Synthesis and Characterization of Er ³⁺ -Doped SrNb ₂ O ₆ Phosphor for FIR Based Thermometer

A new optical thermometer material—Er ³⁺ -doped SrNb ₂ O ₆ —based on the fluorescence intensity ratio was synthesized and investigated by both theoretical calculation and experimental measurement, combining X-ray diffractometry (XRD), XRD Rietveld refinement, scanning electron microscopy, X-ray photon emission spectroscopy, photoluminescence (PL) and PL excitation of qualitative and quantitative analysis, to develop a novel green-emitting phosphor with excellent thermometry sensitivity. The Er ³⁺ ions occupied 4e sites of SrNb ₂ O ₆ , and the stable activator occupation induces luminescence properties of emissions at 525, 531, and 550 nm. The SrNb ₂ O ₆ : Er ³⁺ phosphor possesses an outstanding thermal sensitivity in the measurement region of 298–523 K, where S _a and S _r can achieve 6.15 × 10 ⁻³ K ⁻¹ and 1093.2711/T ² , respectively, at 323 K. The optical thermal properties originated from the thermal excitation and formation of quashing thermal equilibrium between ² H _11/2 and ⁴ S _3/2 levels, leading to photons on ⁴ S _3/2 → ⁴ I _15/2 transfer process thermally populate onto ² H _11/2 → ⁴ I _15/2 transfer process. This work will lay a foundation for further exploration of activator suitability in columbite phosphors, making it practicable to foreseeably improve thermal sensitivity and PL for emergent applications in optical thermometer.