Optical characterization and defect-induced behavior in ZnAl_1.999Ho_0.001O₄ spinel: Unraveling novel insights into...

The ZnAl_1.999Ho_0.001O₄ phosphor, prepared by the solid-state method, crystallizes in the cubic spinel structure. Morphology and chemical composition homogeneity were determined via Energy Dispersive X-ray and SEM analysis. The (E_g) optical band gap was evaluated from the UV/vis absorption spectrum, confirming direct transition behavior according to Tauc's law. The Urbach energy (Eu) in the ZnAl_1.999Ho_0.001O₄ spinel was higher than that in the ZnAl₂O₄ spinel, indicating increased disorder and a higher concentration of defects due to Ho³⁺ ions. The penetration depth (δ(λ)), optical extinction (k(λ)), and refractive index (n(λ)) were assessed across wavelengths (λ). The room temperature absorption spectrum revealed several peaks corresponding to the 4f-4f transitions of Ho³⁺ ions.