Facile synthesis of Er3+/Yb3+-codoped NaYF4 nanoparticles: a promising multifunctional upconverting luminescent material for versatile applications

The Er3+/Yb3+-codoped NaYF4 upconverting nanoparticles were prepared by a facile hydrothermal method. Under the excitation of 980 nm, the obtained compounds exhibited the featured emissions of Er3+ ions. The optical thermometric performance of the Er3+/Yb3+-codoped NaYF4 nanoparticles based on the thermally coupled H-2(11/2) and S-4(3/2) levels of Er3+ ions in the temperature range of 93-673 K was investigated by the fluorescence intensity ratio technique. The maximum sensitivity was approximately 0.0029 K-1, indicating that both low-and high-temperature detection can be synchronously achieved in Er3+/Yb3+-codoped NaYF4 upconverting nanoparticles. Furthermore, the temperature-dependent emitting color was discussed and it was changed from yellow to red with raising the temperature from 93 to 673 K. In addition, the internal heating properties of the developed nanoparticles caused by laser excitation power were also analyzed. It is found that the temperature of nanoparticles was elevated from 255.03 to 372.03 K with the increment of pump power from 84 to 585 mW. These characteristics suggest that the Er3+/Yb3+-codoped NaYF4 upconverting nanoparticles are a promising candidate for optical temperature sensors and safety signs as well as optical heaters.