Dy³⁺ ions doped (Na₂O/NaF)-Gd₂O₃–P₂O₅ glasses for solid state lighting material applications

Oxide and oxyfluoride glasses doped with Dy³⁺ ions were prepared by melt-quenching method with glass matrix 17Na₂O: 17Gd₂O₃: 65P₂O₅:1Dy₂O₃ and 17Na₂O: 17Gd₂O₃: 65P₂O₅:1Dy₂O_3. The work emphasizes the effect of fluoride and oxide content in the glass and its cause for photoluminescence and their physical properties. Oxide glass show higher density, molar volume and refractive index values than compared to oxyfluoride glass. Judd-Ofelt (JO) theory was employed to understand the oscillator strength of particular transition observed in absorption spectra in UV–Vis–NIR ron. Judd-Ofelt theory provides information on JO parameters such as Ω_λ (λ = 2,4,6) which shows Ω₂ > Ω₄ > Ω₆ trend for both these oxide and oxyfluoride glasses. The luminescence properties were studied for 574 nm (⁴F_9/2 → ⁶H_13/2) emission peak by exciting at appropriate wavelength (349 nm for corresponding to (⁶H_15/2 → ⁶P_7/2) and investigating radiative properties for other emission peaks observed from the spectra using JO parameters. The emission spectra, showed two major peaks corresponding to 482 nm blue emission (⁴F_9/2 → ⁶H_15/2) and 574 nm yellow emission (⁴F_9/2 → ⁶H_13/2). Stimulated emission cross section (σ) shows higher value for ⁴F_9/2 → ⁶H_13/2 transition for oxide and oxy-fluoride glasses, whereas oxyfluoride glass surpasses oxide glass. Similarly the emission intensity of oxyfluoride glasses show higher than oxide when monitored for Gd³⁺ ions (275 nm) and Dy³⁺ ions (349 nm). The experimental lifetime shows 0.539 ms and 0.540 ms for oxide and oxyfluoride glass sample, respectively. The x, y color coordinates under 349 nm excitation wavelength were (0.38, 0.43) for both glass samples. The Y/B ratio results suggests that the Gd³⁺ shows more covalency than compared to Dy³⁺ ions in the oxide glass whereas vice-versa in case of oxyfluoride glass hence, higher emission intensity at 574 nm. The data obtained from these investigations confirms that the present Dy-doped oxide and oxyfluoride glasses could be potential candidate for efficient luminescence materials for solid-state lighting applications, especially for white LEDs.