A dual-emitting dye@MOF composite has been synthesized by incorporating a fluorescent dye eosin Y (EY) within a UiO-type zirconium-based metal−organic framework (Zr-MOF) through a synthetic encapsulation method. The Zr-MOF prevents the aggregation of EY molecules and keeps EY molecules stably included after synthesis. As expected, an energy transfer from Zr-MOF to EY molecules occurred because of the good overlap between the emission of Zr-MOF and the absorption of EY. As a result, the obtained EY@Zr-MOF composite features a weak blue emission at 446 nm and a strong yellow emission at 553 nm. By using the relative height of the two emission peaks replacing absolute peak height as detecting signals, EY@Zr-MOF composite acts as a self-calibrating luminescent sensor for selectively detecting Fe 3+ , Cr 2 O 7 2− , and 2-nitrophenol. Furthermore, the observed fluorescence responses of the composite toward analyte are highly stable and reversible after recycling experiments. To the best of our knowledge, this is the first example of a dye@MOF-implicated self-calibrating sensor for Fe 3+ , Cr 2 O 7 2− , and 2-nitrophenol detection.

Nanocrystalline CaWO 4 and Eu 3+ (Tb 3+)-doped CaWO 4 phosphor layers were coated on non-aggregated, monodisperse and spherical SiO 2 particles by the Pechini sol-gel method, resulting in the formation of SiO 2 @CaWO 4 , SiO 2 @CaWO 4 :Eu 3+ /Tb 3+ core-shell structured particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), time-resolved PL spectra and lifetimes were used to characterize the core-shell structured materials. Both XRD and FT-IR indicate that CaWO 4 layers have been successfully coated on the SiO 2 particles, which can be further verified by the FESEM and TEM images. The PL and CL demonstrate that the SiO 2 @CaWO 4 sample exhibits blue emission band with a maximum at 420 nm (lifetime = 12.8 µs) originated from the WO 2− 4 groups, while SiO 2 @CaWO 4 :Eu 3+ and SiO 2 @CaWO 4 :Tb 3+ show additional red emission dominated by 614 nm (Eu 3+ : 5 D 0-7 F 2 transition, lifetime = 1.04 ms) and green emission at 544 nm (Tb 3+ : 5 D 4-7 F 5 transition, lifetime = 1.38 ms), respectively. The PL excitation, emission and time-resolved spectra suggest that there exists an energy transfer from WO 2− 4 to Eu 3+ and Tb 3+ in SiO 2 @CaWO 4 :Eu 3+ and SiO 2 @CaWO 4 :Tb 3+ , respectively. The energy transfer from WO 2− 4 to Tb 3+ in SiO 2 @CaWO 4 :Tb 3+ is more efficient than that from WO 2− 4 to Eu 3+ in SiO 2 @CaWO 4 :Eu 3+ .

A series of eosin Y (EY)-embedded zirconium-based metal−organic frameworks (Zr-MOFs) were prepared by utilizing the synthetic encapsulating method. By virtue of effective resonant energy transfer between Zr-MOF and EY, not only does EY@Zr-MOF exhibit dual-emissive characteristics, but also the relative intensity of their double emission is greatly tuned with increasing EY loading quantity. As a consequence, the double emission of EY@Zr-MOF presented large distinctions in location and intensity. By using the relative fluorescence intensity instead of the absolute fluorescence intensity of emission peaks as detection signals, two EY@Zr-MOFs served as built-in self-calibrated fluorescence sensors to detect pesticides, where EY@Zr-MOF realized the selective detection of nitenpyram, a kind of nicotine pesticide. These results indicate that the integration of robust Zr-MOF and fluorescence molecules provides a new research platform for pesticide sensing and recognition.

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