Crystallinity and morphology dependent luminescence of Li-doped Y2−xGdxO3:Eu thin film phosphors

The influence of lithium doping on the crystallization, the surface morphology, and the luminescent properties of pulsed laser deposited Y_2−xGd_xO₃:Eu³⁺ thin film phosphors was investigated. The crystallinity, the surface morphology, and the photoluminescence (PL) of films depended highly on the Li-doping and the Gd content. The relationship between the crystalline and morphological structures and the luminescent properties was studied, and Li⁺ doping was found to effectively enhance not only the crystallinity but also the luminescent brightness of Y_2−xGd_xO₃:Eu³⁺ thin films. In particular, the incorporation of Li and Gd into the Y₂O₃ lattice could induce remarkable increase in the PL. The highest emission intensity was observed Li-doped Y_1.35Gd_0.6O₃:Eu³⁺ thin films whose brightness was increased by a factor of 4.6 in comparison with that of Li-doped Y₂O₃:Eu³⁺ thin films.     

Synthesis and room temperature photoluminescence of ZnO/CTAB ordered layered nanocomposite with flake-like architecture

Flake-like ZnO/surfactant ordered layered nanocomposite has been synthesized by self-assembly at room temperature with the presence of cetyltrimethylammonium bromide (CTAB, CH₃(CH₂)₁₅N⁺(CH₃)₃Br⁻) surfactant. The procedure described in this study is attractive since it gives high yields of ordered layered nanocomposite with flake-like architecture. XRD results showed the formation of a layered structure with two layered spacings ca. 18.56 Å. SEM and FT-IR spectroscopy were used to further characterize ZnO/CTAB nanolayered composite. The ZnO/CTAB-ordered layered nanocomposite exhibits the room temperature photoluminescence (RTPL) characteristics. It is inferred that the RTPL of ZnO/CTAB-layered nanocomposite might be induced by the interfacial effect between the ZnO and the surfactant.     

Microstructure and tribological performance of self-lubricating diamond/tetrahedral amorphous carbon composite film

In order to smooth the rough surface and further improve the wear-resistance of coarse chemical vapor deposition diamond films, diamond/tetrahedral amorphous carbon composite films were synthesized by a two-step preparation technique including hot-filament chemical vapor deposition for polycrystalline diamond (PCD) and subsequent filtered cathodic vacuum arc growth for tetrahedral amorphous carbon (ta-C). The microstructure and tribological performance of the composite films were investigated by means of various characterization techniques. The results indicated that the composite films consisted of a thick well-grained diamond base layer with a thickness up to 150 μm and a thin covering ta-C layer with a thickness of about 0.3 μm, and sp³-C fraction up to 73.93%. Deposition of a smooth ta-C film on coarse polycrystalline diamond films was proved to be an effective tool to lower the surface roughness of the polycrystalline diamond film. The wear-resistance of the diamond film was also enhanced by the self-lubricating effect of the covering ta-C film due to graphitic phase transformation. Under dry pin-on-disk wear test against Si₃N₄ ball, the friction coefficients of the composite films were much lower than that of the single PCD film. An extremely low friction coefficient (∼0.05) was achieved for the PCD/ta-C composite film. Moreover, the addition of Ti interlayer between the ta-C and the PCD layers can further reduce the surface roughness of the composite film. The main wear mechanism of the composite films was abrasive wear.     

Enhanced luminescence of GdTaO4:Eu thin-film phosphors by K doping

The effect of K⁺ ions on GdTaO₄:Eu³⁺ thin-film phosphors was investigated in order to improve their luminescent properties. The GdTaO₄:Eu_0.1, K_x thin films were synthesized by sol-gel process, and characterized through measuring their microstructure and luminescence. The results indicated that photoluminescence (PL) intensity of GdTaO₄:Eu³⁺ film was improved remarkably by K doping. There were two maxima in the curve of PL intensity against K⁺ dopant concentration, where one was improved up to 2.1 times at x = 0.001 and the other was enhanced up to 2.7 times at x = 0.05. The first maximum was regarded as the alteration of the local environment surrounding the Eu³⁺ activator by incorporation of K⁺ ions, and the second maximum was due to the flux effect. Additionally, the luminescence increased with the increase of firing temperature from 800 °C to 1200 °C.     

The nonlinear optical property and photoinduced anisotropy of?a?novel azobenzene-containing fluorinated polyimide

A novel azobenzene-containing fluorinated polyimide was synthesized. The nonlinear optical property and photoinduced birefringence of a polyimide thin film were investigated. Large third-order nonlinear refraction (n ₂=−4.49×10⁻¹¹ cm²/W) was observed in the polyimide thin film by carrying out Z-scan measurement. The polyimide thin film exhibited larger nonlinear refraction than that of a mono-azo dye doped PMMA thin film (n ₂=−1.63×10⁻¹² cm²/W). The photoinduced birefringence of the polyimide thin film (▵ n∼10⁻²) under different pump intensities was investigated; it was much larger than that of the mono-azo dye doped PMMA thin film (▵ n∼10⁻³). Moreover, the time constants for birefringence growth and relaxation processes were determined.     

Preparation and characterization of NiFe2O4/NiO composite film via a single-source precursor route

NiFe₂O₄/NiO nanocomposite thin films have been successfully prepared through a facile route using nickel iron layered double hydroxide (NiFe-LDH) as a single-source precursor. This synthetic approach mainly involves the formation of NiFe-LDH film by casting the slurry of NiFe-LDH precursor on the α-Al₂O₃ substrate, followed by high-temperature calcination. The composition, microstructure and properties of the films were characterized in detail by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and vibrating sample magnetometer (VSM). The results indicate that NiFe₂O₄/NiO composite film was composed of granules with diameter less than 100 nm, and the thickness of the film was in the range 1-2 μm. The magnetization of the film can be tuned by alternating the Ni/Fe molar ratio of LDH precursor. In addition, the method developed should be easily extended to fabricate other MFe₂O₄/MO composite film systems with specific applications just by an appropriate combination of divalent/trivalent composition in the precursor of LDHs.     

Synthesis and photophysics of a new deep red soluble phosphorescent iridium(III) complex based on chlorine-methyl-substituted 2,4 diphenyl quinoline

A new iridium complex with a chlorine-methyl-substituted 2,4 diphenyl quinoline, (Cl-MDPQ) ligand has been synthesized. The synthesized iridium metal complex, Ir(Cl-MDPQ)₂(acac) where Cl-MDPQ=chlorine-methyl substituted, 2,4 diphenyl quinoline, acac=acetyl acetone is characterized by employing different techniques such as mass spectrometry, ¹H NMR, DTA/TGA, XRD, and FTIR. The molecular structures of Cl-MDPQ and Ir(Cl-MDPQ)₂(acac) complexes are confirmed by the FTIR spectra. Strong singlet metal-to-ligand charge-transfer (¹MLCT) and triplet metal-to-ligand charge-transfer (³MLCT) absorption peaks at 353 and 437 nm in tetrahydrofuran (THF) are reported in the synthesized complex, respectively. A deep red emitting Ir(Cl-MDPQ)₂(acac) complex at 662 nm is promising for flexible organic devices.     

Highly enhanced photoluminescence and X-ray excited luminescence of Li doped Gd2O3:Eu thin films

Transparent Li-doped Gd₂O₃:Eu³⁺ thin-film phosphors were prepared by a modified sol-gel method. The effect of the Li⁺ ions on luminescent properties of the thin film was investigated. The results indicated that incorporation of Li⁺ ions into Gd₂O₃ lattice could result in a remarkable increase on photoluminescence or X-ray excited luminescence, and the strongest emission was observed from Gd_1.84Li_0.08Eu_0.08O_3−δ film, in which the intensity was increased by a factor of 1.9 or 2.3 in comparison with that of Gd_1.92Eu_0.08O₃ film. And it could be achieved the highest intensity for sintering the Gd_1.84Li_0.08Eu_0.08O_3−δ film at 700 °C. Such a temperature is much lower than the typical solid-state reaction temperature for its powder phosphors. This kind of transparent thin-film phosphors may promise for application to micro X-ray imaging system.     

Evidence for Strong Mixing Between the LC and MLCT Excited States in Some Heteroleptic Iridium (III) Complexes

The synthesis, structure and photophysical properties of series of new luminescent cyclometalated Iridium (III) complexes are reported. The cyclometalated ligand used here is 2-aryl imidazole and the auxiliary ligand is acetyl acetone (acac). The crystal structure of the complex (dmdpi)₂Ir(acac) (5) show that the Iridium(III) ion resides in a distorted octahedral environment. All complexes exhibit bright photoluminescence (PL) at room temperature and (fpdmdmpi)₂Ir(acac) 4 has a high solution PL quantum efficiency of 0.56. The role played by electron releasing and electron withdrawing substituents of the 2-arylimidazole ligands towards the stability of HOMO and how the substituent influences the luminescent behaviour are discussed. Furthermore those substituents have effect on the contribution to mixing between ³(π-π*) and ³(MLCT) for the lowest excited states.     

Characteristic properties of Y2SiO5:Ce thin films grown with PLD

Three different gases (nitrogen (N₂), oxygen (O₂) and argon (Ar)) were used as background gases during the growth of pulsed laser deposition (PLD) Y₂SiO₅:Ce thin films. A Krypton fluoride laser (KrF), 248 nm was used for the PLD of the films on silicon (Si) (1 0 0) substrates. The effect of the background gases on the surface morphology, crystal growth and luminescent properties were investigated. All the experimental parameters, the gas pressure (455 mT), the substrate temperature (600 °C), the pulse frequency (8 Hz), the number of pulses (4000) and the laser fluence (1.6±0.2) J/cm² were kept constant. The only parameter that was changed during the deposition was the ambient gas species. The surface morphology and average particle sizes were monitored with scanning electron microscopy (SEM) and atomic force microscopy (AFM). X-ray diffraction (XRD) and Auger electron spectroscopy (AES) were used to determine the crystal structure and composition, respectively. Cathodo- (CL) and photoluminescence (PL) were used to measure the luminescent intensities for the different phosphor thin films. The nature of the particles, ablated on the substrate, is related to the collisions between the ejected particles and the ambient gas particles. The CL and PL intensities also depend on the particle sizes. A 144 h (coulomb dose of 1.4×10⁴ C cm⁻²) electron degradation study on the thin films ablated in the Ar gas environment resulted in a decrease in the main CL intensity peak at 440 nm and to the development of a new very broad luminescent peak spectra ranging from 400 to 850 nm due to the growth of a SiO₂ layer on the surface.     

Effect of process parameters on surface morphology and characterization of PE-ALD SnO2 thin films for gas sensing

Tin dioxide (SnO₂) thin films were deposited by plasma enhanced-atomic layer deposition (PE-ALD) on Si(1 0 0) substrate using dibutyl tin diacetate (DBTA) ((CH₃CO₂)₂Sn[(CH₂)₃-CH₃]₂) as precursor. The process parameters were optimized as a function of substrate temperature, source temperature and purging time. It is observed that the surface phenomenon of the thin films was changed with film thickness. Atomic force microscopy (AFM) images and X-ray diffraction (XRD) pattern were used to observe the texture and crystallanity of the films. The films deposited for 100, 200 and 400 cycles were characterized by XPS to determine the chemical bonding properties. XPS results reveal that the surface dominant oxygen species for 100, 200 and 400 cycles deposited films are O₂⁻, O⁻ and O²⁻, respectively. The 200 cycles film has exhibited highest concentration of oxygen (O⁻) species before and after annealing. Conductivity studies revel that this film has best adsorption strength to the oxygen ions forming on the surface. The sensor with 200 cycles SnO₂ thin film has shown highest sensitivity to CO gas than other films. A correlation between the characteristics of Sn3d_5/2 and O1s XPS spectra before and after annealing and the electrical behavior of the SnO₂ thin films is established.     

Magnetic properties of disordered ferrite and ilmenite-hematite thin films

We have synthesized thin films of disordered zinc ferrite (ZnFe₂O₄) and ilmenite-hematite (FeTiO₃-Fe₂O₃) solid solution, the former and the latter of which are interesting from the viewpoints of magnetooptics and spintronics, respectively, by utilizing sputtering and pulsed laser deposition methods, and have explored their magnetic, magnetooptical, and electrical properties. Although ZnFe₂O₄ possesses a normal spinel structure as its stable phase, some of the Fe³⁺ ions occupy the tetrahedral as well as the octahedral sites in ZnFe₂O₄ of which the sputtered thin film is composed. Consequently, the as-deposited thin film manifests large magnetization even at room temperature although the magnetic phase transition temperature of the stable phase of ZnFe₂O₄ is as low as 10 K. Also, the thin film exhibits a cluster spin glass transition at a temperature as high as 325 K. Furthermore, the ZnFe₂O₄ thin films exhibit large Faraday effects at a wavelength of 400 nm or so. The ilmenite-hematite solid solution is one of the ferrimagnetic semiconductors. Most of the compositions possess Curie temperatures higher than room temperature, and the type of carrier can be tuned only by changing the composition. We have succeeded in synthesizing solid-solution thin films of various compositions grown epitaxially on sapphire substrates with a (0 0 0 1) plane, and have shown that the thin films are ferrimagnetic semiconductors.     

Ferromagnetism of epitaxially grown CaRu1−xMxO3 (M=Ti, Mn) films

Epitaxial thin films of CaRu_1−xM_xO₃ (M=Ti, Mn) were fabricated on a (0 0 1)-SrTiO₃ substrate by spin-coat method using organometallic solutions (metal alkoxides). Results of X-ray diffraction and transmission electron microscopy indicate that the epitaxial films were grown pseudomorphically so as to align the [0 0 l] axis of the CaRu_1−xM_xO₃ films perpendicular to the (0 0 1) plane of the SrTiO₃ substrate. Ferromagnetism and metal-insulator transition are induced by the substitution of transition metal ions. The occurrence of ferromagnetism was explained qualitatively assuming a TiRu₆ cluster model for CaRu_1−xTi_xO₃ film and a mixed valence model for CaRu_1−xMn_xO₃ film. Ferromagnetism was also observed for layered CaRuO₃/CaMnO₃ film and CaRuO₃/CaMnO₃/CaRuO₃/CaMnO₃ multilayer film and the magnetism was explained by an interfacial exchange interaction model with magnetic Mn³⁺, Mn⁴⁺, and Ru⁵⁺ ions.     

铽配合物——蒙脱土新型复合发光材料的插层组装、表征和发光性能

合成了铽的配合物[TbL] (ClO₄)₃(L: 2, 2, 2', 2'-四[N-苯基-N-苄基(乙酰胺)-2-氧甲基]丁醚), 通过离子交换反应将配离子[TbL]³⁺插层组装到蒙脱土(MMT)层板间, 制备出了新型复合发光材料 [TbL]³⁺-MMT．用元素分析、X射线衍射、傅氏变换红外光谱和紫外-可见光谱对材料进行了表征, 对其荧光性质进行了研究．结果表明, 复合发光材料保持了蒙脱土良好的层柱结构特征和[TbL]³⁺离子的笼状结构特征, [TbL]³⁺离子以单层形式分布于蒙脱土层板间．在紫外光激发下, 复合发光材料发出较强的绿色荧光, 其发射光谱与相应配合物的发射光谱相似．与相应纯配合物比较, 复合发光材料单位质量Tb³⁺的相对荧光强度、荧光单色性和光稳定性有显著改善, 其激发波长向可见光区发生明显位移, 说明插层组装对相应配合物的激发波长有一定的调制作用.     

Luminescence study of SHI irradiated nano semiconductor: Conducting polymer composite

Semiconductor nanoparticle and conducting polymer composite is an interesting class of materials for optoelectronic and photovoltaic device application. We have synthesized a composite of nanocrystalline PbS and conducting polymer MEH-PPV by chemical synthesis and studied the effect of swift heavy ion (SHI) irradiation on the composite material. The irradiation of the composite materials in thin film form is carried out with 120 MeV Si⁺⁹ ion beam at fluences from 5×10¹⁰ to 10¹³ ions/cm². Fluence dependent optical and structural properties have been observed in optical absorption, PL and TEM studies. Reduction of nanoparticle size has been observed after irradiation.     

Synthesis and electronic behaviors of TiO2/carbon clusters/Cr2O3 composite materials

Nano-structured TiO₂/carbon clusters/Cr₂O₃ composite material has been successfully obtained by the microwave treatment of a TiO(acac)/Cr(acac)₃/epoxy resin complex. The compositions of the composite materials were determined using ICP, elemental analysis and surface characterization by SEM-EDX, TEM and XRD. ESR spectral examinations suggest the possibility of an electron transfer in the process of TiO₂ → carbon clusters → Cr₂O₃ with an oxidation site at TiO₂ particles and a reduction site at Cr₂O₃ particles. The preliminary experimental results show that the calcined materials could decompose methylene blue under visible-light irradiation.     

Application of optical and luminescent techniques to the characterization of oxide thin films

The interaction between light and electrons in oxide compounds forms the basis for many interesting and practical effects, which are related to microstructure, energy band, traps, carrier transport and others. Thin films of oxides like WO₃, Ga₂O₃, Y₂O₃ and SrTiO₃ were investigated using various improved optical and luminescent techniques. The home-made systems for optical and luminescent measurements were described in detail. The facilities of photo-Hall and photoconductivity transients have been proven to be powerful tools in the studies, which allow us to perform photoinduced process and relaxation measurements over a wide time range from 10⁻⁸ to 10⁴ s. Furthermore, we extended the measurement capabilities of the commercial luminoscope by using an interferometer system with optical fiber and illuminance meter instead of an optical microscope. The cathodoluminescent measurements can be performed at a relative high pressure (20-60 mTorr) compared to ultra-high-vacuum condition of most commercial products. Luminescent characterization was employed as a probe to study doping ions, oxygen vacancies, trap and/or exciton levels in oxide thin films. Our results suggest that various traps and/or excitons in thin films of WO₃, Ga₂O₃ and SrTiO₃ involve in the process of photoconductivity relaxation and emission.     

Structural and electrical transport properties of ZnxFe3−xO4 thin film deposited on Si (1 1 1) by pulsed-laser deposition

Polycrystalline thin films of Fe_3−xZn_xO₄ (x = 0.0, 0.01 and 0.02) were prepared by pulsed-laser deposition technique on Si (1 1 1) substrate. X-ray diffraction studies of parent as well as Zn doped magnetite show the spinel cubic structure of film with (1 1 1) orientation. The order–disorder transition temperature for Fe₃O₄ thin film with thickness of 150 nm are at 123 K (Si). Zn doping leads to enhancement of resistivity by Zn²⁺ substitution originates from a decrease of the carrier concentration, which do not show the Verwey transition. The Raman spectra for parent Fe₃O₄ on Si (1 1 1) substrate shows all Raman active modes for thin films at energies of T_2g¹, T_2g³, T_2g², and A_1g at 193, 304, 531 and 668 cm⁻¹. It is noticed that the frequency positions of the strongest A_1g mode are at 668.3 cm⁻¹, for all parent Fe₃O₄ thin film shifted at lower wave number as 663.7 for Fe_2.98Zn_0.02O₄ thin film on Si (1 1 1) substrate. The integral intensity at 668 cm⁻¹ increased significantly with decreasing doping concentration and highest for the parent sample, which is due to residual stress stored in the surface.     

Third-order nonlinear optical response of Au-core CdS-shell composite nanoparticles embedded in BaTiO<Subscript>3</Subscript> thin films

Au-core CdS-shell composite nanoparticles were synthesized by a direct self-assembly process and integrated into BaTiO₃ thin films. Characterization by transmission electron microscopy showed that the average diameter of these composite nanoparticles was about 8 nm. Using the femtosecond time-resolved optical Kerr effect method, we investigated the third-order nonlinear optical response of the Au@CdS nanoparticles embedded in the BaTiO₃ thin films at a wavelength of 800 nm. An ultrafast nonlinear response and a large effective third-order nonlinear susceptibility of χ⁽³⁾=7.7×10^-11 esu were observed. We attributed the enhancement of the third-order optical nonlinearity to a localized electric field effect originating from the core-shell structure under off-surface-plasmon resonance conditions. Received: 13 May 2002 / Revised version: 23 October 2002 / Published online: 3 April 2003 RID="*" ID="*"Corresponding author. Fax: +86-21/6510-4949, E-mail: sxqian@fudan.ac.cn     

Fabrication and characterization of suspended single-walled carbon nanotubes

Suspended single-walled carbon nanotubes (SWCNTs) between SiO₂ pillars via a direct lithographic route using a simple mixture of catalyst precursor [Co(III) acetylacetonate, Co(acac)₃] and conventional electron beam resist (ma-N2403) were fabricated. The catalytic electron beam resist (Cat-ER) layer plays dual roles as a catalyst and a resist layer for the growth and alignment of CNTs, respectively. The structure of the grown nanotube was characterized by Raman spectroscopy (633 nm laser excitation). Nanotubes grown from Cat-ER with Co(acac)₃ show the typical Raman spectra of SWCNTs which are characterized by the strong tangential bands near to 1590 cm⁻¹ and radial breathing modes (RBMs) in the low frequency region (<300 cm⁻¹). The calculated diameter of the probed nanotubes individually corresponds to the range 0.86-1.77 nm.