Simultaneously tuning the luminescent color and realizing an optical temperature sensor by negative thermal expansion in Sc2(WO4)3:Tb/Eu phosphors

Abstract

At present, many researchers are focusing on trivalent lanthanide (Ln³⁺)-doped thermally enhanced upconversion luminescent (UCL) materials with negative thermal expansion (NTE) properties. However, selective anti-thermal quenching downshifting emissions of the activator and thermal quenching of the sensitizer in a phosphor with NTE properties are not implemented. Herein, Tb³⁺/Eu³⁺ co-doped Sc₂(WO₄)₃ phosphors synthesized by the solid-state method are explored in selectively enhanced red emission (Eu³⁺:⁵D₀ → ⁷F₂) due to the energy-transfer efficiency from Tb³⁺ to Eu³⁺ and the promoted radiative transition probability. The selective thermally quenched green emission (Tb³⁺:⁵D₄ → ⁷F₅) is owing to the change of energy transfer from Tb³⁺ to Eu³⁺ as the temperature increased. Moreover, under ultraviolet 365 nm excitation, the thermally stimulated color emission tuned from yellow to red with the increase in temperature. Based on the radically different thermal response downshifting the luminescence of the activator and sensitizer, the luminescence intensity ratio (LIR) of non-thermally coupled levels (NTCLs) for ⁵D₀ (Eu³⁺) and ⁵D₄ (Tb³⁺) is adopted for optical temperature sensing. The optimal relative sensitivity of temperature sensing in the Sc₂(WO₄)₃:25%Tb³⁺/3%Eu³⁺ sample could reach 2.94% K⁻¹ at 347 K. All these indicate that this Sc₂(WO₄)₃:Tb³⁺/Eu³⁺ material is a promising candidate for high-sensitivity optical temperature sensing.