Self-activated luminescent properties of zinc metaphosphate glasses enhanced by Tb3+ and Eu3+ doping for color tunability

Self-activated zinc metaphosphate (ZnP) glasses co-doped with Eu₂O₃ and/or Tb₄O₇, corresponding to the formula xEu₂O₃∙0.2Tb₄O₇∙(49.8-x)ZnO∙50P₂O₅ (x = 0, 0.2, 0.4, 0.6 mol%), were synthesized using the melt quenching technique. X-ray diffraction (XRD) confirmed the amorphous nature of all the prepared glasses. Fourier Transform Infrared (FTIR) spectroscopy revealed the characteristic metaphosphate network structure, which remained largely unchanged upon doping with Eu₂O₃ and/or Tb₄O₇. Under the UV-light illumination, ZnP glass exhibited intrinsic blue emission centered around 450 nm under UV excitation, which is attributed to intrinsic defects. Furthermore, the doped ZnP with Tb₄O₇ or Eu₂O₃ resulted in the characteristic green and red emissions due to the ⁵D₄ → ⁷F_J transitions of Tb³⁺ and ⁵D₀ → ⁷F_J transitions of Eu³⁺, respectively. In contrast, the co-doped ZnP with Eu₂O₃ and Tb₄O₇ resulted in yellow color emission. The UV–Visible, excitation, and photoluminescence spectra of the prepared matrices demonstrated efficient energy transfer from the self-activated ZnP host matrix to the Tb³⁺ and Eu³⁺ ions, as well as energy transfer from Tb³⁺ to Eu³⁺ ions. By adjusting the Eu³⁺ concentration and the excitation wavelength, the emission color could be precisely tuned across the green-white-red spectrum. CIE 1931 chromaticity coordinates confirmed the color tunability, shifting from green (0.253, 0.514) towards white (0.335, 0.428) and further towards red under different excitation conditions and doping levels. These results suggest that Tb³⁺/Eu³⁺ co-doped ZnP glasses are promising candidates for developing color-tunable phosphors for solid-state lighting applications.