Preparation And Photoluminescence Of Eu³⁺ Or Dy³⁺ Ions Doped Zn Wo₄ Luminescent Materials

As a type of excellent matrix materials, tungstates have some merits, e.g., high chemical stability, high light yield, high X-ray absorption coefficient, and non-toxicity. In this paper, a series of Eu3+ or Dy3+ ions doped Zn WO4 luminescent materials have been synthesized by hydrothermal method or hydrothermal route followed by calcining process. The phase structure, morphology and luminescent properties of as-synthesized samples were characterized by X-ray diffraction, fourier transform infrared spectroscope, scanning electron microscope, and fluorescence spectrophotometer, respectively. The main research contents and results are as follows:(1) A series of Zn WO4:Eu3+ nano-sized phosphors were synthesized by hydrothermal method at different conditions. All of the obtained samples are pure monoclinic wolframite structure. The Zn WO4:Eu3+ samples are composed of spherical nanoparticles, and the particle size of samples increases a little with increasing the hydrothermal temperature and time. The excitation spectrum of Zn WO4:Eu3+ shows a broad band extending from 220 to 350 nm and a series of sharp peaks in the range of 350 to 500 nm, and the strongest peak located at 301 nm. The broad excitation band is ascribed to the charge transfer transition of W-O and Eu-O. The sharp excitation peaks are attributed to the f-f transition of Eu3+. The emission spectrum of the sample Zn WO4:Eu3+ under the excitation at 301 nm is composed of the weak broad band attributing to the intrinsic emission of WO42- and a series of sharp emission peaks originating from the characteristic emission of Eu3+. The emission intensity of Eu3+ at 616 nm reaches the strongest when the p H value of the reaction system is 6, the hydrothermal temperature is 180 ℃, the hydrothermal time is 12 h, and the Eu3+ concentration is 2 mol.% under the excitation at 301 nm. Meanwhile, it is found that the emission intensity of Eu3+ reaches the highest when Eu3+ concentration is 6 mol.% under the excitation at 395 nm and 465 nm. Moreover, the photoluminescence color of the Zn WO4:Eu3+ phosphors can be tuned from blue, white, and orange to red by increasing the doping concentrations of Eu3+.(2) Zn WO4:Eu3+ nanorods were synthesized by hydrothermal method using ethylene glycol(EG), glycerol(Gly), polyethylene glycol-10000(PEG-10000) and sodium dodecyl sulfonate(SDS) as surfactant respectively. The obtained samples are pure wolframite structure. The particles of the as-synthesized samples under the different surfactants are basically short rods in shape, but the slenderness ratios are different. The rodlike particles of the sample using Gly as the surfactant are smaller in slenderness ratio and are homogeneous in size. While using EG, PEG-10000 and SDS as the surfactants, the particles are larger in slenderness ratio and are inhomogeneous in size. The main emission peak of Zn WO4:Eu3+ nanorods is at 616 nm, which is ascribed to 5D0â†'7F2 electronic dipole transition of Eu3+. The different surfactants have great effect on the intensity of excitation peak and emission peak of the samples, and the intensity order is IPEG-10000>ISDS>IEG>IGly.(3) The single-phased white light-emitting phosphors Zn WO4:Eu3+ were synthesized by hydrothermal route followed by calcining process. All of the obtained samples are pure monoclinic wolframite structure. The Zn WO4:Eu3+ samples are composed of spherical particles. After calcining, the crystallinity, particle size and luminescent intensity of the samples significantly increase. The emission intensity of Eu3+ first increases, and then decreases with the increase of Eu3+ concentration. When the Eu3+ concentration is 2 mol.%, the emission intensity of Eu3+ reaches the maximum. Moreover, all of the color coordinates of Zn1-x WO4:Eu3+x(x=0.5, 2, 4, 6 mol.%) phosphors are situated in the white light zone in the CIE chromaticity diagram, and the color coordinate of Zn1-x WO4:Eu3+x(x=2 mol.%) phosphor is very close to the standard white chromaticity.(4) A new white luminescent material Dy3+ doped Zn WO4 was synthesized by hydrothermal route followed by calcining process. The sample is pure Zn WO4:Dy3+ only when the p H value of the reaction system is 6. The Zn WO4:Dy3+ sample is composed of spherical particles, and the particle size is about 80-130 nm. The excitation spectrum of Zn WO4:Dy3+ consists of a broad band ascribed to the charge transfer transition from oxygen ligand to tungsten ion. The emission spectrum of Zn WO4:Dy3+ is composed of two major parts: the broad band attributing to the intrinsic emission of WO42- and the 4F9/2â†'6H15/2 magnetic dipole transition of Dy3+, and the sharp emission peak corresponding to the 4F9/2â†'6H13/2 electric dipole transition of Dy3+. The optimal emission intensity of the Zn1-x WO4:Dy3+x phosphors is realized when x=1.5 mol.%. Moreover, all of the Zn1-x WO4:Dy3+x(x=0.5, 1, 1.5, 2 mol.%) phosphors can exhibit white light emission, which can be potentially applied in white lighting-emitting diodes.