A ratiometric optical thermometer with dual-color emission based on Eu2+-doped CsCu2I3 microcrystals

With the increasing demand for non-contact fluorescence intensity ratio-based optical thermometry, novel phosphor materials with high-efficiency, dual-emitting centers, and differentiable temperature sensitivity are highly desired. In this work, rare earth Eu²⁺ ions were incorporated into CsCu₂I₃ microcrystals by solid-state reaction. Under a single UV excitation, the as-synthesized samples exhibit two emissions: 452 nm blue emission from the 5d→4f transition of Eu²⁺ and 582 nm yellow emission from self-trapped exciton emission of CsCu₂I₃. The photoluminescence quantum yield reaches to 50%. The dual-band emission of Eu²⁺-doped CsCu₂I₃ shows different temperature responses in the range of 260–360 K. Based on fluorescence intensity ratio technology, the maximum absolute sensitivity and relative sensitivity are 0.091 K^–1 (at 360 K) and 2.60%/K (at 260 K), respectively. These results suggest that Eu²⁺-doped CsCu₂I₃ could be a good candidate for highly sensitive optical thermometer.