Luminescence of Tb 3+ ions in silicate glasses

Abstract

The optical absorption and photoluminescence emission spectra of terbium doped sodium and lithium aluminium silicate glasses have been measured as a function of terbium concentration. Optical absorption has been measured over the wavelength range from 250 nm to 40 μm and the absorption bands attributed to Tb 3+ ions have been identified. Luminescence emission occurs in two groups of bands in the blue and in the green. The green 5D 4 → 7F J emission is more intense than the blue 5D 3 → 7F J . The green luminescence is enhanced at the expense of the blue when the Tb 3+ ion concentration reaches 0.5 molar%, which corresponds to an ion separation of 20 Å. The green emission is quenched when the Tb 3+ ion concentration exceeds 5 molar%, corresponding to an ion separation of 9.5 Å. It is concluded that energy transfer from 5D 3 to 5D 4 levels begins at Tb 3+ ion separations of 20 Å, and that the process is multipolar. Exchange dipole processes set in at 9.5 Å and quench the green emission. The ion separations at which the two processes occur in silicate glasses are much larger than those at which similar processes set in crystalline material. This enhancement of energy transfer processes in silicate glass is attributed to inhomogeneous broadening of the absorption and emission bands. The detailed structure of the emission bands, particularly that of the 5D 4 → 7F 6,5,4 doublets, is used to suggest that the Tb 3+ ions occupy two different sites with rhombohedral and cubic symmetries.