The synthesis of Er3+/Yb3+/K+ triple-doped NaYF4 phosphors and its high sensitivity optical thermometers at low power

Optical Thermometry is popular among researchers because of its non-contact, high sensitivity, and fast measurement properties. In the present experiment, Er 3+ /Yb 3+ /K + co-doped NaYF 4 nanoparticles with different K + concentrations were synthesized by solvothermal method , and the samples showed bright upconversion green emission under the excitation of a 980 nm laser. The powder X-ray diffractometer and transmission electron microscope were used to characterize the crystal structure and its surface morphology , respectively. The spectral characteristics of nanoparticles with K + doping concentration from 10% to 30% (Molar ratio) were investigated by fluorescence spectroscopy , and it was observed that the fluorescence intensity reached the maximum at the K + concentration of 20%, after which the intensity weakened when the K + content continued to increase. According to the dependence between the luminescence intensity of the sample and the laser power density and fluorescence lifetime , the intrinsic mechanism was carefully investigated. Temperature-dependent spectra of the samples were recorded in the temperature range of 315–495 K， and the maximum values of absolute sensitivity (S a ) and relative sensitivity (S r ) were measured at 0.0041 K −1 (455 K) and 0.9220%K −1 (315 K). The experimental results show that K + /Er 3+ /Yb 3+ triple-doped NaYF 4 green fluorescent nanoparticles (GFNs) have good prospects for applications in display devices, temperature sensing, and other fields.