The advancement of non-contact temperature measurement has brought about significant interest due to its rapid response, broad applicability, and minimal thermal inertia. However, challenges such as spectral peak position modulation, sensitivity improvement, and reliable performance enhancement continue to persist in this field. In this study, a double halide perovskite single-crystal Cs2InCl5∙H2O was synthesized, with the introduction of Bi3+ ions modulating the photoluminescence from orange to blue. Meanwhile, the deep-blue emission peaked at 410 nm, boasting a high photoluminescence quantum yield (PLQY) of nearly 46 % under 340 nm excitation. Furthermore, by incorporating varying concentrations of Bi3+ ions, two distinct emission peaks were generated, facilitating effective signal differentiation for temperature detection. Utilizing the thermal quenching responses of these two emission peaks, a temperature-detection methodology based on the fluorescence intensity ratio (FIR) was developed, using donor-acceptor pair emission as detection signals and self-trapped emission as reference signals. The designed Cs2InCl5∙H2O:0.07Bi3+ exhibits a maximum Sa of 0.082 K-1 and Sr of 3.349 %K−1, respectively. The spectral adjustability and high sensitivity achieved through cation-substitution strategy in this study offer a promising pathway for the development of advanced optical thermometry materials with enhanced performance characteristics.