Luminescent, and thermometric properties of Er3+-activated NaCaGd(WO4)3 phosphor for solid-state lighting and thermal sensing

Abstract

We report the synthesis and comprehensive characterization of Er³⁺-doped NaCaGd(WO₄)₃ phosphors with dopant concentration (0–7%) via solid-state reaction methodology. Rietveld refinement of synchrotron X-ray diffraction data confirms a phase-pure tetragonal scheelite structure (I4₁/a) with successful lattice-tuned substitution of Gd³⁺ by Er³⁺ ions, with unit cell contraction indicating homogeneous incorporation. Morphological studies via scanning electron microscopy demonstrate uniform particle distribution with compact grain morphology. Luminescence analysis reveals vivid green emission (CIE: x = 0.337, y = 0.587) from ²H_11/2 and ⁴S_3/2 excited states, under 325 nm excitation. The material exhibits exceptional thermometric performance through non-contact fluorescence intensity ratio thermometry over 298–573 K, with Boltzmann-distributed thermal quenching behavior: relative sensitivity peaks at 1.55% K⁻¹ near ambient conditions, coupled with an absolute sensitivity of 1.81 × 10⁻² K⁻¹ and sub-kelvin thermal resolution (±0.15 K at 300 K), values competitive with state-of-the-art rare-earth thermophosphors. The combination of optical stability, tunable green emission from efficient host-sensitization, and sub-kelvin temperature discrimination positions NaCaGd(WO₄)₃:Er³⁺ as a bifunctional material for next-generation solid-state lighting, full-color display systems, and non-contact high-precision thermal sensing.