Ultra-Sensitive water detection based on NaErF4@NaYF4 high-level-doping upconversion nanoparticles

Abstract Water-sensitive detection plays a vital role in our society and life, such as the chemical industry, environmental monitoring, and food inspection. In this work water sensitivity as high as 5 ppm (0.0005 vol%) is realized based on a novel upconversion nanophosphor. Different from the popularly employed low-doping strategies, an efficient high-level-doping nanostructure, i.e., NaErF4@NaYF4, is tailored for the desired upconversion emission, resulting in more than one order of magnitude enhancement of the sensitivity compared to the record of the doped counterparts. The superiority of this structure is determined to come from the robust interactions between the Er3+ ions and the water molecules adsorbed on the particle surface. This design offers a new strategy of nanophosphor structures for ultrasensitive water sensing and sheds light on further optimization of nanophosphor based sensors.