Nearly monodisperse,regular-shaped and well oil-dispersible tetragonal BaYF5:0.2Yb3+/0.02Er3+ nanocrystals(NCs) were synthesized in water-ethanol-oleic acid-sodium oleate system.The as-obtained NCs exhibited bright upconversion(UC) fluorescence under the 980 nm excitation.Blue(2H9/2-4I15/2),green((2H11/2,4S3/2)-4I15/2) and red(4F9/2-4I15/2) transitions were observed.The results indicated that the relative intensity of green to red increased gradually with increasing power density,which were seldom in the previous work.Therefore,the UC properties and mechanism were studied in detail.
A facile preparation of nitrogen-doped β-TiO2（N-doped β-TiO2） nanobelts and their visible-light photocatalytic activity were reported.The preparation of N-doped β-TiO2 nanobelts consisted of cation-exchange between layered sodium titanate nanobelts and NH 4 ＋ in aqueous solution at room temperature and subsequent calcination in air.Such a calcination treatment is beneficial to the formation of monoclinic N-doped β-TiO2 nanobelts.Various measurement results indicate that not only were the nitrogen atoms doped into the lattice of β-TiO2 nanobelts resulting in a strong visible-light absorption,but also a large number of defects were caused by them in the lattice,increasing the stability of β-TiO2.The photocatalysis enhancement of N-doped β-TiO2 nanobelts for the photodegradation of Rhodamine B was demonstrated.
A series of new red-emitting BaCa1–2xBO3F：xEu3＋, xM＋ （M=Li, Na, K） phosphors were synthesized by the solid-reaction method. X-ray diffraction （XRD）, diffuse reflection （UV-vis） and photoluminescence spectra were utilized to characterize the crystallization process, structure and luminescence properties of the as-synthesized phosphors. The XRD results indicated that the sample began to crystallize at 800 oC, and single-phase BaCaBO3F was fully obtained after annealing at 1000 oC. The charge compensated behaviors were investigated in this paper by considering different cations like Li＋, Na＋ and K＋ acting as the charge compensator. The as-prepared phosphors had better emission properties, and the two characteristic emission lines peaking at 590 and 615 nm could be obtained upon 394, 463 and 532 nm excitation with the chromaticity coordinates of （0.596, 0.391）, which were due to 5D0–7F1 and 5D0–7F2 transitions of Eu3＋ ions. Further, the concentration quenching and corresponding luminescence mechanisms of BaCa1–2xBO3F：xEu3＋, xNa＋ phosphors were also discussed.
Trivalent rare-earth ions （La3＋,Pr3＋,Nd3＋,Sm3＋,Gd3＋,Tb3＋,Dy3＋,Ho3＋,Er3＋,Tm3＋,and Yb3＋） were investigated as the codoped auxiliary sensitizer for the electron trapping materials SrS：Eu2＋ in order to enhance the fluorescence properties.It was found that Sm3＋ and Tb3＋ had the best photoluminescence stimulated luminescence （PSL） effect among the selected trivalent rare-earth ions.All the SrS：Eu2＋ samples doped by different trivalent rare-earth ions could be stimulated by 980 nm laser after being exposed to the conventional sunlight,and they emitted PSL with the peak located at 615 nm.The result also indicated that some co-doped rare earth ions could increase fluorescence intensities of the traditional electron trapping materials SrS：Eu2＋.
Micro- and nanocrystals cubic-phase SrF2：yb^3＋/Er^3＋ upconversion luminescence phosphors were synthesized via a facile hydro- thermal route in the presence of different surfactants. The samples were characterized with X-ray diffraction （XRD）, Fourier transtbrm infra- red spectra （FT-IR）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and upconversion emission spectra. As-prepared products showed a variety of morphologies, such as cubic-shaped microcrystal, hierarchical structure microspheres, spheri- cal-shaped nanocrystals and nanosheets. The intrinsic structural feature of cubic-phase SrF2 and two important external factors, namely, the surfactants in the reaction solution and fluoride sources, were responsible for shape determination of SrF2：yb^3＋/Er^3＋. The possible formation mechanisms for products with various architectures were presented. A systematic study on the photoluminescence of yb^3＋/Er^3＋-doped SrF2 samples with cubic shape, microspheres, spherical and nanosheets shapes showed that the optical properties of these products were strongly dependent on their morphologies and size.
Monoclinic Cu3V2O7（OH）2·2H2O（copper polyvanadate） hollow spheres were prepared with Na2V6O16·3H2O nanobelts as V-precursor by hydrothermal method. The purity and structure of the products were characterized by X-ray powder diffraction（XRD）, Fourier transform infrared（FTIR） spectroscopy, Raman spectroscopy, thermogravimetric analysis（TGA） and X-ray photoelecton spectroscopy（XPS）. The morphology and size were observed by scanning electron microscopy（SEM）. We found that the Kagomé staircase-structural copper polyvanadate hollow spheres with an average diameter of 7 μm could be easily synthesized via the reaction of Na2V6O16·3H2O nanobelts with sufficient copper sulfate. The dielectric property of the copper polyvanadate demonstrates that dielectric loss hardly changes when the frequency of applied electric field is higher than 100 kHz. The formation process of the hollow spheres is discussed in detail by the observation of a series of products prepared for different reaction time.
YANG FangJI Tian-haoDU Hai-yanSUN ha-yueYANG Qing-linGE Guang-lu
