Preparation of core–shell structured NaYF4:Yb3+/Tm3+@NaYF4:Yb3+/Er3+ nanoparticles with high sensitivity, low resolution and good reliability and application of their fluorescence temperature properties

Abstract

A series of NaYF₄:Yb³⁺/Tm³⁺@NaYF₄:Yb³⁺/Er³⁺ nanoparticles doped with Tm³⁺ and Er³⁺ were successfully prepared by the solvothermal method. Under 980 nm laser excitation, intense upconversion emission peaks of Tm³⁺ and Er³⁺ were observed for all samples. By doping Tm³⁺ and Er³⁺ with core–shell partitioning, not only a significant increase in fluorescence intensity could be achieved, but also simultaneous temperature measurements on multiple thermocouple energy levels could be realised. In addition, the temperature sensing performance of different thermocouple energy levels was also investigated, and it was found that the ³F₃ → ³H₆ and ¹G₄ → ³F₄ thermocouple energy level pairs of Tm³⁺ were the best, with maximum absolute sensitivity and maximum relative sensitivity of up to 0.0250 K⁻¹ and 2.155% K⁻¹ respectively, higher than the sensitivity of other thermocouple energy levels. It has a temperature resolution of less than 0.0139 K, which is lower than that of most materials available today. By using this material as a probe to build a fiber optic temperature sensor platform, it was found to have reliable temperature measurement performance.