Optical tunability and higher order polynomial parameterization of the temperature dependent emission in Sm³⁺/Eu³⁺ co-activated tungstate phosphors for optoelectronic applications

Phosphor based colour-tunable materials and optical temperature sensors have attracted considerable attention due to their non-contact temperature detection capabilities and optoelectronic applications. In this work, Ca₂MgWO₆:1.25 mol% Sm³⁺, xEu³⁺ (x = 0–16 mol%) phosphors were synthesized via a solid-state reaction route. Under 409 nm excitation, efficient energy transfer from Sm³⁺ to Eu³⁺ ions enabled strong spectral tunability, with an optimal Eu³⁺ concentration of 10 mol% beyond which concentration quenching occurred through dipole-quadrupole interactions. The optimized phosphor showed a direct optical band gap of 3.34 eV and retained 47 % of its emission intensity at 498 K, indicating high thermal stability. The activation energy (0.21 eV) and quenching temperature (393 K) confirmed excellent thermal robustness. Temperature-dependent luminescence analysis using a 4th order polynomial fit yielded maximum absolute and relative sensitivities of 0.0432 K^-1 and 0.29 % K⁻¹ at 298 K, demonstrating strong potential for solid-state lighting and optical temperature sensing applications.