Upconversion luminescence and temperature sensing characteristics of Na0.5Mg0.5Sc1.5(WO4)3:Er3+/Yb3+ phosphors

Abstract

NASICON-type compounds are generally assumed to be promising candidates for both electrode and solid electrolyte materials; however, recent studies have also revealed their potential as efficient optical hosts. In the present work, Er³⁺/Yb³⁺ codoped Na_0.5Mg_0.5Sc_1.5(WO₄)₃ powders have been prepared by a conventional high temperature solid state reaction method. According to X-ray powder diffraction data, the synthesized tungstates crystallize in the NASICON structural type (S.G. Rc). The thermal expansion behavior is anisotropic: it exhibits negative expansion along the a and b axes, while showing positive expansion along the c axis, and the overall volume expansion is also positive. Under 980 nm laser diode excitation, the Na_0.5Mg_0.5Sc_1.5(WO₄)₃:Er³⁺/Yb³⁺ phosphors exhibit intensive upconversion luminescence. The observed emission lines are associated with ²H_9/2 → ⁴I_15/2 (403–418 nm), ²H_11/2 → ⁴I_15/2 (515–538 nm), ⁴S_3/2 → ⁴I_15/2 (538–565 nm) and ⁴F_9/2 → ⁴I_15/2 (647–676 nm) transitions in Er³⁺ ions. It has been found that the Na_0.5Mg_0.5Sc_1.45Yb_0.03Er_0.02(WO₄)₃ sample exhibits the highest luminescence intensity. The temperature sensing performance of the Na_0.5Mg_0.5Sc_1.45Yb_0.03Er_0.02(WO₄)₃ phosphor has been studied. The maximum values of absolute (relative) sensitivities are 0.98% × K⁻¹ (1.09% × K⁻¹) and 3.62% × K⁻¹ (0.65% × K⁻¹) when the I_{515–538 nm}/I_{538–565 nm} and I_{515–538 nm}/I_{647–676 nm} ratios are used as temperature dependent characteristics. The obtained results indicate that the studied phosphors are promising for applications in thermal sensors.