Multifunctional applications of Ho³⁺ doped Ca₂MgWO₆ phosphors: A comprehensive optical, structural, temperature sensing, and Judd-Ofelt analyses

Ho³⁺ doped Ca₂MgWO₆ phosphors were prepared via the solid-state reaction and systematically investigated to study their structural, optical, and multifunctional properties. XRD and Rietveld refinement confirmed the formation of a monoclinic double perovskite phase, while SEM analysis revealed irregularly shaped, micron-sized particles with uniform elemental distribution. Under 454 nm excitation, the phosphors exhibited intense green emission at 546 nm, along with weaker red (653 nm) and near-infrared (757 nm) bands, yielding CIE chromaticity coordinates in the green region with nearly 100 % colour purity. The optimum Ho³⁺ concentration was identified as 2 mol%, with quenching beyond this point governed by dipole-dipole interactions. Diffuse reflectance spectroscopy and Tauc's analysis indicated a direct band gap of 3.32 eV, and the Judd-Ofelt analyses revealed the covalent nature and significant distortion around Ho³⁺ sites. Temperature-dependent photoluminescence revealed a quenching temperature of 398.43 K. Temperature sensing behaviour was analyzed through polynomial fitting, demonstrating maximum relative sensitivities of 0.24 % K⁻¹ and 0.23 % K⁻¹ at 498 K. These results highlight Ca₂MgWO₆:Ho³⁺ as a robust candidate for optical thermometry and green LED applications.