An “Off–On” Hg(II) sensor excited by near-infrared to visible upconversion nanorods

In this work, we constructed a Hg(II) sensor using β-NaYF4:Yb3+/Er3+ nanorods as the excitation source and a rhodamine derivative as the probe. The sensing system was fully characterized and discussed by electron microscopy, XRD analysis, IR spectra and thermogravimetric analysis. The energy transfer process between the excitation source and the probe was also investigated by excitation/emission spectra and excited state lifetime analysis. The result suggested that the upconversion emission from the excitation source could effectively excite the probe. Then the sensing behavior towards Hg(II) was evaluated by emission spectra and the Stern–Volmer plot. It was found that the emission of the sensing system increased with the increasing Hg(II) concentration, showing an “off–on” effect towards the analyte. In addition, the sensing system owned a high selectivity towards the analyte, making itself a promising sensing system towards Hg(II).