Upconversion luminescence and temperature sensing performance of Er3+ ions doped self-activated KYb(MoO4)2 phosphors

Abstract

In this work, a series of self-activated KYb(MoO₄)₂ phosphors with various x at% Er³⁺ doping concentrations (x = 0.5, 1, 3, 5, 8, 10, 15) was synthesized by the solid-state reaction method. The phase structure of the as-prepared samples was analyzed by X-ray diffraction (XRD), XRD Rietveld refinement and Fourier transform infrared (FT-IR) spectroscopy. The as-prepared samples retain the orthorhombic structure with space group of Pbcn even Er³⁺ doping concentration up to 15 at%. High-purity upconversion (UC) green emission with green to red intensity ratio of 55 is observed from the as-prepared samples upon the excitation of 980 nm semiconductor laser and the optimum doping concentration of Er³⁺ ions in the self-activated KYb(MoO₄)₂ host is revealed as 3 at%. The strong green UC emission is confirmed as a two-photon process based on the power-dependent UC spectra. In addition, the fluorescence intensity ratios (FIRs) of the two thermally-coupled energy levels, namely ²H_11/2 and ⁴S_3/2, of Er³⁺ ions were investigated in the temperature region 300–570 K to evaluate the optical temperature sensor behavior of the sample. The maximum relative sensitivity (S_R) is determined to be 0.0069 K⁻¹ at 300 K and the absolute sensitivity (S_A) is determined to be 0.0126 K⁻¹ at 300 K. The S_A of self-activated KYb(MoO₄)₂:Er³⁺ is almost twice that of traditional KY(MoO₄)₂:Er³⁺/Yb³⁺ codoping phosphor. The results demonstrate that Er³⁺ ions doped self-activated KYb(MoO₄)₂ phosphor has promising application in visible display, trademark security and optical temperature sensors.