by a three-ion cross relaxation. This study has emphasized the possibility of very efficient three-ion processes in the luminescence quenching of rare earth elements at large activator concentrations. © 1990 The American Physical Society.