Transition of Emission Colours as a Consequence of Heat-Treatment of Carbon Coated Ce-Doped YAG Phosphors.

To modify the luminescence properties of Ce-doped Y₃Al₅O (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:Ce phosphors has been investigated as a function of heat-treatment at 1500 and 1650 °C. The 540 nm emission intensity of C@YAG:Ce 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.

Mo cluster-based compounds for energy conversion applications: comparative study of photoluminescence and cathodoluminescence.

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.

Low-energy Cathodoluminescence for (Oxy)Nitride Phosphors.

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.

Visible tunable lighting system based on polymer composites embedding ZnO and metallic clusters: from colloids to thin films.

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 CsMoI(OOCF) 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.

Time-gated luminescence bioimaging with new luminescent nanocolloids based on [MoI(CFCOO)] metal atom clusters.

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.

Solubility and crystallographic facet tailoring of (GaN)(1-x)(ZnO)(x) pseudobinary solid-solution nanostructures as promising photocatalysts.

(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.

Europium(ii)-activated oxonitridosilicate yellow phosphor with excellent quantum efficiency and thermal stability - a robust spectral conversion material for highly efficient and reliable white LEDs.

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.

Strong Energy-Transfer-Induced Enhancement of Luminescence Efficiency of Eu(2+)- and Mn(2+)-Codoped Gamma-AlON for Near-UV-LED-Pumped Solid State Lighting.

A series of Eu(2+)- and Mn(2+)-codoped γ-AlON (Al1.7O2.1N0.

Local defect-induced red-shift of cathodoluminescence in individual ZnS nanobelts.

The luminescence of semiconductor nanostructures is strongly dependent on their size, dimensions, morphology, composition, or defects, and their band emissions can be properly and selectively tailored through the rational manipulation of these parameters during material growth. Using spatially-resolved cathodoluminescence spectroscopy, monochromatic contrast maps and high-resolution transmission electron microscopy, an obvious red-shift of the near-band-edge emission of wurtzite ZnS nanobelts, resulting from a strip of stacking faults or a zinc-blende phase with tens of atomic layers in width, has been observed and its related mechanism has been discussed. This finding is not specific to the defect-dependent optical properties tailoring of ZnS nanostructures and represents a general validity for clarifying the mechanism of peak-shift (band-gap expansion or shrinking) of a wide range of semiconductor nanostructures with various defects.

Origin of yellow-band emission in epitaxially grown GaN nanowire arrays.

Here, we report the origin of the yellow-band emission in epitaxial GaN nanowire arrays grown under carbon-free conditions. GaN nanowires directly grown on [0001]-oriented sapphire substrate exhibit an obvious and broad yellow-band in the visible range 400-800 nm, whereas the insertion of Al/Au layers in GaN-sapphire interface significantly depresses the visible emission, and only a sharp peak in the UV range (369 nm) can be observed. The persuasive differences in cathodoluminescence provide direct evidence for demonstrating that the origin of the yellow-band emission in GaN nanowire arrays arises from dislocation threading.

Zn vacancy induced green luminescence on non-polar surfaces in ZnO nanostructures.

Although generally ascribed to the presence of defects, an ultimate assignment of the different contributions to the emission spectrum in terms of surface states and deep levels in ZnO nanostructures is still lacking. In this work we unambiguously give first evidence that zinc vacancies at the (1010) nonpolar surfaces are responsible for the green luminescence of ZnO nanostructures. The result is obtained by performing an exhaustive comparison between spatially resolved cathodoluminescence spectroscopy and imaging and ab initio simulations.

A novel and high brightness AlN:Mn2+ red phosphor for field emission displays.

Mn(2+) doped-AlN red phosphors were prepared by the solid-state reaction method. X-ray diffraction, SEM-EDS, photoluminescence and cathodoluminescence were utilized to characterize the prepared phosphor. Under UV light or electron beam excitation, the AlN:Mn(2+) phosphors exhibit a strong red emission centered at 600 nm, which is ascribed to the characteristic (4)T1((4)G)-(6)A1((6)S) transition of Mn(2+).

A multilevel intermediate-band solar cell by InGaN/GaN quantum dots with a strain-modulated structure.

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.

Local analysis of Eu emission in CaAlSiN.

We have investigated the local luminescence properties of Eu-doped CaAlSiN by using low-energy electron beam (e-beam) techniques. The particles yield broad emission centered at 655 nm with a shoulder at higher wavelength under light excitation, and a broad band around 643 nm with a tail at 540 nm under e-beam excitation. Using cathodoluminescence (CL) in a scanning electron microscope (SEM), we have observed small and large particles, which, although with different compositions, exhibit Eu-related emissions at 645 and 635 nm, respectively.

Synthesis, microstructure, and cathodoluminescence of [0001]-oriented GaN nanorods grown on conductive graphite substrate.

One-dimensional GaN nanorods with corrugated morphology have been synthesized on graphite substrate without the assistance of any metal catalyst through a feasible thermal evaporation process. The morphologies and microstructures of GaN nanorods were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results from HRTEM analysis indicate that the GaN nanorods are well-crystallized and exhibit a preferential orientation along the [0001] direction with Ga(3+)-terminated (101̅1) and N(3-)-terminated (101̅1̅) as side facets, finally leading to the corrugated morphology surface.

Solid solution, phase separation, and cathodoluminescence of GaP-ZnS nanostructures.

Quaternary solid-solution nanowires made of GaP and ZnS have been synthesized through well-designed synthetic routines. The as-synthesized GaP-ZnS solid-solution nanowires exhibit decent crystallinity with the GaP phase as the host, while a large amount of twin structural defects are observed in ZnS-rich nanowires. Cathodoluminescence studies showed that GaP-rich solid-solution nanowires have a strong visible emission centered at 600 nm and the ZnS-rich solid-solution nanowires exhibited a weak emission peak in the UV range and a broad band in the range 400-600 nm.

Triangular ZnO nanosheets: synthesis, crystallography and cathodoluminescence.

ZnO nanosheets with triangular morphology have been synthesized on an Au-coated silicon substrate through a facile thermal evaporation process. The morphologies and microstructures of the nanosheets were studied by a scanning electron microscope (SEM) and a high-resolution transmission electron microscope (HR-TEM). These studies show that a nanosheet is commonly composed of two parts: a triangular ZnO sheet and an Au nanoparticle attached on its tip-end.

Bulk synthesis, growth mechanism and properties of highly pure ultrafine boron nitride nanotubes with diameters of sub-10 nm.

As a structural analogue of the carbon nanotube (CNT), the boron nitride nanotube (BNNT) has become one of the most intriguing non-carbon nanostructures. However, up to now the pre-existing restrictions/limitations of BNNT syntheses have made the progress in their research rather modest. This work presents a new route toward the synthesis of highly pure ultrafine BNNTs based on a modified boron oxide (BO) CVD method.

Spatially resolved cathodoluminescence of individual BN-coated CaS:Eu nanowires.

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.

Low-energy cathodoluminescence microscopy for the characterization of nanostructures.

Spatially and spectrally resolved low-energy cathodoluminescence (CL) microscopy was applied to the characterization of nanostructures. CL has the advantage of revealing not only the presence of luminescence centers but also their spatial distribution. The use of electrons as an excitation source allows a direct comparison with other electron-beam techniques.

Enhancement of the core near-band-edge emission induced by an amorphous shell in coaxial one-dimensional nanostructure: the case of SiC/SiO2 core/shell self-organized nanowires.

We report the influence of the native amorphous SiO(2) shell on the cathodoluminescence emission of 3C-SiC/SiO(2) core/shell nanowires. A shell-induced enhancement of the SiC near-band-edge emission is observed and studied as a function of the silicon dioxide thickness. Since the diameter of the investigated SiC cores rules out any direct bandgap optical transitions due to confinement effects, this enhancement is ascribed to a carrier diffusion from the shell to the core, promoted by the alignment of the SiO(2) and SiC bands in a type I quantum well.

Effect of Size-Dependent Thermal Instability on Synthesis of Zn2 SiO4-SiOx Core-Shell Nanotube Arrays and Their Cathodoluminescence Properties.

Vertically aligned Zn2SiO4-SiOx(x < 2) core-shell nanotube arrays consisting of Zn2SiO4-nanoparticle chains encapsulated into SiOx nanotubes and SiOx-coated Zn2SiO4 coaxial nanotubes were synthesized via one-step thermal annealing process using ZnO nanowire (ZNW) arrays as templates. The appearance of different nanotube morphologies was due to size-dependent thermal instability and specific melting of ZNWs. With an increase in ZNW diameter, the formation mechanism changed from decomposition of "etching" to Rayleigh instability and then to Kirkendall effect, consequently resulting in polycrystalline Zn2SiO4-SiOx coaxial nanotubes, single-crystalline Zn2SiO4-nanoparticle-chain-embedded SiOx nanotubes, and single-crystalline Zn2SiO4-SiOx coaxial nanotubes.

Unipolar assembly of zinc oxide rods manifesting polarity-driven collective luminescence.

Oriented assemblies of small crystals forming larger structures are common in nature and crucial for forthcoming technologies as they circumvent the difficulties of structural manipulation at microscopic scale. We have discovered two distinctive concentric assemblies of zinc oxide rods, wherein each rod has an intrinsically positive and a negative polar end induced by the noncentrosymmetric arrangement of Zn and O atoms. All the rods in a single assembly emanate out of a central core maintaining a single polar direction.

352 nm ultraviolet emission from high-quality crystalline AlN whiskers.

High-quality, crystalline AlN whiskers with large yield have been synthesized through the direct nitridation of Al vapor at high temperature. The AlN whiskers exhibited a strong and uniform ultraviolet emission at approximately 352 nm, which is notably shorter compared with the wavelength of previously reported one-dimensional AlN nanostructures. Energy filtered transmission electron microscope (TEM) analyses indicated that nitrogen deficiency and rather lower oxygen content in the AlN lattice might be responsible for the strong 352 nm ultraviolet emission.

Unpredicted nucleation of extended zinc blende phases in wurtzite ZnO nanotetrapod arms.

Tailoring the structural and electronic properties of 3D nanostructures via bottom-up techniques would pave the way for novel low-cost applications. One of such possibilities is offered by ZnO branched nanostructures like tetrapods, that have recently attracted attention for nanodevice applications from nanoelectronics to drug delivery. The conventional picture is that ZnO arms are thermodynamically stable only in the wurtzite phase.