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_11/2/⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_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 × 10⁻³ K⁻¹ at 480 K. By utilizing a much safer excitation laser of 1550 nm, the maximum S_A achieves 8.4 × 10⁻³ K⁻¹ at 450 K, with a high and stable S_A of more than 7.9 × 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.