Optical temperature-sensing phosphors with high sensitivities in a wide temperature range based on different strategies

Abstract

Rare earth ion doped luminescent materials are considered potential candidates with a wide range of applications because of their unique optical characteristics. In this work, single-phase Yb³⁺–Er³⁺ and Yb³⁺–Tm³⁺ co-doped La_1.55SiO_4.33 (LS) phosphors of a hexagonal system for optical thermometers are reported. Three characteristic emissions of Er³⁺ were observed at 521, 553 and 659 nm in the LS:Yb³⁺,Er³⁺ phosphors under 980 nm excitation, which are assigned to the ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions, respectively. In the LS:Yb³⁺,Tm³⁺ phosphors, one can find two strong emissions at 474 and 790 nm and two weak emissions at 648 and 685 nm. Their upconversion (UC) luminescence mechanisms were studied from their pump-power-dependent spectra. When the samples were measured at various temperatures, their spectral features revealed that different fluorescence intensity ratio (FIR) strategies can be used to characterize their optical temperature-sensing behaviors. The sensor sensitivities were determined from the temperature-dependent UC emission spectra using thermally coupled energy levels (TCELs) and non-TCELs, which had improved compared with those of some other reported optical temperature-sensing luminescent materials. The device fabrication indicated that the developed UC phosphors are promising for applications in optical thermometers.