[en] Study of energy transfer from optically excited Eu³⁺→Ho³⁺ has been carried out in calibo glass. Probabilities and efficiencies of energy transfer from Eu³⁺→Ho³⁺ have been calculated from the life time and emission intensity of Eu³⁺+Ho³⁺. At low acceptor concentrations Psub(da) varies linearly with Csub(a) showing migration of energy among donors. At high acceptor concentrations Psub(da) depends linearly on (Csub(a)+Csub(d))², which is inconsistent with Fong and Diestler's theory of dipole-dipole mechanism of energy transfer. At low temperature emission intensity and life time increase, decreasing probability (Psub(d)) and efficiency (etaT) suggesting at room temperature the energy is transferred to the lattice by donor lowering life time and intensity. At high temperature no emission from higher levels of the donor is obtained suggesting blurred energy levels in the glass matrix. (Auth.)

[en] Non-radiative energy transfer from optically excited Tb³⁺ to Ho³⁺ has been studied in calibo glass. An experimental investigation has been made into the nature of the decay of excited Tb³⁺ donors in the presence of Ho³⁺. The time dependence of luminescence decay following pulsed excitation illustrates the transient fluorescence behaviour characteristic of diffusion-limited relaxation. The data are analysed to determine the probability for Tb³⁺ to Ho³⁺ energy transfer, and the critical transfer distance for energy exchange. The results imply that the mechanism of donor-acceptor energy transfer is based on electric dipole-dipole interaction. An investigation is also carried out at 80 K on excitation decay whose probability changes suddenly and in a non-correlated manner as a result of migration over randomly distributed centers, that interact with each other more strongly than they do with the acceptors. (Auth.)