Fast Room-Temperature Synthesis of K 3 ZrF 7 :Yb 3+ /Ho 3+ Nanocrystals for Highly Sensitive Nanothermometry

The emerge of thermoresponsive upconversion emissions opens up new possibilities for temperature sensing. However, it has remained a challenge to achieve anti-thermal quenching luminescence from fast-synthesized nanocrystals for thermometry. Here, we report a strategy to realize highly thermosensitive upconversion luminescence from K3ZrF7:Yb3+/Ho3+ nanocrystals that were rapidly synthesized in 1 min at room temperature, remarkably faster and simpler than the conventional synthetic methods. Interestingly, the upconverted emissions of Ho3+ show an efficient enhancement with an increasing temperature instead of thermal quenching, as shown in conventional phosphors. We demonstrated that the removal of the water molecules adsorbed at the surface plays a key role in enhancing Ho3+ upconversion by suppressing the non-radiative relaxation channels from its 5I6 level in the thermal field. When we take advantage of the luminescence intensity ratio of non-thermally coupled green and red emissions, a maximum relative sensitivity of 2.53% K–1 was achieved, which ranks in the high values for Ho3+-based thermometers. Our results provide a fast-synthesis and low-cost platform for highly sensitive non-contact nanothermometry toward cutting-edge applications.