Theoretical study of a water sensor based on a single upconversion microrod

Abstract

Water sensing is of great importance in wide applications of biomedicine, precision agriculture, chemical industrial processes, and food inspection. As a promising probe to detect water molecules, lanthanide-doped upconversion nanoparticles have drawn rapidly increasing research interest with the merits of the high photostability, fast response, and highly distinguishable spectrum. However, the detection sensitivity of such a technique is usually moderate due to the weak response of the luminescence to variations of water concentrations. Here, we theoretically study a sensitive water sensor based on a single NaGdF4:Yb3+/Tm3+ upconversion microrod. By utilizing whispering-gallery-mode resonance around the cross-section of the microrod, an upconversion laser is generated which can be employed to improve the detection sensitivity by about an order of magnitude compared with the sensors based on upconversion nanoparticle luminescence. The sensor is expected to be used for achieving the high-stability, high-sensitivity, high-spatial-resolution, and real-time detection of water molecules.