Highly luminescent GdVO 4 :Eu 3+ /carbon dots (CDs) nanocomposite was synthesized by hydrothermal deposition method for the first time. With the use of dialyzed CDs solution as precursor, the synthetized composite shows negligible emission intensity of CDs. On replacing the dialyzed CDs solution with the crude one, highly luminescent composite can be obtained successfully. Based on the analysis of XPS and FT-IR spectra, one can deduce that the existence of a large amount of citrate anions, ethylenediamine cations and polymer-like CDs in the crude CDs solution make it as nutrient solution of CDs, which can not only facilitate growth of CDs on the surface of GVE, but also greatly prevent nitrogen atoms from falling off the particles during the hydrothermal deposition process. For the dialyzed CDs solution, due to the ions and polymer-like CDs being thoroughly dialyzed, the coated CDs are fragile during hydrothermal deposition process. Besides, the effects of different dosages of ammonia on emission intensities of the two composites are studied. Based on the designable patterns for security application, one can think that the highly luminescent composite is one of the most promising candidates in the anti-counterfeiting field.
To obtain optimal luminescence, 0.12 g of GdVO 4 :3%Eu 3+ nanocrystals (NCs) and different volumes of nitrogen-doped carbon dots (N-CDs) crude solution were used as precursors, and the composite synthesized using the hydrothermal deposition method showed optimal luminescence when 11 ml (2.45 mmol) crude solution was used. In addition, similar composites with the same molar ratio as GVE/cCDs(11) were also prepared with the hydrothermal and physical mixing processes. Based on the test results of XRD, XPS, and PL spectra, for the composite GVE/cCDs(11), the highest (lowest) peak intensity of the C–C/C=C (C=O/C=N) bond, which was 1.18 (0.75) times that of GVE/cCDs-m, indicated most N-CDs deposition and led to their highest emission intensity under 365 nm excitation, although nitrogen atoms in the composite were shed slightly during the deposition process. Finally, as can be seen from the patterns designed for security applications that the optimally luminescent composite is one of the most promising candidates in the anti-counterfeiting field.
GdVO 4 :Eu 3+ nanophosphors were prepared via molten salt synthesis. Equal moles of NaNO 3 and KNO 3 were used as reaction medium, rare earth nitrates and NH 4 VO 3 as precursors, and NaOH as alkalizer. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), photoluminescence (PL) spectrum and lifetime were used to characterize the nanophosphors. XRD demonstrates that NaOH concentration and the sintering temperature play important roles in the crystallinity and the phase purity of the products. The optimum NaOH concentration and sintering temperature are 2:40 and 400 °C, respectively. TEM micrographs show that the GdVO 4 :Eu 3+ nanocrystals exhibit a cubic morphology and have a mean size of about 20 nm, which is in good agreement with that calculated by Scherrer's formula. Both the cell parameters and the volume of GdVO 4 :Eu 3+ nanocrystals decrease due to the existence of big quantity of dangling bonds on the particle surface. Upon excitation at 315 nm, the GdVO 4 :Eu 3+ nanocrystals show the strong characteristic emission of Eu 3+ , which indicates the efficient energy transfer from VO 4 3- groups to Eu 3+ . The best doping concentration of Eu 3+ in GdVO 4 is determined to be 5 mol%.
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