SrY₂S₄ - a novel host lattice for up-conversion luminescence and high-sensitive optical thermometry

Lanthanide ion-doped up-conversion (UC) luminescent materials are highly coveted for their utility in diverse applications such as anti-counterfeiting, fluorescence labeling, and temperature sensing. Here, we attempt to adopt SrY2S4 as a novel host lattice for UC luminescence and high-sensitive optical thermometry under near-infrared irradiation. The results show that the single Er3+-doped SrY2S4 samples present their main emissions in green and red regions under 1550 and 980 nm excitations, which correspond to the H-11/2/S-4(3/2) -> I-4(15/2) and F-4(9/2) -> I-4(15/2) transitions of Er3+ ions, respectively. The green to red intensity ratio increases with the Er3+ concentration under both 980 and 1550 nm excitations. The mechanisms of UC luminescence and energy transfer are further systematically investigated by UC spectra and fluorescence decay dynamics. Furthermore, the non-contact temperature sensing performance of the SrY2S4:10%Er3+ sample is explored via employing fluorescence intensity ratio (FIR) technology. At an excitation of 980 nm, the maximum absolute sensitivity (S-A) reaches 7.5 x 10(-3) K-1 at 480 K. By utilizing a much safer excitation laser of 1550 nm, the maximum S-A achieves 8.4 x 10(-3) K-1 at 450 K, with a high and stable S-A of more than 7.9 x 10(-3) K-1 over a broad temperature range of 360-570 K. The relative sensitivity is 1.06% and 1.01% K-1 under 980 and 1550 nm excitations, respectively. These results indicate that the ternary sulfide SrY2S4 can be adopted as a novel host to achieve promising UC luminescence and thermal sensing performance.