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

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 2H11/2 and 4S3/2, 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 (SR) is determined to be 0.0069 K−1 at 300 K and the absolute sensitivity (SA) is determined to be 0.0126 K−1 at 300 K. The SA 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.