Optical thermometry using efficient upconversion luminescence in Er3+ self-sensitized NaYS2 under multi-wavelength excitation

Herein, a series of Er 3+ self-sensitized NaYS 2 phosphors are synthesized by the solid-gas reaction method for a novel upconversion luminescence thermometer. Er 3+ possesses abundant excited state energy levels in the near-infrared region, enabling efficient upconversion luminescence by absorbing different near-infrared wavelength light. Compared to 980 nm excitation, the emission intensity is enhanced by nearly an order of magnitude under 1532 nm excitation, which can be attributed to the larger absorption cross-section of 4 I 13/2 and stronger absorption efficiency for Er 3+ . Based on the luminescence intensity ratio technique, the optical thermometry behaviors of NaYS 2 :Er 3+ under different wavelength excitation are evaluated by employing the thermally coupled energy levels of 2 H 11/2 / 4 S 3/2 . It can be deduced that the excitation wavelength has no significant effect on the temperature sensing parameters. Compared to other typical upconversion luminescence thermometers, NaYS 2 :Er 3+ thermometer exhibits not only excellent sensitivity performance but also high upconversion luminescence efficiency, which is expected to be applied in wide-temperature-range and highly-sensitive temperature sensing. • Upconversion properties and mechanisms of Er 3+ self-sensitized NaYS 2 under 980/1532 nm excitation were analyzed. • LIR technique based on 2 H 11/2 / 4 S 3/2 of NaYS 2 :Er 3+ was used for temperature sensing. • Wide-range and highly-sensitive optical temperature sensing was realized. • No significant effect of excitation wavelength on thermometry parameters of Er 3+ was inferred by analyzing the performance.