Terbium-doped transparent glass-ceramics containing TbPO4 crystals: A promising material for photonic applications

Abstract

Glasses and glass-ceramics based on the Tb³⁺-doped SbPO₄-GeO₂-Al₂O₃ composition have been studied. Samples containing up to 0.4 mol % of Tb₄O₇ form glasses when obtained by melt-quenching while concentrations above that tends to form glass-containing single crystals. This work reports the thermal, structural, morphological, and optical studies of (96-x)(40SbPO₄-60GeO₂)-4Al₂O₃-xTb₄O₇ samples (where 0.2 ≤ x ≤ 0.7, in mol %) using Differential Scanning Calorimetry, X-ray Powder Diffraction, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, UV–Vis absorption, Raman, and Photoluminescence spectroscopies. The diffraction pattern for the glass-ceramic containing 0.7 mol% of Tb₄O₇ shows diffraction peaks, which were assigned to the crystalline phase derived from terbium orthophosphate (TbPO₄). In the same direction, the Raman spectra of the glass-ceramics containing 0.5, 0.6, and 0.7 mol% of Tb₄O₇ exhibited narrow bands in the region between 900 and 1300 cm^-1, which are characteristic of the main vibrational modes of the PO₄ tetrahedral units of TbPO₄. The TbPO₄ crystals exhibited an average size distribution ranging from 10 to 200 μm. The TbPO₄ crystals exhibited an unusual morphology and design, resembling the shape of the letter "H" and is completely different from the crystals reported in the literature. Strong green emission from TbPO₄ crystals was verified at 547 nm for all samples. The emission spectra showed not only bands assigned to ⁵D₄→⁷F_J electronic transitions in the green-red range, but also those coming from ⁵D₃→⁷F_J in blue region.