Effect of excitation energy on non-thermally coupled temperature sensing of NaGdF4:Yb3+/Er3+ upconversion nanocrystals

Abstract

Many efforts have focused on ratiometric upconversion temperature sensing, but little attention has been paid to its measurement accuracy. Herein, the effect of excitation energy on temperature sensing is investigated comprehensively by using the hexagonal NaGdF4:Yb3+/Er3+ upconversion nanocrystals. It is demonstrated that the non-thermally coupled thermometer can reliably measure the temperature only when it operates in the suitable temperature range or under constant excitation conditions. By contrast, the classic thermal-coupled one does not suffer from these problems. Our research provides new insight into non-thermally coupled upconversion thermometers.