Ultrasensitive Temperature Sensing Based on Ligand-Free Alloyed CsPbClx Br3- x Perovskite Nanocrystals Confined in Hollow Mesoporous Silica with High Density of Halide Vacancies.

Temperature sensing based on fluorescent semiconductor nanocrystals has recently received immense attention. Enhancing the trap-facilitated thermal quenching of the fluorescence should be an effective approach to achieve high sensitivity for temperature sensing. Compared with conventional semiconductor nanocrystals, the defect-tolerant feature of lead halide perovskite nanocrystals (LHP NCs) endows them with high density of defects. Here, hollow mesoporous silica (h-SiO2 ) template-assisted ligand-free synthesis and halogen manipulation (chloride-importing) are proposed to fabricate highly defective yet fluorescent CsPbCl1.2 Br1.8 NCs confined in h-SiO2 (CsPbCl1.2 Br1.8 NCs@h-SiO2 ) for ultrasensitive temperature sensing. The trap barrier heights, exciton-phonon scattering, and trap state filling process in the CsPbCl1.2 Br1.8 NCs@h-SiO2 and CsPbBr3 NCs@h-SiO2 are studied to illustrate the higher temperature sensitivity of CsPbCl1.2 Br1.8 NCs@h-SiO2 at physiological temperature range. By integrating the thermal-sensitive CsPbCl1.2 Br1.8 NCs@h-SiO2 and thermal-insensitive K2 SiF6 :Mn4+ phosphor into the flexible ethylene-vinyl acetate polymer matrix, ratiometric temperature sensing from 30.0 °C to 45.0 °C is demonstrated with a relative temperature sensitivity up to 13.44% °C-1 at 37.0 °C. The composite film shows high potential as a thermometer for monitoring the body temperature. This work demonstrates the unparalleled temperature sensing performance of LHP NCs and provides new inspiration on switching the defects into advantages in sensing applications.