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

Abstract

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 (VO₄³⁻) 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 Ω₂ = 0.03 × 10⁻²⁰ cm², Ω₄ = 0.22 × 10⁻²⁰ cm², and Ω₆ = 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.