Tb3+ Fluorescence and Nonradiative Energy Transfer from Gd3+ to Tb3+ in Borate Glass

Abstract

The fluorescence behavior of Gd³⁺ and Tb³⁺ has been studied with the ions dissolved together in a Calibo‐1 glass host. The two ions form a coupled system so that energy absorbed by Gd³⁺ is transferred to Tb³⁺ by a nonradiative mechanism and is then emitted as Tb³⁺ fluorescence. When Tb³⁺ is incorporated alone into this glass, concentration quenching effects are observable. These have been found to be due to the shortening of the Tb^{3+ 5}D₄ lifetime, which in turn is due to the Tb³⁺ ions being packed closer together as the concentration of Tb³⁺ is increased. It is proposed that this gives rise to ``chains'' of Tb³⁺ ions along which energy can migrate, by a nonradiative transfer mechanism, to sinks in the structure. The rate of internal conversion from Tb^{3+ 5}D₃ to Tb^{3+ 5}D₄ has also been studied as a function of concentration. The results have been interpreted as being due to the formation of Tb³⁺‐Tb³⁺ resonance‐coupled pairs, which causes the rate of internal conversion to increase as the concentration of Tb³⁺ increases. The effects of changes in temperature and base glass composition on the Tb^{3+ 5}D₄ lifetime have also been investigated and are reported.