Tb3+as probe ion—Clustering and phase separation in borate and borosilicate glasses

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AbstractVarious borate and borosilicate glasses doped with Tb3+ in a broad concentration range of 1 × 1018 to 1 × 1021 Tb3+ per cm3 (~0.01 to 10 wt% Tb2O3) were prepared and characterized by different methods. Static fluorescence excitation and emission spectra of Tb3+ 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 Tb3+ ions were detected. To identify these different local sites crystalline terbium borate, TbBO3, 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 Tb3+ ions were accumulated in the phase with higher optical basicity. The local sites of the Tb3+ ions in the clusters induce a short lifetime which is similar to the lifetime of crystalline TbBO3. Only mono‐exponential decay curves for Tb3+ fluorescence were detected in sodium borosilicate glass with high optical basicity, and in zinc borate glass, without tendency to phase separation.