Frequency upconversion based thermally stable molybdate phosphors in a temperature sensing probe

Abstract

Er³⁺–Yb³⁺ co-doped NaGd(MoO₄)₂ phosphors with different concentrations of Er³⁺ and Yb³⁺ ions have been successfully synthesized via a high-temperature solid-state reaction method. Phase confirmation and morphological studies have been done with the help of XRD and FESEM, respectively. The suitability of being a good host material with a high refractive index has been confirmed by the diffuse reflectance study. Intense green upconversion (UC) emission has been witnessed even with the naked-eye under a relatively low pump power of a 980 nm CW diode laser excitation source. Good thermometric properties such as absolute sensitivity up to 0.053 K⁻¹ and relative sensitivity up to 0.014 K⁻¹ with temperature resolution of ∼0.37 K have been attained with the Stark sublevels of the thermally coupled transitions (i.e., ²H_11/2, ⁴S_3/2 → ⁴I_15/2 level) of Er³⁺ ions. The reliability test of the temperature sensing ability and excellent thermal stability further confirm that the prepared phosphor can act as a worthy temperature probe.