Search

The red-emitting Sr2Si5N8:Eu2+ phosphor with a superior quantum efficiency and suitable emission spectrum has been widely used as a promising down-conversion material in white light-emitting diodes. However, its thermal degradation under high temperature handicaps its large scale application, and therefore must be reduced. Here, we proposed to increase the thermal stability of Sr2Si5N8:Eu2+ by coating a nanometer-order Al2O3 film on each phosphor particle using an atomic layer deposition approach in a fluidized bed reactor. The deposited Al2O3 layer was quite uniform and conformal when using O3 as the oxidizer, and its thickness could be controlled by the dosage type, deposition temperature and cycle numbers, which largely affects the photoluminescence properties and thermal degradation of the title phosphor. Thermal gravimetric analysis results showed that the oxidation temperature of the coated phosphor increased from 700 to 850 °C, suggesting that the coating layer has the function of anti-oxidation. Meanwhile, the coated phosphor particle surface became hydrophobic. Consequently, the thermal degradation of phosphor powders in air at 200 °C was greatly reduced and the stability of the fabricated LEDs with coated powders was also improved. Prospectively, the proposed approach provides a new strategy to improve the thermal stability of other phosphors.

It is critical to reveal how crystalline polarity correlates with the electronic transport properties in polar semiconductors, such as zinc oxide (ZnO), for the development of materials with properties tailored for specific optoelectronic applications. In this paper, we investigate the structure–property relationships in ZnO films by means of tailoring the polarity of homostructural ZnO bilayers that are subjected to an external substrate bias (Vsub) during deposition. Since the probability of incorporating defects and impurities in ZnO depend on the crystalline facet, the polarity of ZnO should be a critical parameter in determining electronic conductivity. The electric conductivity and Hall mobility of the ZnO films deposited under positive Vsub were much higher than those deposited under negative Vsub. Further investigations of the homostructural ZnO bilayer films, where different signs and magnitudes of Vsub were applied, revealed that the polarity is responsible for electronic conductivity of the ZnO...

The β-sialon:Eu 2+ phosphor has superior luminescent properties as an excellent green down-conversion material for white light-emitting diodes. To take advantage of its high chromaticity and apply it to field emission displays (FEDs), the drawback of its electron insulation that impedes the electron transmission when excited by e-beam needs to be solved. In this work, a facile method was adopted to coat conductive In 2 O 3 on the surface of β-sialon:Eu 2+ phosphor, and the influence of In 2 O 3 coating on the cathodoluminescent properties was investigated. The results show that the In 2 O 3 coating contributes to charge elimination and significantly improves the cathodoluminescence (CL) of β-sialon:Eu 2+ . Under 19 kV/1.0 nA e-beam excitation, the In 2 O 3 coated sample shows CL intensity about four times higher than that of the uncoated β-sialon:Eu 2+ . Moreover, no luminescence saturation occurs in coated β-sialon:Eu 2+ , indicating that the In 2 O 3 -coated β-sialon:Eu 2+ would be a promising green emissive material for full-color FEDs.

International audience; We report the photoluminescence (PL) and cathodoluminescence (CL) properties of face-capped [MoXL] (X = Cl, Br, I; L = organic or inorganic ligands) cluster units. We show that the emission of Mo metal atom clusters depends not only on the nature of X and L ligands bound to the cluster and counter-cations, but also on the excitation source. Seven members of the AMoXL series (A = Cs, (n-CH)N, NH) were selected to evaluate the influence of counter-cations and ligands on de-excitation mechanisms responsible for multicomponent emission of cluster units. This study evaluates the ageing of each member of the series, which is crucial for further energy conversion applications (photovoltaic, lighting, water splitting, etc.).

Effects of the nature of substrates, either crystalline or non-crystalline, on the structure and properties of ZnO films deposited by sputtering were investigated. This study focuses mainly on the role of the external electric bias applied to substrates during magnetron sputtering deposition in controlling crystalline polarity, i.e., Zn-face or O-face, and the resulting film properties. It was found that polarity control was achieved on silica and silicon substrates but not on sapphire substrates. The substrate bias did influence the lattice parameters in the structural formation; however, the selection of the substrate type had a significant influence on the defect structures and the film properties.

Synthesizing pure phase Ba3Si6O9N4 by the conventional solid-state reaction method is challenging because of easily formed secondary phase Ba3Si6O12N2 showing similar crystal structure. In this work, an alternative low temperature synthesis method is presented, and a series of green to blue emitting (Ba, Sr)3Si6O9N4: Eu2+ phosphors were prepared by a mechanochemical activation route. Variations in photoluminescence properties and crystal structure, as induced by the change in phosphor composition, were investigated. Under ultraviolet-light excitation, Ba3Si6O9N4: Eu2+ phosphor exhibited a strong narrow green emission at 518 nm and simultaneously a weak emission at 405 nm, which are ascribed to different Eu/Ba sites in Ba3Si6O9N4 lattice proved by Density Functional Theory (DFT) calculations. A continuous green to blue emission in (Ba, Sr)3Si6O9N4: Eu2+ phosphors could be achieved by tuning the crystal structure and local coordination environment acting on Eu2+ with Sr/Ba substitution. More Sr/Ba substitution improved thermal quenching and resulted in a different characteristic of emission peak shift upon increasing the temperature.

(GaN)1-x(ZnO)x solid-solution nanostructures with superior crystallinity, large surface areas and visible light absorption have been regarded as promising photocatalysts for overall water splitting to produce H2. In this work, we report the preparation of (GaN)1-x(ZnO)x solid-solution nanorods with a high ZnO solubility up to 95% via a two-step synthetic route, which starts from a sol-gel reaction and follows with a nitridation process. Moreover, we clearly demonstrated that the crystallographic facets of (GaN)1-x(ZnO)x solid-solution nanorods can be finely tailored from non-polar {10̄10} to semipolar {10̄11} and then finally to mixed {10̄1} and polar {000̄1} by carefully controlling the growth temperature and nitridation time. Correspondingly, the ZnO content in the GaN lattice can be achieved in the range of ∼25%-95%. Room-temperature cathodoluminescence (CL) measurements on the three types of (GaN)1-x(ZnO)x solid-solution nanorods indicate that the minimum band-gap of 2.46 eV of the solid-solution nanorods is achieved under a ZnO solubility of 25%. The efficiency and versatility of our strategy in the band-gap and facet engineering of (GaN)1-x(ZnO)x solid-solution nanorods will enhance their promising photocatalytic utilizations like an overall water splitting for H2 production under visible-light irradiation.

Nanoscale semiconductor heterostructures with superior crystal quality, large surface area and designed interfaces provide more opportunities for building high-performance optoelectronic nanodevices and harvesting clean energy. In this work, we report the rational synthesis of In2S3/In2O3 heterostructures through a two-channel chemical vapor deposition (CVD) process. The In2S3/In2O3 heterostructures feature a bundle-like morphology with In2S3 nanowires covering randomly distributed In2O3 nanoparticles. High-resolution transmission electron microscopy (HRTEM) analysis on the In2S3/In2O3 heterostructures finds that both In2S3 nanowires and In2O3 nanoparticles show a crystalline nature, but the lattice matching between the two crystal domains is not observed at the interface, implying that the heterostructure is formed via a simple physical adsorption. Cathodoluminescence (CL) studies on In2S3/In2O3 heterostructures indicate that the as-synthesized heterostructures have a broad emission in the range of 400–950 nm, covering the whole visible light spectrum from violet to infrared. Finally, the formation process of In2S3/In2O3 heterostructures and their optical emission behaviors are discussed based on detailed structural analyses.

International audience; This review paper summarizes our very recent works on the synthesis of multifunctional transparent nanocomposite thin films or coatings based on metal atom clusters by an electro-phoretic deposition (EPD) process. Eight different octahedral atom clusters with niobium, molybdenum or tantalum as metallic cores were used to prepare highly transparent thin films in the visible. Green, yellow, orange, red and brown colored films were successfully fabricated by coating on a transparent conductive oxide glass substrate. Transparent nanocomposite films with prominent luminescent properties were obtained by using Mo 6 clusters whereas ultraviolet (UV) and near infrared (NIR) filters were realized by using Nb 6 or Ta 6 clusters. The EPD process appears to be a new strategy to fabricate highly transparent , homogeneous and colored nanocomposite thin films and coatings for smart windows and solar technologies in a very short time (

Beta-sialon:Eu2+ phosphor deposits were fabricated by electrophoretic deposition (EPD) process within a strong magnetic field (12 T). The direction of the magnetic field was adjusted to be parallel or perpendicular to that of the electric field, that is, vertical-or horizontal setup. The oriented deposits were fabricated by aligning the β-sialon:Eu2+ particles along the higher magnetic-susceptibility c-crystal axis (a, b-crystal plane). For the case of vertically-setup magnetic field, the oriented deposit aligned along the c-axis possessed higher relative deposit density than the randomly fabricated deposit, as a result, varying the intensity ratio of emission and transmitted excitation, and therefore, presenting different chromaticity coordinates; for the case of horizontally-setup magnetic field, photoluminescence (PL) intensities of the deposits oriented along c-axis were significantly improved by comparing with those of the randomly-oriented ones.

Cathodoluminescence spectra of Ca codoped (La,Ce)Al(Si6−zAlz)(N10−zOz) (z~1) (termed JEM phase) phosphors were analyzed microscopically. The as-prepared samples consisted of a major JEM phase and a small amount of β-sialon and/or α-sialon depending on the Ca concentration. A microscale distribution of three different emission spectra was clearly observed on one phosphor particle, which was originated from the blue-emitting JEM:Ce (430 nm), β-sialon:Ce (435 nm) and Ca-α-sialon:Ce (475 nm), respectively. The volume ratio of the three phases thus led to changes in the bandwidth and the maximum position of the emission spectrum, and the redshift of CL spectra with increasing Ca concentration was dominantly attributed to the enhanced emission from Ca-α-sialon. The microanalysis of phosphor particles with the aid of cathodoluminescence spectroscopy indicated a similar result of the phase assembly that was identified by the powder X-ray diffraction.

Knowing the physicochemical properties of a material is of great importance to design and utilize it in a suitable way. In this paper, we conduct a comprehensive survey of photoluminescence spectra, localized cathodoluminescence, temperature-dependent luminescence efficiency, and applications of Eu(2+)-doped Sr0.5Ba0.5Si2O2N2 in solid-state lighting. This phosphor exhibits a broad emission band with a maximum at 560-580 nm and a full-width at half maximum of 92-103 nm upon blue light excitation, whereas a dual-band emission (i.e., 470 nm and 550 nm) is observed under electron beam irradiation due to perhaps the intergrowth of BaSi2O2N2:Eu(2+) and Sr0.5+σBa0.5-σSi2O2N2:Eu(2+) in each phosphor particle. Under 450 nm blue light irradiation, this yellow phosphor exhibits excellent luminescence properties with absorption, internal and external efficiencies of 83.2, 87.7 and 72.6%, respectively. Furthermore, it also possesses high thermal stability, with the quantum efficiency being decreased by only 4.2% at 150 °C and a high quenching temperature of 450 °C. High-efficiency white LEDs using the title phosphor have a luminous efficacy, color temperature and color rendition of ∼120 lm W(-1), 6000 K and 61, respectively, validating its suitability for use in solid-state white lighting.

To modify the luminescence properties of Ce3+-doped Y3Al5O12 (YAG) phosphors, they have been coated with a carbon layer by chemical vapor deposition and subsequently heat-treated at high temperature under N2 atmosphere. Luminescence of the carbon coated YAG:Ce3+ phosphors has been investigated as a function of heat-treatment at 1500 and 1650 °C. The 540 nm emission intensity of C@YAG:Ce3+ is the highest when heated at 1650 °C, while a blue emission at 400-420 nm is observed when heated at 1500 °C but not at 1650 °C. It is verified by X-ray diffraction (XRD) that the intriguing luminescence changes are induced by the formation of new phases in C@YAG:Ce3+-1500 °C, which disappear in C@YAG:Ce3+-1650 °C. In order to understand the mechanisms responsible for the enhancement of YAG:Ce3+ emission and the presence of the blue emission observed for C@YAG:Ce3+ -1500 °C, the samples have been investigated by a combination of several electron microscopy techniques, such as HRTEM, SEM-CL, and SEM-EDS. This local and cross-sectional analysis clearly reveals a gradual transformation of phase and morphology in heated C@YAG:Ce3+ phosphors, which is related to a reaction between C and YAG:Ce3+ in N2 atmosphere. Through reaction between the carbon layer and YAG host materials, the emission colour of the phosphors can be modified from yellow, white, and then back to yellow under UV excitation as a function of heat-treatment in N2 atmosphere.

We report the photoluminescence (PL) and cathodoluminescence (CL) properties of face-capped [Mo6Xi 8La 6]2− (X = Cl, Br, I; L = organic or inorganic ligands) cluster units. We show that the emission of Mo6 metal atom clusters depends not only on the nature of X and L ligands bound to the cluster and counter-cations, but also on the excitation source. Seven members of the AxMo6Xi 8La 6 series (A = Cs+, (n-C4H9)4N+, NH4 +) were selected to evaluate the influence of counter-cations and ligands on de-excitation mechanisms responsible for multicomponent emission of cluster units. This study evaluates the ageing of each member of the series, which is crucial for further energy conversion applications (photovoltaic, lighting, water splitting, etc.).

International audience; Among the solution deposition techniques, electrophoretic deposition (EPD) is a fairly rapid and low cost two-step process well-known for ceramic shaping and conductive surface coating. Recently we have reported the fabrication of transparent inorganic thin film composed of octahedral molybdenum clusters and shown that the stabilization of the cluster solutions during EPD is very important to obtain high quality films. In this study, we selected the Cs2Mo6Br i 8Br a 6 or ((n-C4H9)4N)2Mo6Br i 8Br a 6 clusters compound (i = inner ligands, a = apical ligands) as precursors in a Methyl Ethyl Ketone (MEK) solution to fabricate the inorganic Mo6 cluster transparent film on a conductive indium tin oxide (ITO) glass substrate. For the first time, the mechanism for the deposition process of metal clusters is proposed based on results obtained by the combination of complementary techniques such as infrared spectroscopy, X-ray analysis and electron microscopy. The Mo6 film on the ITO glass substrate exhibiting a Br-rich layer is quickly deposited during the first stage of the EPD followed by a multilayer structure consisting of two types of cluster compounds, [Mo6Br i 8Br a 4(H2O) a 2] and (H3O)2[Mo6Br i 8Br a 4(OH) a 2].

International audience; This study reports the first integration of inorganic tantalum octahedral metal atom clusters into multifunctional nanocomposite coating materials and devices for window technology and energy saving applications. [Ta6Br12i](n+) (n = 2, 3 or 4) cluster-based high visible transparency UV and NIR filters are realized. Green and brown colored films are fabricated by coating on an indium-doped tin oxide glass substrate by electrophoretic deposition, an industrialized solution process. The efficiency in energy saving of the new UV-NIR filters was estimated by the determination of different figure of merit (FOM) values, such as Tvis, Tsol and Tvis/Tsol (Tsol = solar transmittance and Tvis = visible transmittance), and the color coordinates (x, y, z and L*a*b). The Tvis/Tsol ratio is equal to 1.25 for the best films. Such values are evidence of a higher energy saving efficiency than most of the inorganic composites reported in the literature. These promising results pave the way for the use of transition metal clusters as a new class of nanocoatings in energy saving window-based applications.

Sb/P co-doped Gallium Nitride (GaN) nanowires were synthesized via a simple chemical vapor deposition (CVD) process by heating Ga2O3 and Sb powders in NH3 atmosphere. Scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDS) measurements confirmed the as-synthesized products were Sb/P co-doped GaN nanowires with rough morphology and hexagonal wurtzite structure. Room temperature cathodoluminescence (CL) demonstrated that an obvious band shift of GaN nanowires can be observed due to Sb/P co-doping. Possible explanation for the growth and luminescence mechanism of Sb/P co-doped GaN nanowires was discussed.

Multiple stacked InGaN/GaN quantum dots are embedded into an InGaN p-n junction to develop multilevel intermediateband (MIB) solar cells. An IB transition is evidenced from both experiment and theoretical calculations. The MIB solar cell shows a wide photovoltaic response from the UV to the near-IR region. This work opens up an interesting opportunity for high-efficiency IB solar cells in the photovoltaics field.

Blue-emitting Sr1−xEuxSi9Al19ON31 phosphors were synthesized at 1800 °C for 2 h under 1 MPa N2 by using the gas-pressure sintering method (GPS). The microstructure, photoluminescence (PL) properties of the prepared phosphors were investigated. Under the 290 nm excitation, broad PL emission bands with peak positions at 448–490 nm were detected. The concentration quenching was not observed owing to the large distance betweenEu2+ ions that made the nonradiative energy transfer between neighboring Eu2+ ions difficult. The blue phosphor generally showed a small thermal quenching at low Eu2+ concentrations. The absorption and external quantum efficiency of the synthesized Sr0.5Eu0.5Si9Al19ON31 were 85% and 62% upon the 365 nm excitation, respectively. The interesting PL results indicate that Sr1−xEuxSi9Al19ON31 has great potentials as a blue phosphor for white LEDs applications.

Spatially and spectrally resolved cathodoluminescence (CL) is one of the most effective methods to explore the optical properties of a nanomaterials and reveals the spatial distribution as well as the correlation between the luminescence and the sample morphology and microstructure. Here, CL modulation of ZnS nanostructures by controlled morphologies, Fe/Mn doping, and measurement temperature is demonstrated. High quality ZnS nanobelts and nanorods are synthesized on an Au-coated Si substrate and an Au-coated GaAs substrate via a facile thermal evaporation route. A room-temperature sharp ultraviolet (UV) lasing-like peak in various ZnS is achieved. The main UV luminescence peaks appear at wavelengths between 330 and 338 nm. The low temperature (32 K) CL spectrum consists of a narrow and strong UV peak centered at 330 nm and two broad, low-intensity peaks in the visible region (514 and 610 nm). Temperature-dependent CL from such single-crystalline ZnS nanobelts in the temperature range of 32 to 296 K reveals two UV peaks at 3.757 and 3.646 eV. The effects of Fe doping and Fe/Mn co-doping on the CL property of ZnS nanobelts are further investigated. These results imply that ZnS nanostructures can be used for potential luminescent materials as well as short-wavelength nanolaser light sources.

Formation of cadmium oxide microcrystals, induced by Ar ion irradiation, on CdTe crystals is reported. The formation of the oxide crystallites is proved by the detection of a low temperature cathodoluminescence emission, centered at 2.2 eV. The emission is localized at the microcrystals on the irradiated CdTe surfaces. The compositional changes, after the irradiation, are studied by Energy Dispersive X-Ray spectroscopy and X-Ray Diffraction. The concurrent decrease of the near band edge CdTe luminescence emission and the increase of the 2.2 eV band intensity are correlated to the irradiation fluence. (C) 2012 Elsevier B.V. All rights reserved.

Influence of the growth temperature on the luminescence properties of Eu,Si-codoped AlN was studied by means of SEM, XRD and CL. The Si and Eu concentrations were fixed at 2.2 and 0.1 at%, respectively, while the growth temperature was varied from 1600 to 1950◦C. The synthesized Eu,Si-doped AlN powders emit in the ultraviolet range, with bands at 350 and 380 nm, and in the visible range, with bands at 460 and 560 nm. An increase of the 460 nm emission is observed with the temperature increase, while the 560 nm emission disappears above 1700◦C. On the other hand, the luminescence distribution is strongly affected by the temperature. The luminescence variation is discussed in terms of dopants diffusion inside AlN grains. © 2013 The Electrochemical Society. [DOI: 10.1149/2.012307jss] All rights reserved.

International audience; Bioimaging and cell labeling using red or near infrared phosphors emitting in the ''therapeutic window'' of biological tissues have recently become some of the most active research fields in modern medical diagnostics. However, because organic and inorganic autofluorophores are omnipresent in nature, very often the background signal from fluorochromes other than targeted probes has to be eliminated. This discrimination could be available using a time-gated luminescence microscopy (TGLM) technique associated with long lifetime phosphorescent nanocomposites. Here, we report new SiO2 nanostructured particle (50 nm in diameter) embedded luminescent nanosized [Mo6I8(C2F5COO)(6)](2-) metal atom clusters (1 nm in diameter), successfully prepared by the microemulsion technique. This combination provides new physical insight and displays red emission in biological based solution under UV-Vis excitation with long lifetimes of around 17 and 84 mu s. Moreover, the nanoparticles can be internalized by cancer cells after surface functionalization by transferrin protein and clearly imaged by TGLM under excitation at 365 nm. The nanocomposites have been mainly characterized by scanning and transmission electron microscopies (SEM and HAADF-STEM), UV-Vis and photoluminescence (PL) spectroscopies.

Nitride and oxynitride (Sialon) phosphors are good candidates for the ultraviolet and visible emission applications. High performance, good stability and flexibility of their emission properties can be achieved by controlling their composition and dopants. However, a lot of work is still required to improve their properties and to reduce the production cost. A possible approach is to correlate the luminescence properties of the Sialon particles with their local structural and chemical environment in order to optimize their growth parameters and find novel phosphors. For such a purpose, the low-voltage cathodoluminescence (CL) microscopy is a powerful technique. The use of electron as an excitation source allows detecting most of the luminescence centers, revealing their luminescence distribution spatially and in depth, directly comparing CL results with the other electron-based techniques, and investigating the stability of their luminescence properties under stress. Such advantages for phosphors characterization will be highlighted through examples of investigation on several Sialon phosphors by low-energy CL.

Bioimaging and cell labeling using red or near infrared phosphors emitting in the "therapeutic window" of biological tissues have recently become some of the most active research fields in modern medical diagnostics. However, because organic and inorganic autofluorophores are omnipresent in nature, very often the background signal from fluorochromes other than targeted probes has to be eliminated. This discrimination could be available using a time-gated luminescence microscopy (TGLM) technique associated with long lifetime phosphorescent nanocomposites. Here, we report new SiO

The development of phosphor devices free of heavy metal or rare earth elements is an important issue for environmental reasons and energy efficiency. Different mixtures of ZnO nanocrystals with Cs2Mo6I8(OOC2F5)6 cluster compound (CMIF) dispersed into polyvinylpyrrolidone matrix have been prepared by very simple and low cost solution chemistry. The resulting solutions have been used to fabricate highly transparent and luminescent films by dip coating free of heavy metal or rare earth elements. The luminescence properties of solution and dip-coated films were investigated. The luminescence of such a system is strongly dependent on the ratios between ZnO and CMIF amounts, the excitation wavelength and the nature of the system. By varying these two parameters (ratio and wavelength), a large variety of colors, from blue to red as well as white, can be achieved. In addition, differences in the luminescence properties have been observed between solutions and thin films as well as changes of CMIF emission band maximum wavelength. This may suggest some possible interactions between the different luminophore centers, such as energy transfer or ligands exchange on the Mo6 clusters., Graphical Abstract

International audience; Nitrogen doped zinc oxide (ZnO) nanoparticles have been synthesized using a colloidal route and low temperature nitridation process. Based on these results, 200 nm thick transparent ZnO thin films have been prepared by dip-coating on SiO2 substrate from a ZnO colloidal solution. Zinc peroxide (ZnO2) thin film was then obtained after the chemical conversion of a ZnO colloidal thin film by H2O2 solution. Finally, a nitrogen doped ZnO nanocrystalline thin film (ZnO:N) was obtained by ammonolysis at 250°C. All the films have been characterized by scanning electron microscopy, X-ray diffraction, X-Ray photoelectron spectroscopy and UV-Visible transmittance spectroscopy.

International audience; Thin films of octahedral molybdenum metal clusters (Mo6) were fabricated on indium tin oxide (ITO) glass slides by the electrophoretic deposition (EPD) technique. The solubility of the Cs2Mo6Br14 cluster compounds, which are composed of [Mo6Bri8Bra6]2− units associated with two cesium cations, in different solvents was investigated in order to achieve a well-dispersed colloidal solution of the Mo6 cluster units that was stable during the following EPD process. Distilled water, ethanol, 1-propanol, acetone, methyl-ethyl ketone (MEK) and acetyl acetone were selected as the dispersing media of the Cs2Mo6Br14 cluster compounds. Homogeneous, transparent Mo6 cluster films with prominent luminescent properties were obtained by the EPD when dissolving Cs2Mo6Br14 into the MEK and acetyl acetone solutions. The obtained Mo6 cluster films were examined by investigating the thickness (color 3D laser spectroscopy), the morphology (FE-SEM), the Br/Mo ratio (XRF), and the crystallographic parameters variation (XRD). The optical emission properties were characterized by UV-Vis spectroscopy, FL spectroscopy and micro PL spectroscopy. The thickness of the Mo6 cluster films changed depending on the kind of the solvents. The atomic ratio of the Mo and Br elements in the Mo6 cluster-based unit were relatively maintained during the dispersion and deposition in the MEK solution. The UV-Vis absorption spectra exhibited a high transparency in the visible light range (500 – 850 nm) accompanied by many peaks due to light interference in the wavelength range from 400 nm to 2000 nm. The emission intensity of the Mo6 cluster film deposited in MEK slightly decreased during continuous irradiation of 325 nm laser light for 600s.

In this work we report the enhancement of the 3C-SiC band edge luminescence induced by the SiO2 shell in SiC/SiO2 core/shell nanowires (NWs) system. We demonstrate that the shell enhances the SiC near band edge luminescence and we argue the formation of a type-I quantum well between the SiC core and the SiO2 shell, with the consequent injection of carriers from the larger band-gap shell to the narrower band-gap core.

article i nfo The luminescence properties of SiC/SiO2 core/shell nanowires with different core to shell thickness ratio are analysed by SEM-Cathodoluminescence spectroscopy. The different radial NW structure, studied by trans- mission electron microscopy, deeply influences the efficiency of competitive radiative transitions. As the core to shell ratio decreases, the increase of a UV emission component is observed indicating that the elec- tron-hole pairs recombine directly in the silicon dioxide and the beneficial effect of shell-induced enhance- ment of the core emissions is less efficient.

This study focus on the nature of different Si-based sensitizers for Er3+ions in Silicon- Rich Silicon oxide thin films. The samples were first analyzed by Cathodoluminescence technique to probe all emitting centers in the films. Some of these centers were found to be potential sensitizers for Er3+ions, such as Silicon Oxygen Deficient Center and Non-Bridging Oxygen Hole Center, in addition to the well-known Silicon-nanoclusters (Si-nc). The influence of the thickness was subsequently examined, revealing that the formation of Si-nc is inhibited for films thinner than 100 nm and this led to less sensitization of the Er3+ions. We demonstrate that the introduction of a SiO2buffer layer can overcome this issue and increase the luminescence of Er3+ions by a factor of five for films thinner than 50 nm that are usually used for electrically-driven photonic devices.

Luminescence properties of individual BN-coated CaS:Eu nanowires have been studied by high-spatial-resolution cathodoluminescence (CL) spectroscopy. A broad red light-emitting band from an individual nanowire has been observed. Detailed local CL studies on the nanowires reveal spatial variations of luminescence from the structure surfaces toward their cores. Such variations are attributed to the different Eu2+ ions surroundings within the surface and core nanowire regions. The attractive luminescence properties are meaningful for fundamental studies of nanoscaled luminescent materials and may be of interest for novel optoelectronic applications.

Since the discovery of carbon nanotubes (CNTs) in 1991, widespread research has been carried out to understand their useful physical and electronic properties and also to explore their use in devices. CNTs have many unique properties such as tunable electrical resistance, mechanical robustness, and high thermal conductivity, which when combined with other inorganic materials such as phosphors or superconductors could lead to hetero-structures with diverse functionality. We have been able to obtain mass production of such materials wherein CNTs form core-shell heterostructures with metals, semiconductors, insulators, and even metal-semiconductor heterojunctions. The emerging strategy employs a high-temperature chemical vapor deposition (CVD) technique and high heating rates. Interestingly, due to their high temperature stability, CNTs can act as a nanoreactor for production of exotic materials inside it. In this article, we take ZnS-filled CNTs as an example to explain our synthesis strategy. We explore the optical behavior of these complex materials, analyzing both their luminescence and degradation upon exposure to an electron beam. In addition, the mechanical response of filled CNTs has been evaluated individually inside a transmission electron microscope fitted with an atomic force microscopy–transmission electron microscopy (AFM–TEM) sample holder. Many applications can be envisioned for these nanostructures ranging from nanothermometers to photo-protective storage and delivery devices.

The effects of chemical treatment on the luminescence of ZnO were investigated by cathodoluminescence. For this purpose, ZnO ceramics and O- and Zn-terminated faces of ZnO single crystals were studied. The samples were dipped in KOH and HCl solutions as well as pure H 2 O for 3 min. H 2 O and HCl treatments of ZnO ceramics can increase or decrease the initial ultraviolet (UV) intensity depending on the location examined, and induce an increase of the UV intensity under e-beam irradiation. HCl treatment of the Zn-face of ZnO single crystals slightly affects the surface morphology and the luminescence. HCl treatment of the O-face etches the surface to hexagonal pyramidal features. In addition, the initial UV intensity is always lower for the HCl-treated than for the untreated O-face, while the UV intensity increases at the beginning of e-beam irradiation. These results suggest that the UV intensity is influenced by the surface and bulk reactions of H + with ZnO.

The synthesis of the (rocksalt phase) single-crystal square-like cross-sectional MgS nanotubes via a thermal reaction process was reported for the first time in the family of II–VI sulfide semiconductors, which enriches the wide spectrum of diverse inorganic nanotubular structures. As-grown MgS nanotubes are structurally uniform single-crystals; an individual faceted tube is enclosed by four {020} crystal planes and grows along the [001] orientation. The MgS nanotubes exhibited efficient hydrogen-storage capacity of ∼ 2.2 wt% at room temperature under hydrogen pressure of 33.6 atm and one intensive cathodoluminescence emission band centered at ∼ 688 nm. The new concept established here will be very helpful in developing other types of Mg-based material nanotubes with high a hydrogen-storage capacity. Moreover, the MgS nanotubes' cavity could be filled with different semiconducting materials with various band gaps to give interesting electrical and optical nanodevices.

Eu 2+ -doped AlN-polytypoids (8H, 15R, 12H, and 21R) were successfully synthesized by nitrogen-gas-pressure sintering. The phosphors show intense blue emissions under the electron beam excitation. All the polytypoid phosphors exhibit relatively a smaller degradation in luminance and a higher thermal stability in comparison to the oxide counterparts. Among the polytypoids, 12H has no luminance saturation, and shows a brightness of 40 cd/m 2 at 3 kV and 100 lA. These results indicate that Eu 2+ -doped AlN-polytypoids could also be used as blue phosphors for FEDs.

High-quality, uniform one-dimensional Cds micro/nanostructures with different morphologies-microrods, sub-microwires and nanotips-are fabricated through an easy and effective thermal evaporation process. Their structural, cathodoluminescence and field-emission properties are systematically investigated. Microrods and nanotips exhibit sharp near-band-edge emission and broad deep-level emission, whereas sub-microwires show only the deep-level emission. A significant decrease in a deep-level/near-band-edge intensity ratio is observed along a tapered nanotip towards a smaller diameter part. This behaviour is understood by consideration of defect concentrations in the nanotips, as analyzed with high-resolution transmission electron microscopy. Field-emission measurements show that the nanotips possess the best field-emission characteristics among all 1D Cds nanostructures reported to date, with a relatively low turn-on field of 5.28 V mu m(-1) and the highest field-enhancement factor of 48.19. The field-enhancement factor, turn-on and threshold fields are discussed related to structure morphology and vacuum gap variations under emission.

The luminescence properties of Si,Eu-codoped AlN phosphors were investigated by means of cathodoluminescence. The concentration of Eu was kept constant, while that of Si was varied from 0 to 9.0 at.% using two different Si-source starting powders, Si3N4 and SiC. The luminescence of Eu2+ in AlN is only observed for samples doped with Si. On the other hand, a concentration quenching is observed for samples doped with high amount of Si from Si3N4 while not for those doped from SiC. These results show the importance of Si in the luminescence properties of Eu2+-doped AlN.

[*] Dr. X. S. Fang, Prof. Y. Bando, Dr. U. K. Gautam, Dr. C. Y. Zhi, Dr. B. D. Liu, Dr. T. Y. Zhai, Prof. D. Golberg International Center for Young Scientists (ICYS) and World Premier International Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) Namiki 1-1, Tsukuba, Ibaraki 305-0044 (Japan) E-mail: fang.xiaosheng@nims.go.jp; xshfang@yahoo.cn Dr. M. Y. Liao, Prof. Y. Koide Sensor Materials Center, NIMS Namiki 1-1, Tsukuba, Ibaraki 305-0044 (Japan)

The effects of the low-energy electron beam on ZnO single crystals were investigated by cathodoluminescence (CL), Time-of-Flight Electron Stimulated Desorption (TOF-ESD) and Temperature Programmed Desorption (TPD). Under e-beam irradiation, the ultraviolet (UV) emission decreases exponentially for O-face, while it increases and then decreases for Zn-face. Meanwhile, a large desorption of H+ is observed by TOF-ESD for both O- and Zn-faces. On the other hand, an increase of H in the irradiated volume is observed after stopping the e-beam irradiation. Similar H2 desorption is found by TPD for both faces. These data suggest that the decrease of the UV intensity is related to H desorption.

Homogenous crystallization in solution, in the absence of external influences, is expected to lead to growth that is symmetric at least in two opposite facets. Such was not the case when we attempted to synthesize ZnO nanostructures by employing a solvothermal technique. The reaction product, instead, consisted of bullet-shaped tiny single crystals with an abrupt hexagonal base and a sharp tip. A careful analysis of the product and the intermediate states of the synthesis reveals that one of the reaction intermediates with sheet-like morphology acts as a self-sacrificing template and induces such unexpected and novel growth. The synthesis was further extended to dope the nanobullets with nitrogen as previous studies showed this can induce p-type behavior in ZnO, which is technologically complementary to the naturally occurring n-type ZnO. Herein, a soft-chemical approach is used for the first time for this purpose, which is otherwise accomplished with high-temperature techniques. Cathodoluminesce (CL) investigations reveal stable optical behavior within a pure nanobullet. On the other hand, the CL spectra derived from the surfaces and the cores of the doped samples are different, pointing at a N-rich core. Finally, even though N-doped ZnO is known to have high electrical conductivity, the study now demonstrates that the field-emission properties of ZnO can also be greatly enhanced by means of N doping.

We report on a controlled synthesis of two novel semiconducting heterostructures: heterocrystalline-ZnS/single-crystalline-ZnO biaxial nanobelts and side-to-side single-crystalline ZnS/ZnO biaxial nanobelts via a simple one-step thermal evaporation method. In the first heterostructure, a ZnS domain is composed of the heterocrystalline superlattice (3C-ZnS) N /(2H-ZnS) M [111]-[0001] with the atomically smooth interface between wurtzite and zinc blende ZnS fragments. High-spatial resolution cathodoluminescence studies on individual heterostructures for the first time reveal a new ultraviolet emission peak ( approximately 355 nm), which is not observed in separate ZnS or ZnO nanostructures. The present hererostructures are expected to become valuable not only with respect to fundamental research but also for a design of new broad-range ultraviolet nanoscale lasers and sensors.