A novel high-sensitive optical thermometer based on the multi-color emission in Pr3+ doped LiLaMgWO6 phosphors

Highlights: • Double perovskite Pr³⁺: LiLaMgWO₆ phosphor is designed for FIR-based thermometry. • The emission color is dependent on doping concentration and temperature. • Two FIR models (FIR-I₆₁₆/I₄₉₆ and FIR-I₆₁₆/I₆₅₄) are constructed and studied. • The maximal absolute sensitivity is 2421 × 10⁻⁴ K⁻¹ at 573 K based on FIR-II. • FIR-II keeps a high relative sensitivity above 1% K⁻¹ in a wide temperature range (280 K). Nowadays, optical thermometric materials with high sensing sensitivity in a wide temperature interval are urgently required due to the appealing prospect in the field of sensing technology. Herein, the double perovskite Pr³⁺: LiLaMgWO₆ phosphors are successfully prepared via a high-temperature solid-state reaction method, and their concentration/temperature-dependent luminescence properties are discussed systematically. Upon UV excitation, the samples emit blue (³P₀→³H₄), green (³P₀,₁ → ³H₅) and red emissions (¹D₂→³H₄, ³P₀→³F₂) from Pr³⁺ ions. The different changing tendencies in relation to temperature are observed for the emissions from ³P₀ and ¹D₂ multiplets, which are attributed to the effects of cross-over process to Pr³⁺-W⁶⁺ intervalence charge transfer (IVCT) state, cross relaxation process and multiphonon relaxation process. When the fluorescence intensity ratio (FIR) between ³P₀→³F₂ (654 nm) and ¹D₂→³H₄ (616 nm) transitions is applied for temperature sensing, 0.5%Pr³⁺: LiLaMgWO₆ displays a maximum absolute sensing sensitivity of 2421 × 10⁻⁴ K⁻¹ at 573 K. Moreover, it can keep a comparatively high relative sensitivity (1%~3.25% K⁻¹) and low temperature uncertainty (0.15–0.5 K) over a wide temperature range (~280 K), which are superior to those of many luminescence materials reported previously. The present study may provide useful design information to develop high-sensitive luminescent thermometers with a wide applicable temperature range.