Improved relative temperature sensitivity of over 10% K^-1 in fluoride nanocrystals via engineering the interfacial...

Real-time in situ temperature sensing is of significance in the bio-medical field; however, the low relative temperature sensitivity S_r is one of the major obstacles in the development of nanothermometers. Herein, we provide an effective route that engineers the interfacial layer in a core/shell/shell nanostructure to enlarge the temperature-dependent luminescence intensity ratio (LIR) variations followed by an improved S_r. The CaF₂ interlayer is employed to inhibit the interaction between the core and outer shell, and increase the interfacial phonon energy to enhance the negative thermal quenching effect (TQE) of Nd³⁺ ions in the outer shell and positive TQE of Er³⁺ ions in the core layer. Based on the temperature-dependent LIR variations of Er (650 nm) to Nd (800 nm), the maximum S_r of 10.01% K^-1 and minimum S_r of % 2.56% K^-1 are achieved.