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ABSTRACT In this study, a series of LaNbTiO6:RE3+ (RE = Tb, Dy, Ho) down-converting phosphors were synthesized using a modified sol-gel combustion method, and their photoluminescence (PL) properties were investigated as a function of activator concentration and annealing temperature. The resultant particles were characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, UV/Vis diffuse reflectance spectroscopy and PL spectra. The highly crystalline LaNbTiO6:RE3+ (RE = Tb, Dy, Ho) phosphors with an average size of 200-300 nm obtained at 1100°C have an orthorhombic aeschynite-type structure and exhibit the highest luminescent intensity in our study range. The emission spectra of LaNbTiO6:RE3+ (RE = Tb, Dy, Ho) phosphors under excitations at UV/blue sources are mainly composed of characteristic peaks arising from the f-f transitions of RE3+, including 489 nm (5D4 → 7F6) and 545 nm (5D4 → 7F5) for Tb3+, 476 and 482 nm (4F9/2 → 6H15/2) and 571 nm (4F9/2 → 6H13/2) for Dy3+, and 545 nm (5F4 + 5S2 → 5I8) for Ho3+, respectively. The luminescent mechanisms were further investigated. It can be expected that these phosphors are of intense interest and potential importance for many optical applications. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

CdTe0.5Se0.5/Cd0.5Zn0.5S core/shell quantum dots (QDs) with a tunable photoluminescence (PL) range from yellow to dark red (up to a PL peak wavelength of 683 nm) were fabricated using various reaction systems. The core/shell QDs created in the reaction solution of trioctylamine (TOA) and oleic acid (OA) at 300 °C exhibited narrow PL spectra and a related low PL efficiency (38%). In contrast, the core/shell QDs prepared in the solution of 1-octadecene (ODE) and hexadecylamine (HDA) at 200 °C revealed a high PL efficiency (70%) and broad PL spectra. This phenomenon is ascribed that the precursor of Cd, reaction temperature, solvents, and ligands affected the formation process of the shell. The slow growth rate of the shell in the solution of ODE and HDA made QDs with a high PL efficiency. Metal acetate salts without reaction with HDA led to the core/shell QDs with a broad size distribution. [ABSTRACT FROM AUTHOR]

ABSTRACT A new ion sensor based on hybrid SiO2-coated CdTe nanocrystals (NCs) was prepared and applied for sensitive sensing of Cu2+ and Ag+ for the selective quenching of photoluminescence (PL) of NCs in the presence of ions. As shown by ion detection experiments conducted in pure water rather than buffer solution, PL responses of NCs were linearly proportional to concentrations of Cu2+ and Ag+ ions < 3 and 7 uM, respectively. Much lower detection limits of 42.37 nM for Cu2+ and 39.40 nM for Ag+ were also observed. In addition, the NC quenching mechanism was discussed in terms of the characterization of static and transient optical spectra. The transfer and trapping of photoinduced charges in NCs by surface energy levels of CuS and Ag2S clusters as well as surface defects generated by the exchange of Cu2+ and Ag+ ions with Cd2+ ion in NCs, resulted in PL quenching and other optical spectra changes, including steady-state absorption and transient PL spectra. It is our hope that these results will be helpful in the future preparation of new ion sensors. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Hydrophobic oleic acid-capped CdSe/Cd x Zn1−x S core/shell quantum dots (QDs) with high photoluminescence (PL) efficiency of 62% and a PL peak wavelength of 602nm were assembled in SiO2 particles through a novel silanization technique. Ligand exchange (3-mercaptopropyltrimethoxysilane (MPS) instead of oleic acid) occurred via the connection of mercapto groups and QDs when MPS was added in the toluene solution of the QDs. After being silanized using MPS, partially hydrolyzed tetraethyl orthosilicate (TEOS) was attached to the surface of the silanized QDs. The hydrophobic CdSe/Cd x Zn1−x S QDs were then transferred from toluene phase to water phase by the hydrolysis of TEOS through the addition of ethanol, ammonia, and water. Further hydrolysis and condensation of the TEOS and MPS causes them to form assemblies in the water phase. MPS is crucial for proper assembly of the QDs in SiO2 particles and for controlling the size of resulting SiO2 particles. The resulting SiO2 particles exhibited tunable diameters from several tens to 100nm. After being encapsulated in SiO2 particles, the QDs revealed a PL efficiency of 25%. Because of the resulting SiO2 particles encapsulating multiple hydrophobic CdSe/Cd x Zn1−x S QDs and having a functional surface (mercapto group), they are applicable to bio-probes. [Copyright &y& Elsevier]

Abstract: A facile method has been developed to encapsulate Fe3O4 nanocrystals (NCs) in morphology-tunable fibers (belt-like, solid, and tubal) by using a sonochemistry driven synthesis and a subsequent reflux procedure. By adapting the use of tetraethyl orthosilicate, ammonia, Cd2+, and thiolglycolic acid (TGA) to an ultrasound-driven synthesis, the Fe3O4 NCs were coated with a thin composite shell. Supersonic treatment plays an important role to prevent the agglomeration of the Fe3O4 NCs in an alkaline condition. The composite shell became thicker due to the deposition of SiO2 monomers, Cd–TGA clusters, Cd2+, and free TGA molecules during reflux. In addition, these composite shell-coated Fe3O4 NCs were assembled in composite fibers which were created by the growth of Cd–TGA clusters and the deposition of SiO2 monomers. The Fe3O4 NCs mono-dispersed in fibers revealed superparamagnetic behavior. The magnetic saturation value of tubal fibers is lower than those of belt-like and solid fibers. These fibers with Fe3O4 NCs would be utilizable for further application. The strategy described here should give a useful enlightenment for the design and fabrication of morphology-tunable fibers with functional NCs. [ABSTRACT FROM AUTHOR]

Abstract: Eu3+ doped yttrium zirconate ((Y1−x Eu x )2Zr2O7) nanocrystals were synthesized by a simple sol–gel combustion method, and characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), UV–vis absorption and photoluminescence (PL) spectroscopy. Photoluminescence spectra of (Y1−x Eu x )2Zr2O7 (x =0.005–0.15) show multi-peaks corresponding to the f–f transitions 5 D 0–7 F J (J =1, 2, 3, 4 and 5) of Eu3+. Both the 5 D 0–7 F 1 magnetic dipole transition and the 5 D 0–7 F 2 electric dipole transition are intense and the 5 D 0–7 F 2 emissions split into several peaks depending on the doping concentration. The fine structure of the PL spectra is related to host lattice and the local situation around Eu3+. [Copyright &y& Elsevier]

Abstract: A series of rare-earth zirconate RE2Zr2O7 nanocrystals (RE=La, Nd, Eu and Y) were prepared by a simple combustion method. These compounds possess either a pyrochlore structure (P-RE2Zr2O7) or a defect fluorite structure (F-RE2Zr2O7), which depends on the ionic radius of RE3+. The photoluminescence (PL) property of the as-prepared RE2Zr2O7 nanocrystals was studied, and the observed emissions in the UV and visible range were attributed to different transition mechanisms for RE2Zr2O7 with different RE ion. A PL mechanism has been proposed, associated with the transition between the valence band and a mid-gap state related to oxygen vacancies. Divalent Pb ions were introduced into RE2Zr2O7 nanocrystals and the luminescence of the Pb2+-doped samples was also recorded for comparison. The PL property of RE2Zr2O7 was found to be intimately related to their intrinsic defect structure, and PL was thought as a new method to estimate the degree of disorder in the A2B2O7 structure (from pyrochlore structure to defect fluorite structure). [Copyright &y& Elsevier]

Abstract: A facile and energy saving sol–gel combustion method has been used to prepare La2Zr2O7 nanocrystallines. The pyrochlore La2Zr2O7 nanocrystals have been obtained at a relatively low temperature with the grain size ranging from 45 to 70nm. Eu3+ and Dy3+ have been introduced into the La2Zr2O7 crystal structure, respectively, and the intense photoluminescence was observed. The relative intensity of electric dipole transition and magnetic dipole transition is considered for luminescence emission both of Eu3+ and Dy3+. The dependence of luminescence intensity on dopant concentration and the effect of Dy3+ co-doping on Eu3+ luminescence are also discussed. [Copyright &y& Elsevier]

Abstract: Eu3+-doped SrZrO3 nanocrystals with a size of about 10nm were synthesized by a simple sol–gel combustion method, and characterized by X-ray diffraction, transmission electron microscopy and photoluminescence spectroscopy. The nanocrystalline intend to assemble to a porous morphology. Both intrinsic defects related and activator luminescence were observed. The red emission of Eu3+ is intense and the spectra show a minor difference with different excitation wavelengths. [Copyright &y& Elsevier]

Abstract: The oxidation behaviour of nanometre and micrometre sized Al2O3–TiC–Co composites is investigated at 800–1000°C in air for 25h. The oxidation resistance of nanometre sized samples is better than of micrometre sized. Phase compositions and microstructures were studied by XRD and SEM. The values of general rate constant k and oxidation exponent n are dependent on oxidation temperature and composites. The oxidation kinetics followed a rate that is slightly faster than the parabolic-rate law at 800–1000°C. The activation energy of the nanometre sized is higher than of micrometre sized in the range of 800–1000°C. [Copyright &y& Elsevier]

Abstract: CdTe nanocrystals (NCs) were coated with a hybrid SiO2 shell containing CdS-like clusters by a facile reflux. These hybrid SiO2-coated CdTe NCs exhibited tunable photoluminescence (PL) and high fluorescence quantum yields (QYs) up to 70% (the QY of initial CdTe NCs is 24%) due to the CdS-like cluster in the SiO2 shell nearby the CdTe core. The average fluorescence lifetime of the hybrid SiO2-coated NCs and the CdTe NCs are 36 and 25ns, respectively. Because increased fluorescence QYs and slightly blue-shifted PL peak wavelength for these hybrid NCs were observed after the removing of TGA and Cd2+, the hybrid SiO2 shell can sufficiently passivate PL, improve chemical stability, and prevent the surface deterioration of the CdTe NCs. This is crucial for applications in biolabeling and optoelectronic devices. [Copyright &y& Elsevier]

ZnO flowers consisting of single crystal nanosheets with exposed { 1   1 ¯   0   0 } facets were fabricated from trisodium citrate via hydrothermal at 180 °C. The single crystal nanosheet has the thickness of about 70 nm and a well-crystalline structure with dominant surfaces as { 1   1 ¯   0   0 } planes. The site-specific nucleation-growth process contributes to the formation of hierarchical flower-like ZnO structures. The ZnO flowers exhibited white emission. The visible emission gradually decreased with time and the UV emission suggests that the recombined rate of photogenerated electrons and holes of samples varied with the synthesis parameters. The ZnO flowers displayed an enhanced photocatalytic performance compared with ZnO microspheres. The maximized exposure of the reactive { 1   1 ¯   0   0 } facets also favors the enhanced photocatalytic performance. Additionally, the special loose structural feature with an open microstructure has more important influences on the photocatalytic activity than specific surface area. [ABSTRACT FROM AUTHOR]

Highlights: [•] YNbTiO6-based phosphors were synthesized by a sol–gel combustion method. [•] The annealing temperature plays the key role of PL properties and particle size. [•] Luminescence of Mn2+, Er3+, and Dy3+-doped YNbTiO6 host was achieved. [•] Luminescent mechanism of Er3+ or Dy3+-doped samples is dipole–dipole interaction. [•] Mn2+ →Er3+ (Dy3+) energy transfers were observed for co-doped phosphors. [Copyright &y& Elsevier]

Abstract: The oxidation behavior of nano-sized Al2O3–TiC–Co composite sintered at different temperature was investigated at 200–1000°C in air for 25h. Microstructures and phase compositions of oxidation surfaces were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results indicated that the oxidation reaction would take place when oxidation temperatures are 800°C and 1000°C. The oxidation resistance of Al2O3–TiC–Co composite increased with the sintering temperature rising when the sample was oxidized at 800°C and 1000°C. The mechanism of oxidation has been analyzed using thermodynamic and kinetics considerations. The oxidation kinetics follows a rate that is faster than the parabolic rate law at 800°C and 1000°C. The activation energy of the composite for oxidation in the range of 800°C to 1000°C was found to be 142.21kJ/mol. [Copyright &y& Elsevier]

Abstract: Undoped and Eu3+-activated Bi3TiNbO9 (BTNO) nanophosphors have been successfully synthesized by sol–gel combustion method. The effects of thermal annealing on the phase structure and crystallinity, morphology and UV–vis absorption of BTNO particles were investigated. Photoluminescence (PL) properties show that a broad blue emission was detected for BTNO nanoparticles, and the characteristic Eu3+ ion 5D0 → 7F J (J =1, 2, 3, 4) transitions were observed for the doped samples. Further investigation illuminates that the Eu3+ ions substituted for Bi3+ ions at A site in the pseudo-perovskite layers. It can be confirmed from high bright fluorescence image and short decay time that the novel orange-red phosphor has the potential applications in luminescence devices. [Copyright &y& Elsevier]

Abstract: Bi4Ti3O12 thin films with bismuth-layered perovskite structure have been successfully fabricated by means of chemical solution decomposition (CSD) and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and UV–vis spectrophotometry in this study. The photocatalytic activity of Bi4Ti3O12 thin films has been evaluated by photodegrading methyl orange solution, and the optimum processing parameters for the photocatalytic activity have been found. Moreover, it has been found that La-doping can improve the photocatalytic activity of Bi4Ti3O12 thin films and hinder the increase of crystallite sizes during calcination. [Copyright &y& Elsevier]

Abstract: Dopant-free Bi2Ti2O7 thin films with pyrochlore structure and La-doped bismuth titanate thin films have been fabricated by means of chemical solution decomposition, and characterized by X-ray diffraction, atomic force microscopy, scanning electron microscopy and UV–Vis spectrophotometry in this study. Their photocatalytic activities have been evaluated by photodegrading methyl orange solution, and the optimum processing parameters for the highest photocatalytic activity have been found. Moreover, the effects of La-doping on the phase transformation and the photocalalytic activity have been studied. It has been deduced from the experiment result that substituted La3+ ions can act as a stabilizer of Aurivillus phase BLT and a grain–growth inhibitor in BLT thin films. [Copyright &y& Elsevier]

Abstract: Nb2O5 nanorods have been prepared using water/ethanol media. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–visible absorption and photoluminescence spectroscopy. The as-prepared Nb2O5 nanorods appeared to be single pseudohexagonal (TT-Nb2O5) phase. From the photoluminescence spectrum, two emission bands at 407 and 496nm, respectively, were observed. The origin of the luminescence was discussed in detail. [Copyright &y& Elsevier]