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 Y0.97VO4:0.03Ho3+ phosphors were used to obtain the total transition probabilities (AT), radiative lifetimes (τrad) 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 σP(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 Y0.97VO4:0.03Ho3+ phosphor. The estimated color coordinates were observed in the green region of CIE diagram. Ultimately, the superior properties (σP(λ), β, and color purity) of Y0.97VO4:0.03Ho3+ phosphor may make it suitable for green emitting devices.