From structure to luminescence investigation of oxyfluoride transparent glasses and glass-ceramics doped with Eu3+/Dy3+ ions

Glasses and glass-ceramics with nominal composition 73 TeO₂– 4BaO– 3Bi₂O₃–18SrF₂-2RE₂O₃ (where RE = Eu, Dy) have been synthesized by conventional melt-quenching technique and subsequent heat treatment at 370 °C for 24 h in air atmosphere. Various Eu³⁺ to Dy³⁺ molar ratio have been applied to investigate luminescence properties in both glass and glass-ceramic matrices. Especially, white light emission through simultaneous excitation of Eu³⁺ and Dy³⁺ has been studied in detail. Influence of crystalline SrF₂ phase on luminescence kinetics has been determined by luminescence decay time measurements. Presence of crystalline SrF₂ phase has been confirmed by X-ray diffraction technique XRD and transmission electron microscopy TEM. X-ray photoelectron spectroscopy XPS and Fourier-transform infrared spectroscopy FTIR have been applied to get further insight into structural properties of glass and glass-ceramic materials. Color tunable white light emission has been obtained using UV excitation. Influence of the SrF₂ crystallization on luminescence properties of prepared materials have been described in detail. Moreover, luminescence properties and especially emission color dependence on the Eu³⁺ to Dy³⁺ molar ratio have been exhaustively studied. Color-tunable white light emission has been observed as a result of simultaneous radiative transition of both, Eu³⁺ and Dy³⁺ ions when applying UV excitation. Judd – Ofelt and other optical parameters have been calculated based on luminescence emission spectra. Achieved results confirm that tellurite glass-ceramics containing SrF₂ nanocrystals are good hosts for RE³⁺ ions and they can be considered as new phosphors for white light emitting diodes WLEDs.