Radiative properties of green-emitting Ho³⁺ doped Y₂SiO₅ system: exploring the potential use as a phosphor

Y₂SiO₅ (YSO) phosphors doped with holmium ions were prepared by the well-established sol–gel method. The structural and functional groups were studied by X-ray diffraction (XRD) and Fourier-transformed infrared (FTIR) spectroscopy, respectively. The observed XRD peaks were matched to the X1 and X2 phase of YSO and the average crystalline size is found to be 26.5 nm. The band gap was calculated using Kubelka–Munk analysis of the diffuse reflectance data. Photoluminescence tests were carried out on the prepared phosphors. At an excitation wavelength of 447 nm, two sharp and closely spaced peaks are observed in the green region around 538 nm and 551 nm. The concentration quenching is observed beyond 0.03 mol Ho³⁺ ions in YSO and the energy transfer mechanisms are discussed in detail. Dexter’s analysis shows that the interaction between Ho³⁺ ions is dipole–dipole. The Judd–Ofelt intensity parameters and radiative properties of certain emission transitions of Ho³⁺ ions were also investigated for an optimized phosphor (Y₂SiO₅:0.03Ho³⁺) sample. The estimated J–O parameters (Ω_λ (λ = 2, 4 & 6)), are Ω₂ = 0.77 × 10^–20 cm², Ω₄ = 0.40 × 10^–20 cm² and Ω₆ = 2.12 × 10^–20 cm². The magnitude of Ω₂ is smaller for YSO than that of other hosts indicating a less asymmetric environment around the Ho–O bond. Branching ratio and stimulated emission for the ⁵F₄ + ⁵S₂ → ⁵I₈ transition are 87.8% and 2.61 × 10^–21 cm², respectively, for Y₂SiO₅:0.03Ho³⁺ phosphor. Furthermore, colorimetric analysis shows that the optimized Y₂SiO₅:0.03Ho³⁺ phosphor has the highest color purity. Our results confirm that these phosphors can be proposed for utilization as green components in solid-state lighting applications.