Anomalous temperature dependence of photoluminescence lifetime in CsPbBr3 quantum dot-polymer film for optical thermometry

Here, we report the temperature dependence of the photoluminescence (PL) lifetimes of didodecyl dimethylammonium bromide (DDAB)/tetraoctylammonium bromide (TOAB) capped CsPbBr3 QD-based films and the elucidation of their potential application to optical thermometry. Compared to the unstable oleic acid (OA)/oleylamine (OAm) capped CsPbBr3 QD film, DDAB/TOAB-CsPbBr3 QD film exhibits a reproducible temperature-dependent characteristic of PL lifetimes in the temperature range of 15–80 °C. The anomalous temperature-dependent feature of PL lifetimes, i.e., positively correlated with temperature, is observed from DDAB/TOAB-CsPbBr3 QD and DDAB/TOAB-CsPbBr3 QD-polymer films. The prolonged PL lifetime at higher temperatures pertains to the dissociation of bound excitons to long-lived free excitons in CsPbBr3 QDs by overcoming the interaction with the trapping centers using the gained thermal energy. CsPbBr3 QD-polystyrene (PS) film exhibits superior relative sensitivity and temperature resolution for temperature sensing, demonstrating its suitability to be the material for fluorescent thermometry. The high dielectric constant of the PS medium facilitates bound excitons of CsPbBr3 QD to dissociate and further participate in the radiative recombination of free excitons, resulting in the improved thermometric properties of CsPbBr3 QD-PS film.