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

At present, many researchers are focusing on trivalent lanthanide (Ln(3+))-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 Sc-2(WO4)(3) phosphors synthesized by the solid-state method are explored in selectively enhanced red emission (Eu3+:D-5(0) -> F-7(2)) due to the energy-transfer efficiency from Tb3+ to Eu3+ and the promoted radiative transition probability. The selective thermally quenched green emission (Tb3+:D-5(4) -> F-7(5)) 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 D-5(0) (Eu3+) and D-5(4) (Tb3+) is adopted for optical temperature sensing. The optimal relative sensitivity of temperature sensing in the Sc-2(WO4)(3):25%Tb3+/3%Eu3+ sample could reach 2.94% K-1 at 347 K. All these indicate that this Sc-2(WO4)(3):Tb3+/Eu3+ material is a promising candidate for high-sensitivity optical temperature sensing.