Negative thermal quenching and optically stable Tb3+-doped tungstate phosphor for high temperature lighting and advanced thermometry applications

Abstract

This study reports the anomalous temperature-dependent luminescence behaviour of Tb³⁺-doped Ca₂MgWO₆ double perovskite phosphors designed for multifunctional optical and temperature sensing applications. The optimized composition (6 mol% Tb³⁺) results in an unusual enhancement (∼242%) of the green emission intensity (⁵D₄ → ⁷F₅, 546 nm) with increasing temperature, which indicates negative thermal quenching. This phenomenon is attributed to the thermally stimulated carrier release from the defect complexes and their subsequent recombination at the luminescent centers. The optimized phosphor demonstrates excellent thermal stability and consistent luminescent performance in the green spectral region. Diffused reflectance revealed a direct band gap of approximately 3.24 eV and a refractive index near 2.33, supporting its wide-band-gap semiconducting nature. Fluorescence intensity ratio-based thermometric evaluation yields a maximum absolute and relative sensitivity of 1.46 × 10⁻⁴ K⁻¹ and 0.05% K⁻¹, respectively, highlighting its potential for efficient high-temperature optical sensing and lighting applications.