Optical transitions and radiative properties of green emitting Ho³⁺:YVO₄ phosphor

The Ho³⁺-doped YVO₄ phosphors were successfully prepared via a sol-gel process in which citric acid was used as a chelating agent. X-ray diffraction (XRD) confirmed the effective inclusion of Ho³⁺ ions into the host matrix with the formation of single phase YVO₄. The surface morphology was observed using SEM, the results of which showed a grain growth propensity and the agglomeration of prepared phosphors. The V-O (VO₄ ^3-) vibration mode was analyzed through Fourier transform infrared (FTIR) spectra. The spectroscopic properties were reported through UV-vis-NIR diffuse reflectance and photoluminescence (PL) spectra. The Judd-Ofelt (J-O) intensity parameters Ω ₂ = 0.03 × 10^-20 cm², Ω ₄ = 0.22 × 10^-20 cm², and Ω ₆ = 0.23 × 10^-20 cm² obtained for the Y_0.97VO₄:0.03Ho³⁺ phosphors were used to obtain the total transition probabilities (A _T), radiative lifetimes (τ _rad) and branching ratios (β) for the certain transitions of Ho³⁺ ions. Under 310 nm UV excitation, the visible emission spectra were measured, and an intense emission was observed around 541 nm (green region) for all the samples. The emission cross-section σ _P(λ) was 3.22 × 10^-21 cm² and the branching ratio (β) was 0.816; these were investigated to capture the optimal concentration of the Y_0.97VO₄:0.03Ho³⁺ phosphor. The estimated color coordinates were observed in the green region of CIE diagram. Ultimately, the superior properties (σ _P(λ), β, and color purity) of Y_0.97VO₄:0.03Ho³⁺ phosphor may make it suitable for green emitting devices.