Luminescence lifetime thermometers based on hybrid cuprous halides with exceptional water resistance and giant thermal expansion

Optical probes hold great promise for temperature sensing owing to their attractive properties including rapid response, high spatial resolution, and remote non-invasive detection. However, the exploration of thermometric probes is hindered by their low relative sensitivity (S_r) or poor structural stability in water. Herein, we propose the first example of organic-inorganic metal halides based on TPP₃Cu₂Br₂ (TPP = triphenylphosphine) that simultaneously present excellent water resistance and sensitive temperature-dependent photoluminescence lifetime in water. Benefiting from the soft lattice induced by the organic molecule of TPP, giant thermal expansion and great lattice distortion were achieved with increasing temperature. As such, the self-trapped exciton luminescence lifetime of TPP₃Cu₂Br₂ can be shortened to 1.9% of the initial value from 280 to 380 K, resulting in the highest S_r of 12.82% K^-1 among the undoped metal halides based luminescent thermometers. Significantly, TPP₃Cu₂Br₂ displayed extraordinary water stability with emission intensity remaining nearly unchanged after immersing in water for 15 days. Moreover, high-precision luminescence lifetime based thermal sensing in water environment was successfully conducted, which proved to be inert to the detection depth in water with a small read-out error. This work offers new routes in the exploration of novel metal halides for highly sensitive thermometric probes toward versatile application scenarios.