Key Engineering Materials Vols. 602-603

Abstract: Lead lanthanum zirconate titanate (PLZT) transparent ceramics have attracted more and more attentions for their unique electrically controlled light scattering effects. By the hot-press sintering method, a series of PLZT (X/70/30) ceramics with different La concentration (7.3, 7.4, 7.45, 7.5, 7.6 mole %) have been synthesized to figure out its influence on the electrically controlled light scattering performances. XRD patterns reveal the formation of a single-phase perovskite structure for all samples. The PLZT (7.3/70/30, 7.4/70/30, 7.45/70/30) samples exhibit a ferroelectric behavior, but with the La concentration increasing, the samples exhibit a tendency of a double hysteresis loop which is due to antiferroelectric phase coexisted. The temperature of maximum dielectric constant (T_m) of the PLZT (X/70/30) ceramics shifts from ~99 °C to ~87 °C with the increasing of La concentration at 1 kHz. All samples exhibit a high transmittance (61%, 0.35 mm) within the wavelength range from visible to near-infrared light. Depending on the La concentration, the light scattering behavior of PLZT ceramics exhibit two main types, in which PLZT (7.45/70/30) promises a unique potential application in laser modulators for its outstanding advantages of less energy consumption and relatively larger contrast ratio.

Abstract: Tin doped indium oxide (ITO) thin films were prepared on IR glass substrates at different oxygen flow rate by ion-assisted electron beam evaporation method, high purity ITO particles (In₂O₃: SnO₂ = 9:1 Wt%) were used as source material. Properties such as microstructure, morphology and mechanical properties were investigated by X-ray diffractometer, SEM and scratch tester, respectively. Meanwhile, lattice constant a, crystal grain size and residual stress situation of films as-deposited were calculated and discussed in detail. The results indicated that all of the films as-deposited were polycrystalline and represented [111] preferential orientation. With the increasing of the oxygen flow rate, grain size and surface roughness of films as-deposited decreased, and inner stress remained in film increased. There were two types of failure mode occurred in ITO films according to different stress situation. Relative high level of residual stress improved the mechanical properties of ITO films in a certain extent.

Abstract: The subject of this work was to study the photoluminescence characteristics of nanoZnO and SiO₂ powders into Zn₂SiO₄ phosphor, and to achieve better control on grain size and grain shape than traditional powder. The manganese elements were used to replace Zn₂SiO₄ defects and to achieve better control on grain size and grain shape than traditional powder. With different sintering atmosphere conditions, the effect of the photoluminescence intensity due to sintering temperature and the concentration of activator were be discussed by the X-Ray diffraction, SEM and TEM were utilized in the characterization of phase purity and microstructure of phosphor particles.

Abstract: The shifted band and high intensity of the photoluminescence characteristics for RTA-treated Si⁺-implanted SiO₂ thin films for 400-nm-thick thickness using post-CTA processing were discussed and investigated. The samples were treated in the temperature of 1150°C and 20s RTA processing under dry nitrogen atmosphere. The PL band of thin films obtained was 1.7 eV. However, the PL intensity of thin films was continuous decreased for RTA annealing time increased. In this study, the PL band for RTA-treated thin films using 1h post-CTA processing was shifted from 1.5 to 1.67 eV. In addition, the PL intensity of the thin films was increased under the post-CTA annealing time increased to 60s. From the plan-view of the HRTEM image, the Si nanocrystals of the RTA-treated thin films using post-CTA processing were observed. These results were related to the presence and variation of silicon Si nanocrystals embedded in thin films.

Abstract: Two dimensional nanophosphors of high quality play an important role in the miniaturization and intelligentization of opto-electronic components. In this present work, ultra-large (30μm) single crystals of (Y_0.95Eu_0.05)₂(OH)₅NO₃·nH₂O layered rare earth hydroxide (LRH) with a hexagonal shape have been synthisized via autoclaving the rare-earth nitrate/NH₄OH reaction system in the presence of ammonium nitrate (NH₄NO₃). The nitrate ions, existing in the interlayer gallery of layered rare earth hydroxide, exhibit facile exchanges with oleate anions by hydrothermal anion exchange. Furthermore, the interlayer distance can thus be expanded from ~0.9 nm for the pristine LRHs to ~3.60 nm for the intercalated ones, which are then efficiently delaminated into unilamellar nanosheets with a lateral size of 10μm and a thickness of ~1.50 nm. The obtained nanosheets are single crystaline. Highly [11 oriented, dense (Y_0.95Eu_0.05)₂O₃ phosphor films with excellent optical transparency and a greatly enhanced luminescence intensity have been constructed via self-assembly of ultra-large unilamellar LRH nanosheets, followed by proper annealing.

Abstract: Ln (OH)₃(Ln=La_0.95Eu_0.05) nanowires have been successfully synthesized through hydrothermal reaction, without using any template, from mixed solutions of the component nitrates. It was shown that neither solution pH (7.5-13) nor hydrothermal temperature (120 and 150 °C) significantly influences the phase structure and particle morphology of the product. The resultant Ln (OH)₃ nanowires are of uniform dimension and good dispersion. A homogeneous Ln₂O₃ solid solution was yielded by calcining the hydroxide nanowires in the air at 800 oC. Under 285 nm excitation, the Ln₂O₃ phosphor exhibits the characteristic red emission of Eu³⁺ at ~630 nm and show emission behaviors clearly dependent on the calcination temperature, which were investigated in detail.

Abstract: Ce³⁺ activated terbium aluminum garnet ((Tb_1-xCe_x)₃Al₅O₁₂, 0≤x≤0.05) phosphors have been converted from their precursors synthesized via co-precipitation from mixed solutions of aluminum and rare earth nitrates with ammonium hydrogen carbonate (AHC) as the precipitant. Detailed characterizations of the precursors and the phosphor oxides were performed by the combined techniques of X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FE-SEM), differential scanning calorimetry/thermogravimetry (DSC/TG), and photoluminescence spectroscopy. The co-precipitated precursors possess a general composition of (NH₄)_x(Tb,Ce)₃Al₅(CO₃)_y(OH)_z·nH₂O, and the particles, having diameters of about 50nm, are well dispersed. Calcining the precursors at 1000°C for 4 h in the air and then reducing in a hydrogen atmosphere at 1000°C for 2 h yielded a phase pure garnet solid-solution of (Tb_1-xCe_x)₃Al₅O₁₂. The cubic lattice of garnet allows the Ce³⁺ activators to reside at the dodecahedral interstitial sites. The resultant garnet phosphors with various Ce³⁺ contents exhibit nearly identical positions of the PLE/PE bands, but significantly different intensities. Upon blue-light excitation at 470nm, the garnet phosphors exhibit broad band emissions peaking at 560nm. The garnet phosphors show a luminescence quenching concentration of 1.5at% for Ce³⁺.

Abstract: The metastable garnet lattice of Gd₃Al₅O₁₂ (GdAG) was effectively stabilized via doping with significantly smaller Lu³⁺, and based on which (Gd,Lu)AG:Yb/Ho was developed in this work as a new type of upconversion phosphor. The phosphor particles calcined from the precursors synthesized via carbonate precipitation were observed to have good dispersion and fairly uniform morphologies. Optical spectroscopy found that the [(Gd_1-xLu_x)_0.948Yb_0.05Ho_0.002]₃Al₅O₁₂ (x=0.1-0.5) garnet powders exhibit a green emission centered at ~543 nm (the ⁵F₄,⁵S₂⁵I₈ transition of Ho³⁺) and a red emission centered at ~668 nm (the ⁵F₅⁵I₈ transition of Ho³⁺) under laser excitation at 978 nm. The upconversion emission intensity was found to decrease with increasing Lu³⁺ doping. Meanwhile, the dependence of up-conversion emission intensity on the pumping power was measured and the up-conversion mechanism was discussed in detail. The Yb/Ho codoped (Gd,Lu)AG garnet system developed herein may potentially be used as a new type of luminescent material.

Abstract: TiO_x thin films were deposited by RF magnetron sputtering with TiO_x (x<2) target at varied substrate temperatures. The composition and microstructure of the films was characterized by grazing incidence X-ray diffraction, scanning electron microscopy and Raman spectroscopy, which revealed that the films deposited at low temperatures were amorphous, and as the temperature increased up to 600 °C, the prepared films became crystalline and a TiO₂ anatase phase was identified. Also the electrical resistivity of the as-prepared TiO_x films was investigated as a function of the deposition temperature. The result indicates that with the raise of substrate temperature, the electrical resistivity of the deposited films decreased sharply.

Abstract: Silver decorated TiO₂ nanoparticles (Ag@syn-TiO₂, Ag@P25) were synthesized by photoreducing Ag⁺ species in the presence of the synthetized TiO₂ (syn-TiO₂) nanocrystals or P25. The samples obtained were characterized by XRD, XPS, UV-vis and TEM. The XRD results showed the syn-TiO₂ nanoparticles were pure anatase, and the P25 nanoparticles were the mixture of antase and rutile. The TEM observations and XPS spectra indicated that Ag species anchored on the surfaces of syn-TiO₂ nanoparticles as Ag⁰ and AgO nanoclusters (NCs). The Ag NCs have a size range of 13 nm and the AgO NCs have a size range of 1015 nm. The Ag NCs on the surface of P25 have a size range of 57 nm, and no AgO species were found. The photocatalytic performance of the Ag@syn-TiO₂ and Ag@P25 samples was evaluated by degradating Rhodamine B (RhB) under visible-light irradiation (λ ≥ 420 nm). The results indicated that the phases and morphologies of TiO₂ nanocrystals have effects on their photocatalytic properties, and that the syn-TiO₂ nanocrystals wiht the pure anatase are more active than P25 with the mixture of antase and rutile in RhB degradation. The possible mechanisms were discussed.