Abstract
A promising technique based on the luminescence with long wavelength excitation and short wavelength emission (LExL, λ(ex-L) > λ(em)) is developed. This LExL is different from traditional upconversion luminescence (UCL). The LExL, namely, special "UCL", is realized by a xenon light source of a common spectrofluorometer. In this work, we found that dopamine (DA) has this LExL phenomenon. The LExL of DA is mainly caused by the excitations of second-order diffraction light (λ(ex-L)/2). The two-photon absorption properties of DA have been calculated employing the density functional response theory. The LExL and Stokes luminescence (SL, λ(ex-S) < λ(em)) of DA both showed static quenching upon the addition of Fe(3+). Dual-mode luminescence methods upon LExL (λ(ex-L)/λ(em) at 565/317 nm) and SL (λ(ex-S)/λ(em) at 282/317 nm) of DA were applied for the selective determination of Fe(3+). The detection limits are 0.30 and 0.52 μmol L(-1) for LExL and SL, respectively. In addition, their linear ranges for Fe(3+) determination are both from 0.70 to 30 μmol L(-1). The LExL method of DA not only meets the basic determination criteria for Fe(3+) but also offers additional advantages in resisting more interferences and shows satisfactory feasibility performances.