Structural and luminescent properties of Er3+-doped tellurite-phosphate oxide/oxyfluoride glasses and glass-ceramics modified with Sr2+

In this study, tellurite-phosphate glasses and transparent glass-ceramics (GCs) in the oxide TeO2–P2O5–BaO–SrO–ZnO–Na2O–Er2O3 and oxyfluoride TeO2–P2O5–BaF2–SrF2–ZnF2–Na2O–Er2O3 systems were investigated. The effect of BaO/SrO and BaF2/SrF2 molar ratios on the structure and luminescent properties of the synthesized glasses and GCs was analyzed. The amorphous nature and thermal stability of the parent glasses were studied by X-ray diffraction (XRD) technique and differential thermal analysis (DTA). As assessed from the Fourier transform infrared (FTIR) spectra, the network of the oxide and oxyfluoride glasses was primarily composed of Te(F)O4, Te(F)O3, Te(F)O3+1, and phosphate Q0, Q1, Q2 units. The addition and increase in SrO/SrF2 content promoted depolymerization of the oxide and oxyfluoride tellurite-phosphate parent glass networks. Upon heat-treatment, controlled crystallization occurred in the flexible glasses network with many broken bonds due to SrO/SrF2 addition, resulting in the nucleation and growth of BaSrEr3O8 (∼75 nm) and Ba4Er3F17 (∼85 nm) nanocrystals. The crystallization mechanisms were driven by the initial structural depolymerization of network of parent glasses and the mobility of nucleating agents during heat-treatment, facilitated by the presence of SrO/SrF2. Incorporation of the erbium (Er3+) ions into the nanocrystals caused increased emission of Er3+ ions in transparent GCs compared to that in the parent glasses. This research contributes to the understanding of the relationship between composition, structure, and luminescent properties in tellurite-phosphate glasses and GCs. The findings highlight the potential of adjusting molar ratios of BaO/SrO and BaF2/SrF2 to enhance the luminescence of GC materials doped with erbium ions compared to parent glasses, which could be valuable for applications in optics and photonics.