Tb3+-impregnated,non-porous silica glass possessing intense green luminescence under UV and VUV excitation

A colorless transparent luminescence material was successfully prepared by impregnation of leached, porous glass with Tb³⁺ ions followed by reductive sintering in a CO atmosphere. Tb³⁺ emissions under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation clearly showed the most intense emission band to be situated at 543 nm, which corresponds to the ⁵D₄ → ⁷F₅ transition. Sintering of the Tb glass in a reducing atmosphere resulted in a significant enhancement of Tb³⁺ emission intensity in comparison with sintering in air. The presence of traces of cerium ions was verified in Tb glasses, and more Ce³⁺ ions were produced as a result of the reductive sintering. The increase in Ce³⁺ ions was believed to be mainly responsible for the enhancement of ⁵D₃ → ⁷F_j and ⁵D₄ → ⁷F_j transitions from Tb³⁺ ions owing to an energy transfer channel. A clearly defined difference in the spectral energy distribution of Tb³⁺ emissions was found for 231 nm UV and 160 nm VUV excitation of the Tb glass. The phenomenon of cross relaxation was only observed under 231 nm UV excitation. Different excitation mechanisms were taken into account. Direct excitation of Tb³⁺ ions together with Ce³⁺ ions occurred in the Tb glass under the 231 nm UV light, whereas indirect excitation consisting of host absorption of energy and transfer from host to Tb³⁺ ions occurred under the 160 nm VUV light.