INTERACTION MECHANSISMS IN THE Bi^{3 +} -Eu^{3 +} ENERGY TRANSFER IN GERMANATE GLASS AT LOW TEMPERATURE.

The mechanisms of low temperature (T equals 4 K) energy transfer between Bi**3** plus and Eu**3** plus in germanate glass were studied under pulsed nitrogen laser excitation by selecting the emission from a subset of ions in the **3P yields **1S//O band which is broadened by inhomogeneity in the glass. The decay curves of the emission from the Bi**3** plus **3P//O state were obtained for various concdntrations of acceptor ions Eu**3** plus . There is no indication of diffusion of the excitation energy within the donor system. The experimental curves were fitted to Inokuti and Hirayama's equation. The best fit was obtained with a dipole-dipole interaction for the 0. 8%Bi**3** plus plus 0. 7%Eu**3** plus doped glass and with a quadrupole-dipole interaction for the 0. 8%Bi**3** plus plus 5%Eu**3** plus doped glass.