Composition effects on optical properties of Tb3+-doped heavy germanate glasses

A group of terbium-doped heavy germanate glasses were studied. Glass matrices contained GeO2, Gd2O3, BaO, and/or La2O3 with the Tb3+ doping concentration ranging from 1 to 5 mol%. The transmission and radioluminescence spectra were measured and their correlations with glass composition are discussed. It is found that the UV cut-off edge of glass matrices is related to the content of the network modifier BaO as well as to the mixed rare earths effect, while the concentration of trapping sites existing in the glass network is essential to the radioluminescence properties of the glass. The latter is also associated with the content of the network modifier BaO that produces unsaturated nonbridging oxygens; in the glass lattice. Another important mechanism influencing the luminescence process involves the enhanced energy transfer from Gd3+ ions to Tb3+ emission centers. A self-sensitizing effect of Tb3+ is observed in the Tb3+ concentration rani e studied, which contributes to some extent to the enhanced Tb3+ green emission. La2O3 additions to the host glass play an active role of partitioning Tb3+ in the glass matrix, thereby showing an enhanced blue emission because of the reduced cross-relaxation probability between Tb3+ cations.