An "off–on" fluorescence probe for Hg(II) detection using upconversion nanobars as the excitation source: Preparation, characterization and sensing performance

In this paper, we reported an "off–on" optical sensor for Hg(II) detection using upconversion β-NaYF4:Yb3+/Er3+ nanobars as the excitation source and a rhodamine derivative as the probe. The nanocomposite was characterized and studied by electron microscopy, XRD analysis, IR spectra, thermogravimetry and photophysical measurements. The energy transfer mechanism between the upconversion excitation source and the rhodamine based probe was analyzed by their emission/excitation spectra and excited state lifetime comparison. Experimental results suggested that the upconversion emission form the excitation source could effectively excite the probe. The sensing performance of the nanocomposite towards Hg(II) was also studied. It was found that the emission intensity of the nanocomposite increased with the increasing Hg(II) concentration, showing an "off–on" phenomenon. In addition, the emission signal of the nanocomposite was immune to other metal ions, providing a high selectivity towards Hg(II). -- Highlights: • An "off–on" optical sensor for Hg(II) detection was constructed. • Upconversion β-NaYF4:Yb3+/Er3+ was used as the excitation source. • A rhodamine derivative was connected to β-NaYF4:Yb3+/Er3+ as the probe. • The nanocomposite and its sensing performance were fully studied