Nanostructured CaWO4, CaWO4 : Pb2+ and CaWO4 : Tb3+ particles: polyol-mediated synthesis and luminescent properties

Nano-submicrostructured CaWO4, CaWO4 : Pb2+ and CaWO4 : Tb3+ particles were prepared by polyol method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), thermogravimetry-differential thermal analysis (TG-DTA), photoluminescence (PL), cathodo-luminescence (CL) spectra and PL lifetimes. The results of XRD indicate that the as-prepared samples are well crystallized with the scheelite structure of CaWO4. The FE-SEM images illustrate that CaWO4 and CaWO4 : Pb2+ and CaWO4 : Tb3+ powders are composed of spherical particles with sizes around 260, 290, and 190 nm respectively, which are the aggregates of smaller nanoparticles around 10-20 nm. Under the UV light or electron beam excitation, the CaWO4 powders exhibits a blue emission band with a maximum at about 440 nm. When the CaWO4 particles are doped with Pb2+, the intensity of luminescence is enhanced to some extent and the luminescence band maximum is red shifted to 460 nm. Tb(3+)-doped CaWO4 particles show the characteristic emission of Tb3+ 5D4-7FJ (J = 6 - 3) transitions due to an energy transfer from WO4(2-) groups to Tb3+.     

Nanostructured CaWO4, CaWO4:Eu3+ and CaWO4:Tb3+ particles: sonochemical synthesis and luminescent properties

Nanostructured CaWO4, CaWO4:Eu3+, and CaWO4:Tb3+ phosphor particles were synthesized via a facile sonochemical route. X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, low voltage cathodoluminescence spectra, and photoluminescence lifetimes were used to characterize the as-obtained samples. The X-ray diffraction results indicate that the samples are well crystallized with the scheelite structure of CaWO4. The transmission electron microscopy and field emission scanning electron microscopy images illustrate that the powders consist of spherical particles with sizes from 120 to 160 nm, which are the aggregates of even smaller nanoparticles ranging from 10 to 20 nm. Under UV light or electron beam excitation, the CaWO4 powder exhibited a blue emission band with a maximum at 430 nm originating from the WO4/2- groups, while the CaWO4:Eu3+ powder showed red emission dominated by 613 nm ascribed to the 5D0 --> 7F2 of Eu3+, and the CaWO4:Tb3+ powders showed emission at 544 nm, ascribed to the 5D4 --> 7F5 transition of Tb3+. The PL excitation and emission spectra suggest that the energy is transferred from WO4/2- to Eu3+ CaWO4:Eu3+ and to Tb3+ in CaWO4:Tb3+. Moreover, the energy transfer from WO4/2- to Tb3+ in CaWO4:Tb3+ is more efficient than that from WO4/2- to EU3+ in CaWO4:Eu3+. This novel and efficient pathway could open new opportunities for further investigating the novel properties of tungstate materials.     

CaWO_4粉体和CaWO_4一维阵列的制备及光致发光特性

采用溶胶-凝胶法及辅助氧化铝模板法分别制备CaWO4粉体和CaWO4一维阵列,研究合成CaWO4粉体和一维陈列的光致发光特性。结果表明,制备的样品是纯CaWO4粉体;CaWO4粉体的强发光峰是位于410 nm的宽带谱,而CaWO4一维阵列的强发光峰在450 nm处,其光致发光曲线呈现宽化和强发光峰位的红移,这是样品和模板的光致发光光谱耦合的结果。     

Hydrothermal temperature dependence of CaWO4 nanoparticles: structural,optical, morphology and photocatalytic activity

Journal of Materials Science: Materials in Electronics - In this paper, CaWO4 nanoparticles were prepared by the hydrothermal method using the temperature of 100 (CaWO4-100), 120 (CaWO4-120), 140...     

Environmentally friendly aqueous solution synthesis of hierarchical CaWO4 microspheres at room temperature

An environmentally friendly route for the synthesis of hierarchical CaWO4 microspheres with novel morphology at room temperature has been successfully developed. CaCl2 and Na2WO4 were used as reaction regents, and distilled water was used as an environmentally friendly solvent. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence spectroscopy. This green wet-chemical route provides a simple, one-step, low-cost approach for the large-scale synthesis of hierarchical CaWO4 microspheres with relatively uniform diameters of 3-6 microm. The hierarchical microspheres are built up with numerous nanorods with an average diameter of 50 nm, which are radially oriented to the microsphere center. SEM observations of different intermediates indicate the possible growth process, in which the hierarchical structure growth is from nuclei through kayak-like, rod-like, peanut-like, dumbbell-like, and peach-like structures to final microspheres, via "self-assembled preferential end growth" of kayak-like particles in aqueous solution. The hierarchical CaWO4 microspheres exhibit a strong, broad blue emission peak of 412 nm.     

Microcontact printing and selective surface dewetting for large area electronic applications

A universal microstructuring approach was developed, which facilitates the patterning of surfaces by a combination of microcontact printing (mCP) and selective surface dewetting/wetting. Self-assembled monolayers (SAMs) were patterned on glass or silicon substrates by μCP. The regions coated by the SAMs turn hydrophobic, whereas the uncoated regions stay hydrophilic. Such functionalized surfaces facilitate selective deposition of polymers or resists. Polymethyl methacrylate and prepolymer polyurethane were selectively deposited on the hydrophilic regions of the substrate. The hydrophobic regions of the substrate stay uncoated. Subsequently, the resist was used to lift-off metallic microstructures in order to realize micro coils and electrodes for radio frequency information tags. The printed electrodes were used to define drain and source contacts of organic thin film transistors. The device characteristic of the organic transistors will be presented.     

Dy3+掺杂CaWO4荧光粉体的制备及发光性能

采用固相陶瓷方法制备了Dy3+掺杂的CaWO4∶Dyx3+荧光粉体。采用XRD、SEM和FT-IR对制备粉体的微观结构进行了表征;采用荧光分析法研究了制备的荧光体的室温光致发光性能;探讨了掺杂剂Dy3+浓度对CaWO4∶Dyx3+荧光粉体的微结构和光致发光性能的影响。结果表明,制备的CaWO4∶Dyx3+荧光粉体为白钨矿结构,Dy3+的掺入会抑制CaWO4∶Dy3x+晶粒的生长。当Dy3+的掺入量为1%(摩尔分数)时,其在480nm(蓝)和575nm(黄)的发射强度达到最大;随着Dy3+浓度的增加,其特征发射峰(480nm和575nm)强度反而逐渐下降。     

Properties of Nd3+-doped and undoped tetragonal PbWO4, NaY(WO4)2, CaWO4, and undoped monoclinic ZnWO4 and CdWO4 as laser-active and stimulated raman scattering-active crystals

Spectroscopic, laser, and chi((3)) nonlinear optical properties of tetragonal PbWO(4), NaY(WO(4))(2), CaWO(4), and monoclinic CdWO(4) and ZnWO(4) were investigated. Particular attention was paid to Nd(3+)-doped and undoped PbWO(4) and NaY(WO(4))(2) crystals. Their absorption and luminescence intensity characteristics, including the peak cross sections of induced transitions, were determined. Pulsed and continuous-wave lasing in the two 4F(3/2)-->4I(11/2) and 4F(3/2)-->4I(13/2) channels was excited. For these five tungstates, highly efficient (greater than 50%) multiple Stokes generation and anti-Stokes picosecond generation were achieved. All the observed scattered laser components were identified. These results were analyzed and compared with spectroscopic data from spontaneous Raman scattering. A new crystalline Raman laser based on PbWO(4) was developed for the chi((3)) conversion frequency of 1-microm pump radiation to the first Stokes emission with efficiency up to 40%. We classify all the tungstates as promising media for lasers and neodymium-doped crystals for self-stimulated Raman scattering lasers.     

溶胶—凝胶法制备（Pb,Cd,La）TiO3薄膜及其特性

采用溶胶－凝胶法及均胶工艺,分别在石英玻璃和硅单晶上制备（Ｐｂ,Ｃｄ,Ｌａ）ＴｉＯ２薄膜。用ＳＥＭ分析薄膜的形貌,用ＦＴ－ＩＲ及ＤＴＡ等技术对ＰＣＬＴ薄膜及凝胶粉晶化情况进行分析。用ＸＲＤ对不同基片、不同厚度薄膜成相的影响进行了分析讨论。     

Vacuum-deposited films of mesogen of 4-n-pentyl-4″-cyano-p-terphenyl: their electronic spectra and molecular aggregate structures

Absorption and fluorescence spectra of 4-n-pentyl-4″-cyano-p-terphenyl (5CT) films deposited on hydrophilic and hydrophobic quartz substrates were measured and compared with those of its various solutions and of its neat forms (crystalline, liquid crystal, and isotropic phases). Further, these spectra were compared with those of 4-n-alkoxy-4′-cyanobiphenyls (nOCB, n=8, 9, 10, 12), which had been studied in detail already. The absorption and fluorescence spectra of the 5CT-deposited films were almost independent of substrate property and deposition temperature. This behavior was different from those observed for nOCB. The absorption spectra differed from those of its solution samples and suggested that cyanoterphenyl groups of 5CT molecules in the deposited films form H-aggregate-like structures with their long axes parallel to each other and relatively perpendicular to the stacking direction in the deposited films. The fluorescence spectra were also different from those of its neat and solution samples. Surface morphology of the deposited films was also investigated using atomic force microscopy (AFM). AFM images showed that the deposited films consisted of a number of small plate crystals, which was consistent with H-aggregate-like structures of cyanoterphenyl groups, and that the small plate crystals transformed to needle ones with time. The structural transformation correlated with the absorption and fluorescence spectral changes with time. The deposition processes of 5CT as revealed by in situ fluorescence spectra during deposition were simple compared with those of nOCB and are discussed on the basis of the in situ fluorescence spectra and the AFM images.     

CVD growth and characterization of 3C-SiC thin films

Cubic silicon carbide (3C-SiC) thin films were grown on (100) and (111) Si substrates by CVD technique using hexamethyldisilane (HMDS) as the source material in a resistance heated furnace. HMDS was used as the single source for both Si and C though propane was available for the preliminary carbonization. For selective epitaxial growth, patterned Si (100) substrates were used. The effect of different growth parameters such as substrate orientation, growth temperature, precursor concentration, etc on growth was examined to improve the film quality. The surface morphology, microstructure and crystallinity of grown films were studied using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and X-ray photoelectron spectroscopy (XPS).     

Opaline films on patterned substrates by a simple self-assembly method

A simple method for the preparation of opaline films on flat and patterned glass substrates was investigated. Opaline films and opal micro-channels were obtained by a solvent-evaporation-induced self-assembly process. Scanning electron microscopy (SEM) and optical transmission spectroscopy have been used to investigate the structural quality of the films and optical band gap.     

Synthesis and characterization of Eu3+, Ti4+ @ ZnO organosols and nanocrystalline c-ZnTiO3 thin films aiming at high transparency and luminescence

Abstract

By exploiting colloidal properties, such as transparency, rheology and versatile chemistry, we propose to synthesize new photonic nanomaterials based on colloidal solutions and thin films. This contribution highlights our efforts to elaborate and to characterize nanostructures based on the ZnO–TiO₂ system. Using a recently developed sol–gel route to synthesize new Ti⁴⁺@ZnO organosols, we were able to prepare, at relatively low temperature (400 °C) and short annealing time (15 min), highly transparent, luminescent, nanocrystalline Eu³⁺ doped c-ZnTiO₃ thin films. The organosols and thin films were characterized with UV-visible-near infrared absorption, ellipsometry, photoluminescence spectroscopy, dynamic light scattering, x-ray diffraction and scanning electron microscopy.     

Synthesis and characterization of Eu3+, Ti4+ @ ZnO organosols and nanocrystalline c-ZnTiO3 thin films aiming at high transparency and luminescence

By exploiting colloidal properties, such as transparency, rheology and versatile chemistry, we propose to synthesize new photonic nanomaterials based on colloidal solutions and thin films. This contribution highlights our efforts to elaborate and to characterize nanostructures based on the ZnO–TiO₂ system. Using a recently developed sol–gel route to synthesize new Ti⁴⁺@ZnO organosols, we were able to prepare, at relatively low temperature (400 °C) and short annealing time (15 min), highly transparent, luminescent, nanocrystalline Eu³⁺ doped c-ZnTiO₃ thin films. The organosols and thin films were characterized with UV-visible-near infrared absorption, ellipsometry, photoluminescence spectroscopy, dynamic light scattering, x-ray diffraction and scanning electron microscopy.     

Micropatterning of emitting layers by microcontact printing and application to organic light-emitting diodes

The microcontact printing (μCP) technique, which is a simple and low damage fabrication technique for thin films, was successfully applied to fabricate patterned emitting layers such as polyfluorene (PF). We fabricated micropatterns by transferring dried and uniform thin films, and observed strong electroluminescence (EL) from the fabricated organic light-emitting diodes (OLEDs) with the patterned emitting layers. The performance of the fabricated device was superior to that of a conventionally fabricated device. This demonstrates the well-controlled interfaces achieved by μCP. Furthermore, we succeeded in fabricating OLEDs with multiple emitting layers. These results show that this technique is promising for application to cost-effective, high luminance and multicolored OLED displays.     

Molten salt synthesis and luminescent properties of YVO4:Ln (Ln = Eu3+, Dy3+) nanophosphors

Eu3+ and Dy(3+)-doped YVO4 nanocrystallites were successfully prepared at 400 degrees C in equal moles of NaNO3 and KNO3 molten salts. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, transmission electronic microscopy (TEM), photoluminescence (PL) spectrum and lifetime were used to characterize the nanocrystallites. XRD results demonstrate that NaOH concentration and annealing temperature play important roles in phase purity and crystallinity of the nanocrystallites, the optimum NaOH concentration and annealing temperature being 6:40 and 400 degrees C respectively. TEM micrographs show the nanocrystallites are well crystallized with a cubic morphology in an average grain size of about 18 nm. Upon excitation of the vanadate group at 314 nm, YVO4:Eu3+ and YVO4:Dy3+ nanocrystallites exhibit the characteristic emission of Eu3+ and Dy3+, which indicates that there is an energy transfer from the vanadate group to the rare earth ions. Moreover, the structure and luminescent properties of the nanocrystallites were compared with their bulk counterparts with same composition in detail.     

Molten salt synthesis and luminescent properties of YVO4:Ln (Ln = Eu3+, Dy3+) nanophosphors

Eu3+ and Dy(3+)-doped YVO4 nanocrystallites were successfully prepared at 400 degrees C in equal moles of NaNO3 and KNO3 molten salts. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, transmission electronic microscopy (TEM), photoluminescence (PL) spectrum and lifetime were used to characterize the nanocrystallites. XRD results demonstrate that NaOH concentration and annealing temperature play important roles in phase purity and crystallinity of the nanocrystallites, the optimum NaOH concentration and annealing temperature being 6:40 and 400 degrees C respectively. TEM micrographs show the nanocrystallites are well crystallized with a cubic morphology in an average grain size of about 18 nm. Upon excitation of the vanadate group at 314 nm, YVO4:Eu3+ and YVO4:Dy3+ nanocrystallites exhibit the characteristic emission of Eu3+ and Dy3+, which indicates that there is an energy transfer from the vanadate group to the rare earth ions. Moreover, the structure and luminescent properties of the nanocrystallites were compared with their bulk counterparts with same composition in detail.     

Effect of substrate patterning on hydroxyapatite sol-gel thin film growth

The effect of substrate patterning on hydroxyapatite (HA) sol-gel thin film growth is investigated. Sol-gel derived HA was spun onto wet and dry etched micro-patterned titanium substrates to obtain thin films of thickness ~ 400 nm. The amorphous films were made crystalline by firing at temperatures ranging from 650 to 850 °C for 5 min. Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), and atomic force microscopy (AFM) were used to characterize the films. Crystal sizes calculated from XRD data show that films on patterned substrates contained larger grains than those on un-patterned substrates. The films on wet etched substrates contained larger grains than the films on dry etched substrates. AFM results confirm XRD results. A marked difference between the films on patterned and unpatterned substrates was observed, with those on the patterned substrates being much rougher than those on the unpatterned substrates. The films inside the channels contained larger grains than those outside of channels, on the polished, unetched portion of the substrate.     

Synthesis, characterization, and enhanced luminescence of CaWO4:Eu3+/SBA-15 composites

Considering the combination of lanthanide-doped CaWO₄ nanophosphor and mesoporous matrix may contribute to superior luminescent properties, CaWO₄:Eu³⁺/SBA-15 composites were successfully synthesized in a mild condition. The physicochemical properties of the resultant composites were carefully characterized by X-ray diffraction, high-resolution transmission electron microscopy, inductive coupled plasma optical emission spectroscopy (ICP), N₂ adsorption–desorption, Fourier transform infrared spectroscopy, and luminescence spectra. It’s found that the incorporation of CaWO₄:Eu³⁺ showed no obvious impact on the ordered mesostructure of the host matrix SBA-15, which, however, led to a decrease of BET surface area from 836 to 187 m² g⁻¹ for pure SBA-15 and CES (0.5), respectively. ICP results indicated that the real loaded amount of CaWO₄:Eu³⁺ in SBA-15 host was lower than the initial molar ratios (x) of CaWO₄:Eu³⁺ to SBA-15 for all samples. The maximum loaded level of CaWO₄:Eu³⁺ in SBA-15 is about 27.3 %. Moreover, the real Eu³⁺ dopant concentration increased with the initial molar ratios (x), which showed a maximum of about 6.51 % at x = 0.25. The resultant CaWO₄:Eu³⁺/SBA-15 composites exhibited enhanced-luminescent properties than that of pure CaWO₄:Eu³⁺ nanoparticles, which can be mainly attributed to the variation of Eu³⁺ dopant concentration and the host-protect effect through interaction between guest molecules and host matrix. The available large surface area, pore volume, and superior luminescent properties would facilitate future applications for the composites.     

Selective atomic layer deposition of metal oxide thin films on patterned self-assembled monolayers formed by microcontact printing

We demonstrate a selective atomic layer deposition of TiO2, ZrO2, and ZnO thin films on patterned alkylsiloxane self-assembled monolayers. Microcontact printing was done to prepare patterned monolayers of the alkylsiloxane on Si substrates. The patterned monolayers define and direct the selective deposition of the metal oxide thin films using atomic layer deposition. The selective atomic layer deposition is based on the fact that the metal oxide thin films are selectively deposited only on the regions exposing the silanol groups of the Si substrates because the regions covered with the alkylsiloxane monolayers do not have any functional group to react with precursors.