Sensitive determination of chromium (VI) based on the inner filter effect of upconversion luminescent nanoparticles (NaYF4:Yb3+, Er3+)

A new method was developed for selective and sensitive determination of trace chromium (VI) based on the inner filter effect (IFE) of upconversion luminescent nanoparticles (NaYF4:Yb3+, Er3+) as fluorescence probes. In this study, water-soluble and well dispersible upconversion luminescent nanoparticles (NaYF4:Yb3+, Er3+) were firstly synthesized by hydrothermal method, and characterized by transmission electron microscopy (TEM) and luminescence spectroscopy. And then, the IFE method was established for determination of chromium (VI). The principle of this assay is based on the complementary overlap of the green emission band of nanoparticles (NaYF4:Yb3+, Er3+) with the absorption spectrum of a pink chelate complex (Cr(III)-diphenylcarbazone), which was generated by the quantitative reaction between diphenylcarbazide (DPC) and Cr(VI) in mineral acid solution. Under the optimal condition, the decrease in the upconversion luminescent nanoparticles was proportional to the concentration of chromium (VI) due to IFE. The linear range is 0.070–10.0×10−6 mol L−1 Cr(VI), and the limit of detection (3σ) is 2.40×10−8 mol L−1 Cr(VI). The method described here is sensitive than the method of spectrophotometry. This assay was used in the determination of Cr(VI) in water samples.