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A study of the quantum efficiency of the luminescence of gadolinium and terbium in borate glasses and of the energy transfer between these ions is presented. From our measurements of fluorescence decay times, absorption, fluorescence, and excitation spectra, we calculated the fluorescence quantum yield of the 6P7/2 gadolinium and the 5D4 terbium levels on excitation to higher gadolinium and terbium levels, respectively. The energy transfer rates between gadolinium and terbium in borate glasses were calculated on the basis of the above measurements. These measurements were performed for gadolinium and terbium concentrations ranging from 0 to 4 wt%. Our results show that the energy transfer occurs mainly between the 6P7/2 gadolinium level and (5D0, 5H7) terbium levels and is due to a dipole-dipole interaction. It is concluded that the energy transfer between gadolinium and terbium is a phonon assisted process.

Submicron size spheres of silica and alumina prepared by well-known methods were coated sonochemically by nanoparticles of oxides of europium and terbium using the same concentration of ions. We have also used sonochemistry to prepare nanoparticles of silica and alumina doped by the same rare-earth ions for comparison. The highest luminescence intensities were observed for europium and terbium doped in nanoparticles of alumina of dimension 20-30 nm. The intensities are comparative or higher than in commercial phosphors.