Tb ³⁺ as probe ion—Clustering and phase separation in borate and borosilicate glasses

Abstract Various borate and borosilicate glasses doped with Tb ³⁺ in a broad concentration range of 1 × 10 ¹⁸ to 1 × 10 ²¹ Tb ³⁺ per cm ³ (~0.01 to 10 wt% Tb ₂ O ₃ ) were prepared and characterized by different methods. Static fluorescence excitation and emission spectra of Tb ³⁺ in the ultraviolet‐visible range were recorded. The fluorescence decay rates of the green emission were measured and fitted. Different lifetimes dependent on different local sites of Tb ³⁺ ions were detected. To identify these different local sites crystalline terbium borate, TbBO ₃ , was prepared and investigated. X‐ray diffraction (XRD) and electron microscopy measurements were used. Very strong clustering effects of Tb ³⁺ ions were detected as preliminary stage of phase separation by formation of a very short decay rate in optically clear borate containing glasses with low optical basicity. In glass samples with phase separation, the Tb ³⁺ ions were accumulated in the phase with higher optical basicity. The local sites of the Tb ³⁺ ions in the clusters induce a short lifetime which is similar to the lifetime of crystalline TbBO ₃ . Only mono‐exponential decay curves for Tb ³⁺ fluorescence were detected in sodium borosilicate glass with high optical basicity, and in zinc borate glass, without tendency to phase separation.