Yb and Re (Re = Er, Ho) codoped Sr2ScSbO6 double perovskites: dual-color upconversion luminescence for optical thermometry

Yb and Re (Re = Er, Ho) codoped Sr₂ScSbO₆ double perovskite phosphors were synthesized via high-temperature solid-state reaction. Under excitation by a 980 nm laser, the Yb 3 ⁺/Er 3 ⁺ codoped sample exhibits weak green emissions at 522 and 558 nm, along with a dominant red emission at 660 nm, which is attributed to efficient cross-relaxation processes that enhance population of the 4 F 9/2 level. Notably, the emission intensities are temperature-dependent, resulting in distinct and visible changes in emission color with increasing temperature. Temperature sensing based on the fluorescence intensity ratio (FIR) demonstrates a maximum relative sensitivity of 0.73% K⁻ 1 at 490 K and an absolute sensitivity of 1.43% K⁻ 1 at 730 K. In contrast, the Yb 3 ⁺/Ho 3 ⁺ codoped sample exhibits dual green (543 nm) and red (661 nm) emissions, along with superior performance in high temperatures, achieving a relative sensitivity of 0.59%·K⁻ 1 and an absolute sensitivity of 0.42%·K⁻ 1 at 670 K. These results suggest that the Yb 3 ⁺/Er 3 ⁺ system is more suitable for low-to-intermediate temperature sensing, while the Yb 3 ⁺/Ho 3 ⁺ system is better suited for high-temperature optical thermometry applications.