Showing papers on "Cathodoluminescence published in 2012"
TL;DR: The present work opens the way both to fundamental studies of quantum confinement in closely packed quantum emitters and to characterizations of optoelectronic devices presenting carrier localization on the nanometer scale.
Abstract: We report the spectral imaging in the UV to visible range with nanometer scale resolution of closely packed GaN/AlN quantum disks in individual nanowires using an improved custom-made cathodoluminescence system. We demonstrate the possibility to measure full spectral features of individual quantum emitters as small as 1 nm and separated from each other by only a few nanometers and the ability to correlate their optical properties to their size, measured with atomic resolution. The direct correlation between the quantum disk size and emission wavelength provides evidence of the quantum confined Stark effect leading to an emission below the bulk GaN band gap for disks thicker than 2.6 nm. With the help of simulations, we show that the internal electric field in the studied quantum disks is smaller than what is expected in the quantum well case. We show evidence of a clear dispersion of the emission wavelengths of different quantum disks of identical size but different positions along the wire. This dispersion is systematically correlated to a change of the diameter of the AlN shell coating the wire and is thus attributed to the related strain variations along the wire. The present work opens the way both to fundamental studies of quantum confinement in closely packed quantum emitters and to characterizations of optoelectronic devices presenting carrier localization on the nanometer scale.
155 citations
TL;DR: Due to the excellent CL properties and good CIE chromaticity coordinates, the as-prepared Tb(3+))/Eu(3+)-doped CaYAlO(4) nanocrystalline phosphors have potential application in FEDs devices.
Abstract: Eu3+ and/or Tb3+-doped CaYAlO4 phosphor samples were synthesized by Pechini-type sol–gel method. X-Ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), photoluminescence (PL) and cathodoluminescence (CL) spectra were used to characterize the samples. For CaYAlO4:Tb3+, it is shown that the Tb3+-doping concentration has a significant effect on the 5D3/5D4 emission intensity of Tb3+, which is attributed to the cross relaxation from 5D3 to 5D4. Under the 4f8 → 4f75d excitation of Tb3+ or low-voltage electron beams excitation, the CaYAlO4:Tb3+ phosphors show tunable luminescence from blue to cyan, and then to green with the change of Tb3+-doping concentration. The CaYAlO4:Eu3+ samples exhibit a reddish-orange emission of Eu3+ corresponding to 5D0,1 → 7F0,1,2,3 transitions. Furthermore, a white emission can be realized in the single phase CaYAlO4 host by reasonably adjusting the doping concentrations of Tb3+ and Eu3+ under low-voltage electron beams excitation. Compared with the commercial blue (Y2SiO5:Ce3+) and green (ZnO:Zn) phosphors, CaYAlO4:0.1%Tb3+ and CaYAlO4:5%Tb3+ phosphors have higher CL intensity and stability under continuous electron bombardment. Due to the excellent CL properties and good CIE chromaticity coordinates, the as-prepared Tb3+/Eu3+-doped CaYAlO4 nanocrystalline phosphors have potential application in FEDs devices.
154 citations
TL;DR: The combined use of optical dark-field microscopy, cathodoluminescence, and electron energy-loss spectroscopy to study localized surface plasmons on individual gold nanodecahedra provides useful insight into the complex nature of plasmon resonances in nanoparticles with pentagonal symmetry.
Abstract: Imaging localized plasmon modes in noble- metal nanoparticles is of fundamental importance for applications such as ultrasensitive molecular detection. Here, we demonstrate the combined use of optical dark-field microscopy (DFM), cathodoluminescence (CL), and electron energy-loss spectroscopy (EELS) to study localized surface plasmons on individual gold nanodecahedra. By exciting surface plasmons with either external light or an electron beam, we experimentally resolve a prominent dipole-active plasmon band in the far-field radiation acquired via DFM and CL, whereas EELS reveals an additional plasmon mode associated with a weak dipole moment. We present measured spectra and intensity maps of plasmon modes in individual nanodecahedra in excellent agreement with boundary-element method simulations, including the effect of the substrate. A simple tight-binding model is formulated to successfully explain the rich plasmon structure in these particles encompasing bright and dark modes, which we predict to be fully observable in less lossy silver decahedra. Our work provides useful insight into the complex nature of plasmon resonances in nanoparticles with pentagonal symmetry.
152 citations
TL;DR: The results suggest that GaN nanorod arrays are suitable growth templates for efficient light-emitting diodes.
Abstract: Uniform GaN nanorod arrays are grown vertically by selective area growth on (left angle bracket 0001 right angle bracket) substrates. The GaN nanorods present six nonpolar {1⁻100} facets, which serve as growth surfaces for InGaN-based light-emitting diode quantum well active regions. Compared to growth on the polar {0001} plane, the piezoelectric fields in the multiple quantum wells (MQWs) can be eliminated when they are grown on nonpolar planes. The capability of growing ordered GaN nanorod arrays with different rod densities is demonstrated. Light emission from InGaN/GaN MQWs grown on the nonpolar facets is investigated by photoluminescence. Local emission from MQWs grown on different regions of GaN nanorods is studied by cathodoluminescence (CL). The core-shell structure of MQWs grown on GaN nanorods is investigated by cross-sectional transmission electron microscopy in both axial and radial directions. The results show that the active MQWs are predominantly grown on nonpolar planes of GaN nanorods, consistent with the observations from CL. The results suggest that GaN nanorod arrays are suitable growth templates for efficient light-emitting diodes.
146 citations
TL;DR: The obtained results indicated that the energy transfer process was quite opposite to the PL properties, and the cathodoluminescence properties of these phosphors show similar behavior as PL properties except the energyTransfer process.
Abstract: Trivalent rare-earth (RE) ions (Eu3+, Tb3+ and Sm3+) activated multicolor emitting SrY2O4 phosphors were synthesized by a sol–gel process. The structural and morphological studies were performed by the measurements of X-ray diffraction profiles and scanning electron microscope (SEM) images. The pure phase of SrY2O4 appeared after annealing at 1300 °C and the doping of RE ions did not show any effect on the structural properties. From the SEM images, the closely packed particles were observed due to the roughness of each particle tip. The photoluminescence (PL) analysis of individual RE ions activated SrY2O4 phosphors exhibits excellent emission properties in their respective regions. The Eu3+ co-activated SrY2O4:Tb3+ phosphor creates different emissions by controlling the energy transfer from Tb3+ to Eu3+ ions. Based on the excitation wavelengths, multiple (green, orange and white) emissions were obtained by Sm3+ ions co-activated with SrY2O4:Tb3+ phosphors. The decay measurements were carried out for analyzing the energy transfer efficiency and the possible ways of energy transfer from donor to acceptor. The cathodoluminescence properties of these phosphors show similar behavior as PL properties except the energy transfer process. The obtained results indicated that the energy transfer process was quite opposite to the PL properties. The calculated CIE chromaticity coordinates of RE ions activated SrY2O4 phosphors confirmed the red, green, orange and white emissions.
143 citations
TL;DR: An overview about CL properties of selected minerals is given, and several examples of applications discussed, to illustrate that best results are achieved when luminescence studies are performed under standardized conditions and combined with other analytical techniques with high sensitivity and high spatial resolution.
Abstract: Cathodoluminescence (CL) microscopy and spectroscopy are luminescence techniques with widespread applications in geosciences. Many rock-forming and accessory minerals show CL characteristics, which can be successfully used in geoscientific research. One of the most spectacular applications is the visualization of growth textures and other internal structures that are not discernable with other analytical techniques. In addition, information from CL imaging and spectroscopy can be used for the reconstruction of processes of mineral formation and alteration to provide information about the real structure of minerals and materials, and to prove the presence and type of lattice incorporation of several trace elements. In the present article, an overview about CL properties of selected minerals is given, and several examples of applications discussed. The presented data illustrate that best results are achieved when luminescence studies are performed under standardized conditions and combined with other analytical techniques with high sensitivity and high spatial resolution.
132 citations
TL;DR: The development of complete structural AlGaN-based deep-ultraviolet light-emitting diodes with an aluminum thin layer for increasing light extraction efficiency and a 217% enhancement in peak photoluminescence intensity is observed.
Abstract: We report the development of complete structural AlGaN-based deep-ultraviolet light-emitting diodes with an aluminum thin layer for increasing light extraction efficiency. A 217% enhancement in peak photoluminescence intensity at 294 nm is observed. Cathodoluminescence measurement demonstrates that the internal quantum efficiency of the deep-UV LEDs coated with Al layer is not enhanced. The emission enhancement of deep-UV LEDs is attributed to the higher LEE by the surface plasmon-transverse magnetic wave coupling. When the proportion of the TM wave to the Al layer increases with the Al content in the AlxGa1-xN multiple quantum wells, i.e., the band edge emission energy, the enhancement ratio of the Al-coated deep-UV LEDs increases.
109 citations
TL;DR: In this paper, a facile synthetic method for growing boron nitride-carbon (BN-C) phase-separated composite nanosheet coatings on silicon/silicon dioxide (Si/SiO2) substrates was developed.
Abstract: Motivated by the recent quest for producing novel two dimensional nanomaterials, we developed a facile synthetic method for growing boron nitride–carbon (BN–C) phase-separated composite nanosheet coatings on silicon/silicon dioxide (Si/SiO2) substrates. The coatings were composed of compact partially vertically aligned nanosheets with a nanoscale roughness. The majority of the obtained BN–C nanosheets were less than 5 nm in thickness, mostly consisting of 2–15 atomic layers. Electron energy loss spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed the natural sp2 hybridization of the product, and cathodoluminescence spectroscopy measurements showed strong luminescence emission in the ultraviolet region at room temperature. Ultraviolet-visible spectroscopy demonstrated that the composite structure of alternating BN and C domains has different optical band gap features compared to pure h-BN nanosheets and graphenes, making it a promising material for further fundamental physical studies and potential applications in optoelectronics. Moreover, due to the rough morphology and nanoscale features of the BN–C coatings, they exhibited excellent water repellency (superhydrophobicity).
94 citations
TL;DR: The results indicate that the use of water-diethyleneglycol (DEG) solvent mixture as the reaction medium not only allows facile particle size control but also endows the as-prepared samples with good water-solubility.
Abstract: In this paper, we demonstrate a simple, template-free, reproducible and one-step synthesis of hydrophilic KGdF4: Ln3+ (Ln = Ce, Eu, Tb and Dy) nanoparticles (NPs) via a solution-based route at room temperature. X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) and cathodoluminescence (CL) spectra are used to characterize the samples. The results indicate that the use of water–diethyleneglycol (DEG) solvent mixture as the reaction medium not only allows facile particle size control but also endows the as-prepared samples with good water-solubility. In particular, the mean size of NPs is monotonously reduced with the increase of DEG content, from 215 to 40 nm. The luminescence intensity and absolute quantum yields for KGdF4: Ce3+, Tb3+ NPs increase remarkably with particle sizes ranging from 40 to 215 nm. Additionally, we systematically investigate the magnetic and luminescence properties of KGdF4: Ln3+ (Ln = Ce, Eu, Tb and Dy) NPs. They display paramagnetic and superparamagnetic properties with mass magnetic susceptibility values of 1.03 × 10−4 emu g−1·Oe and 3.09 × 10−3 emu g−1·Oe at 300 K and 2 K, respectively, and multicolor emissions due to the energy transfer (ET) process Ce3+ → Gd3+ → (Gd3+)n → Ln3+, in which Gd3+ ions play an intermediate role in this process. Representatively, it is shown that the energy transfer from Ce3+ to Tb3+ occurs mainly via the dipole–quadrupole interaction by comparison of the theoretical calculation and experimental results. This kind of magnetic/luminescent dual-function materials may have promising applications in multiple biolabels and MR imaging.
90 citations
TL;DR: The results pave the way for the use of such nanoparticles for targeted labeling of surfaces to provide nanoscale mapping of molecular composition, indicated by cathodoluminescence colour, simultaneously acquired with structural electron images in a single instrument.
Abstract: Correlative light and electron microscopy promises to combine molecular specificity with nanoscale imaging resolution. However, there are substantial technical challenges including reliable co-registration of optical and electron images, and rapid optical signal degradation under electron beam irradiation. Here, we introduce a new approach to solve these problems: imaging of stable optical cathodoluminescence emitted in a scanning electron microscope by nanoparticles with controllable surface chemistry. We demonstrate well-correlated cathodoluminescence and secondary electron images using three species of semiconductor nanoparticles that contain defects providing stable, spectrally-distinguishable cathodoluminescence. We also demonstrate reliable surface functionalization of the particles. The results pave the way for the use of such nanoparticles for targeted labeling of surfaces to provide nanoscale mapping of molecular composition, indicated by cathodoluminescence colour, simultaneously acquired with structural electron images in a single instrument.
87 citations
01 Jan 2012
TL;DR: The potential of pegmatitic quartz veins of the Sierra de Comechigones (Argentina) as a source of high purity quartz by a combination of LA-ICP-MS, ICP, cathodoluminescence, gas chromatography, fluid inclusion analysis, Raman and FTIR spectroscopy was evaluated in this article.
Abstract: Classification, mineralogy and industrial potential of SiO2 minerals and rocks.- Assessment of High Purity Quartz Resources.- Quality requirements of quartz sand in the building industry.-Petrological and chemical characterisation of high-purity quartz deposits with examples from Norway.- Evaluation of the potential of the pegmatitic quartz veins of the Sierra de Comechigones (Argentina) as a source of high purity quartz by a combination of LA-ICP-MS, ICP, cathodoluminescence, gas chromatography, fluid inclusion analysis, Raman and FTIR spectroscopy.- Brazilian quartz deposits and a perspective about industrial use, gemstone and color treatment.- First-principles calculations of the E'1 center in quartz: Structural models, 29Si hyperfine parameters and association with Al impurity.- Gamma-Irradiation Dependency of EPR and TL-Spectra of Quartz.- Analysis of low element concentrations in quartz by electron microprobe.-In situ analysis of trace elements in quartz using laser ablation inductively coupled plasma mass spectrometry.- Cathodoluminescence microanalysis of the defect microstructures of bulk and nanoscale ultrapure SiO2 polymorphs for device applications.- Trace element characteristics, luminescence properties and real structure of quartz.- Mineralogy, geochemistry and cathodoluminescence of authigenic quartz from different sedimentary rocks.- CL textures and trace elements in hydrothermal quartz.- Quartz regeneration and the use of quartz as a carrier of genetic information.
TL;DR: The results indicate that the as-prepared Li(2)ZnGeO(4):Mn(2+) phosphor has a good CL intensity and CIE coordinate stability with green emission under low-voltage electron beam excitation, and is a promising green phosphor for application in full-color field-emission displays.
Abstract: Green emitting Li(2)ZnGeO(4):Mn(2+) phosphors were synthesized through a high temperature solid-state reaction process. X-Ray diffraction, field emission scanning electron microscopy, photoluminescence (PL) and cathodoluminescence (CL) spectra were utilized to characterize the synthesized samples. Under UV and electron-beam excitation, the pure Li(2)ZnGeO(4) sample shows a blue emission due to defects, while the Li(2)ZnGeO(4):Mn(2+) sample exhibits a green emission corresponding to the characteristic transition of Mn(2+) ((4)T(1)→(6)A(1)). In particular, the CL intensity (brightness) of Li(2)ZnGeO(4):Mn(2+) is higher than that of commercial green phosphor ZnO:Zn. In addition, the CL properties of Li(2)ZnGeO(4):Mn(2+) phosphor, the dependence of CL intensity on accelerating voltage and filament current, the decay behavior of CL intensity under electron bombardment, and the stability of CIE chromaticity coordinates, have been investigated in detail. The results indicate that the as-prepared Li(2)ZnGeO(4):Mn(2+) phosphor has a good CL intensity and CIE coordinate stability with green emission under low-voltage electron beam excitation. Therefore, Li(2)ZnGeO(4):Mn(2+) is a promising green phosphor for application in full-color field-emission displays.
TL;DR: It is demonstrated that InGaN island nucleation on GaN nanowires may be energetically favorable, depending on In content and nanowire diameter, and In inhomogeneities between the successive dots but also along the growth direction within each dot, which is attributed to compositional pulling.
Abstract: We demonstrate the strong influence of strain on the morphology and In content of InGaN insertions in GaN nanowires, in agreement with theoretical predictions which establish that InGaN island nucleation on GaN nanowires may be energetically favorable, depending on In content and nanowire diameter. EDX analyses reveal In inhomogeneities between the successive dots but also along the growth direction within each dot, which is attributed to compositional pulling. Nanometer-resolved cathodoluminescence on single nanowires allowed us to probe the luminescence of single dots, revealing enhanced luminescence from the high In content top part with respect to the lower In content dot base.
TL;DR: In this paper, the authors suggest that the sub-surface structure of the trench defect consists of a basal plane stacking fault bounded by a stacking mismatch boundary, which terminates at the apex of a V-shaped trench.
Abstract: In a wide variety of InGaN/GaN quantum well (QW) structures, defects are observed which consist of a trench partially or fully enclosing a region of the QW having altered emission properties. For various different defect morphologies, cathodoluminescence studies suggest that the emission is redshifted in the enclosed region. Based on transmission electron microscopy and atomic force microscopy data, we suggest that the sub-surface structure of the trench defect consists of a basal plane stacking fault bounded by a stacking mismatch boundary, which terminates at the apex of a V-shaped trench.
TL;DR: Application of cathodoluminescence (CL) spectroscopy to volcanic quartz and its utility in assessing variation in trace quantities of Ti within individual crystals is considered and maps of Ti variation can be produced by calibration of the CL spectral data against relatively few analytical points.
Abstract: This article concerns application of cathodoluminescence (CL) spectroscopy to volcanic quartz and its utility in assessing variation in trace quantities of Ti within individual crystals. CL spectroscopy provides useful details of intragrain compositional variability and structure but generally limited quantitative information on element abundances. Microbeam analysis can provide such information but is time-consuming and costly, particularly if large numbers of analyses are required. To maximize advantages of both approaches, natural and synthetic quartz crystals were studied using high-resolution hyperspectral CL imaging (1.2-5.0 eV range) combined with analysis via laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Spectral intensities can be deconvolved into three principal contributions (1.93, 2.19, and 2.72 eV), for which intensity of the latter peak was found to correlate directly with Ti concentration. Quantitative maps of Ti variation can be produced by calibration of the CL spectral data against relatively few analytical points. Such maps provide useful information concerning intragrain zoning or heterogeneity of Ti contents with the sensitivity of LA-ICPMS analysis and spatial resolution of electron microprobe analysis.
TL;DR: In this article, a template-free, low temperature, facile single step solvothermal approach is used to construct a cubic single crystalline CeO2 nanoparticles grown on the edges of tapered ZnO nanorods with definite orientations and alignments.
Abstract: The present investigation explores the controlled architecture of a CeO2–ZnO nanocomposite via a template-free, low temperature, facile single step solvothermal approach. This complex architecture depicts cubic single crystalline CeO2 nanoparticles (size ∼15 nm) grown on the edges of tapered ZnO nanorods with definite orientations and alignments. The formation of wurtzite ZnO, cubic CeO2 and the coexistence of Ce3+ and Ce4+ on the surface of the CeO2–ZnO nanocomposites are confirmed using various characterization tools. The finding of such unique nanostructures by a facile method is exemplified by a plausible growth mechanism. Surprisingly, the aqueous mediated ultrasonication reaction conferred the formation of crystalline ZnO nanotubes of diameter ∼50 nm. Spatially resolved cathodoluminescence spectra are obtained by linearly scanning an individual CeO2–ZnO nanorod along its length, which reveals the size-dependent surface effects. Interestingly, such hybrid CeO2–ZnO nanoarchitecture is observed to exhibit enhanced field emission properties, demonstrating better current stability as compared to other ZnO nanostructures. This is attributed mainly to strong surface interactions between the Ce-ionic species and the ZnO nanorods. Herein, a soft-chemical approach is used for the first time to architect a binary oxide nanostructure, which is otherwise accomplished using high temperature techniques, as reported elsewhere. Also, the present work not only gives insight into understanding the hierarchical growth behaviour of the CeO2–ZnO nanocomposite in a solution phase synthetic system, but also provides an efficient route to enhance the field emission performance of ZnO nanostructures, which could be extended to other potential applications, such as chemical sensors, optoelectronic devices and photocatalysts.
TL;DR: In this paper, the authors used electrochemistry-assisted laser ablation in liquids (ECLAL) to synthesize zinc molybdate nanoplates and nanorods with different phases.
Abstract: Electrochemistry-assisted laser ablation in liquids (ECLAL) is a chemically “simple and clean” synthesis of nanoparticles. Using ECLAL, we have synthesized zinc molybdate nanoplates and nanorods with two different phases. These two nanostructures are characterized carefully by scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, Fourier transform infrared spectroscopy, Raman scattering spectroscopy, and UV–vis spectrophotometry. On the basis of the cathodoluminescence measurements, we observe that the nanoplates emit no light, while the nanorods give out green light before annealing. The optical properties of both get much better after annealing, which indicates their potential applications in photoelectric nanodevices. The basic physics and chemistry involved in the ECLAL fabrication and the luminescence mechanism for products before and after annealing are discussed.
TL;DR: The spectrally and spatially resolved cathodoluminescence of diamond nanoparticles using focused fast electron beams in a transmission electron microscope is reported and a shift of the zero phonon line (ZPL) between the two emitters is shown to arise even within the same nanoparticle.
Abstract: Here we report the spectrally and spatially resolved cathodoluminescence of diamond nanoparticles using focused fast electron beams in a transmission electron microscope. We demonstrate the possibility of quickly detecting various individual colour centres of different kinds on wide areas (several micrometres square) contained in nanoparticles separated by subwavelength distances. Among them, nanoparticles containing one or more neutral nitrogen-vacancy (NV(0)) intensity maxima have been seen, attributable to individual emitters. Thanks to a spatial resolution which is solely limited by charge carrier diffusion in the case of a fast electron (80 keV) setup, the spectra of two individual NV(0) emitters separated by 80 nm inside a nanoparticle have been spatially discerned. A shift of the zero phonon line (ZPL) between the two emitters, which we attribute to internal stress, is shown to arise even within the same nanoparticle. Detailed emission spectra (ZPL, phonon lines and Huang-Rhys factor, directly linked to the relaxation energy of the colour centre) in 51 individual NV(0) centres have been measured in 39 particles. The ZPL and Huang-Rhys factor are found to be measurably dispersed, while the phonon energies keep constant.
TL;DR: In this article, the spatial maps of localized surface plasmon resonances associated with photon emission in a truncated tetrahedral gold nanoparticle on a silicon substrate were reported.
Abstract: We report the spatial maps of the localized surface plasmon resonances associated photon emission in a truncated tetrahedral gold nanoparticle on a silicon substrate. Site-specific cathodoluminescence spectroscopy and imaging in a scanning electron microscope shows stronger photon emission in the visible range near the tips of the particle in contact with the substrate compared to the edges of the particle. Strong local field variations on a length scale as short as 19 nm are resolved. We also perform FDTD simulations of both the spectra and, for the first time, the full cathodoluminescence images. Excellent agreement is obtained with the experimental results, and the detailed information available from the simulated results makes it possible to identify the signature of out-of-plane higher order modes in the truncated tetrahedral gold particle.
TL;DR: The synthetic details, investigations into the phase purity and the presence of the oxocarbonate anion CO(3)(2-) proven by IR measurements and EDX, as well as X-ray powder diffraction data, are given.
Abstract: Uniform LaOF and LaOF : Eu3+ nanocrystals of the γ-form have been successfully synthesized under mild conditions via a facile hydrothermal method followed a heat treatment of their bastnaesite-type precursor (LaCO3F). The synthetic details, investigations into the phase purity and the presence of the oxocarbonate anion CO32– proven by IR measurements and EDX, as well as X-ray powder diffraction data, are given. Photoluminescence (PL) and cathodoluminescence (CL) spectra were utilized to characterize the luminescence properties of the LaCO3F : Eu3+ and LaOF : Eu3+ samples. Under ultraviolet light excitation, the LaCO3F : Eu3+ precursor shows an orange emission of Eu3+ (dominated by 5D0 → 7F1), while the product of heat treatment, LaOF : Eu3+, shows the characteristic emissions of Eu3+ (5DJ → 7FJ′J, J′ = 0, 1, 2, 3 transitions). Under the excitation of UV and low-voltage electron beams, the emission color (including white) of LaOF : Eu3+ can be tuned by adjusting the doping concentration of Eu3+. The corresponding luminescence mechanisms have been discussed in detail.
TL;DR: In this paper, a core-shell InGaN/GaN multiple quantum well (MQW) on GaN nanopillars was fabricated by top-down etching followed by epitaxial regrowth.
Abstract: Core-shell InGaN/GaN multiple quantum wells (MQWs) on GaN nanopillars were fabricated by top-down etching followed by epitaxial regrowth. The regrowth formed hexagonal sidewalls and pyramids on the nanopillars. The cathodoluminescence of MQWs blue shifts as the location moves from top to bottom on both the pillar sidewalls and pyramid facets, covering a spectral linewidth of about 100 nm. The MQWs on the pillar sidewalls have a higher InN fraction than those on the pyramid facets. The photoluminescent wavelength is stable over two orders of carrier density change due to the smaller quantum confined Stark effect on the nanopillar facets.
TL;DR: In this article, a table of contents image illustrates the strain-gradient effect on the optical-electronic properties in a bent ZnO microwire, with a much stronger red-shift on the outer tensile side than a blue shift on the inner compressive side.
Abstract: The table of contents image illustrates the strain-gradient effect on the optical-electronic properties in a bent ZnO microwire, with a much stronger red-shift on the outer tensile side than a blue-shift on the inner compressive side. The low temperature cathodoluminescence cross-sectional scanning spectra on the strain-neutral middle-plane are highlighted by thicker black lines, which clearly shows a strain-gradient induced red-shift.
TL;DR: In this article, a stable monoclinic α-phase of Bi_2O_3 has been sintered at temperatures of 500 °C and 750 °C in air or in nitrogen atmospheres.
TL;DR: Light emitting diodes fabricated using ensembles of free-standing (In, Ga)N/GaN nanowires (NWs) grown on Si substrates in the self-induced growth mode by molecular beam epitaxy exhibit N-polarity and are subject to a non-vanishing quantum confined Stark effect.
Abstract: Light emitting diodes (LEDs) have been fabricated using ensembles of free-standing (In, Ga)N/GaN nanowires (NWs) grown on Si substrates in the self-induced growth mode by molecular beam epitaxy. Electron-beam-induced current analysis, cathodoluminescence as well as biased μ-photoluminescence spectroscopy, transmission electron microscopy, and electrical measurements indicate that the electroluminescence of such LEDs is governed by the differences in the individual current densities of the single-NW LEDs operated in parallel, i.e. by the inhomogeneity of the current path in the ensemble LED. In addition, the optoelectronic characterization leads to the conclusion that these NWs exhibit N-polarity and that the (In, Ga)N quantum well states in the NWs are subject to a non-vanishing quantum confined Stark effect.
TL;DR: An AlN phosphor that was coactivated by Ce3+ and Si4+ ions was synthesized by gas pressure sintering (GPS) at 2050 °C for 4 h in a 0.92 MPa nitrogen atmosphere as mentioned in this paper.
Abstract: An AlN phosphor that was coactivated by Ce3+ and Si4+ ions was synthesized by gas pressure sintering (GPS) at 2050 °C for 4 h in a 0.92 MPa nitrogen atmosphere. The phosphor emits blue color with the Commission International de l’Eclairage (CIE) chromaticity coordinate of (0.15, 0.07), which is close to the National Television Standard Committee (NTSC) blue coordinate. The crystallization and cell parameters of the samples were investigated by Rietveld refinement and high-resolution transmission electron microscopy (HRTEM). Since the ionic size of Ce3+ ions are much larger than that of Al3+ ions, the locations of rare earth (RE) ions in the AlN lattice are unclear. An octahedral interstitial site inside the wurtzite structure is proposed to be the site for RE ions. The effect of Si substitution was verified by energy-dispersive X-ray spectroscopy (EDX) and solid-state nuclear magnetic resonance (ssNMR). Cathodoluminescence (CL) was examined under electron bombardment at different accelerating voltages. Ni...
TL;DR: The influence of indium doping on morphology, structural, and luminescence properties of gallium oxide micro-and nanostructures is reported in this article, showing that indium plays a major role in the observed morphologies and support the assumption of a layer by layer model as growth mechanism.
Abstract: The influence of indium doping on morphology, structural, and luminescence properties of gallium oxide micro- and nanostructures is reported Indium-doped gallium oxide micro- and nanostructures have been grown by thermal oxidation of metallic gallium in the presence of indium oxide The dominant morphologies are beltlike structures, which in many cases are twisted leading to springlike structures, showing that In diffusion in Ga2O3 influences the microstructure shapes High-resolution transmission electron microscopy has revealed the presence of twins in the belts, and energy-dispersive X-ray spectroscopy in the scanning electron microscopy (SEM) has detected a segregation of indium impurities at the edges of planar structures These results suggest that indium plays a major role in the observed morphologies and support the assumption of a layer by layer model as growth mechanism An additional assessment of indium influence on the defect structure has been performed by cathodoluminescence in the SEM, X-ray photoelectron microscopy, and spatially resolved Raman spectroscopy
TL;DR: In this paper, uniform Y2O3:Ln3+ (Ln 3+ = Eu3+, Tb3+) hollow microspheres have been successfully prepared via a urea-assisted homogeneous precipitation method using polystyrene (PS) as templates, followed by a subsequent calcination process.
Abstract: Well-dispersed, uniform Y2O3:Ln3+ (Ln3+ = Eu3+, Tb3+) hollow microspheres have been successfully prepared via a urea-assisted homogeneous precipitation method using polystyrene (PS) as templates, followed by a subsequent calcination process. X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), photoluminescence (PL) spectra, and cathodoluminescence (CL) spectra were employed to characterize the samples. The results demonstrate that the samples can be well indexed to the pure cubic phase of Y2O3. The TEM and SEM images indicate that the shell of the uniform hollow spheres, whose diameter is about 2.1 μm, is composed of many uniform nanoparticles with diameters of around 20 nm. Upon ultraviolet (UV) and low-voltage electron beam excitation, the Y2O3:Ln3+ (Ln3+ = Eu3+, Tb3+) samples exhibit bright red (Eu3+, 5D0 → 7F2), and green (Tb3+, 5D4 → 7F5) luminescence. This material may find potential applications in light display systems, optoelectronic devices and drug delivery based on the uniform hollow structure, dimensions, and luminescence properties. Furthermore, this synthesis route may be of great significance in the preparation of other hollow spherical materials.
TL;DR: Computer simulation provided a quantitative analysis of the mini-band energies in the AlN/GaN superlattices and suggested the observed blue-shifted emission corresponds to the interband transitions between the second subbands of GaN, as a result of quantum confinement and strain effect in these AlN /GaN MQW nanowire structures.
Abstract: We report the controlled synthesis of AlN/GaN multi-quantum well (MQW) radial nanowire heterostructures by metal–organic chemical vapor deposition. The structure consists of a single-crystal GaN nanowire core and an epitaxially grown (AlN/GaN)m (m = 3, 13) MQW shell. Optical excitation of individual MQW nanowires yielded strong, blue-shifted photoluminescence in the range 340–360 nm, with respect to the GaN near band-edge emission at 368.8 nm. Cathodoluminescence analysis on the cross-sectional MQW nanowire samples showed that the blue-shifted ultraviolet luminescence originated from the GaN quantum wells, while the defect-associated yellow luminescence was emitted from the GaN core. Computational simulation provided a quantitative analysis of the mini-band energies in the AlN/GaN superlattices and suggested the observed blue-shifted emission corresponds to the interband transitions between the second subbands of GaN, as a result of quantum confinement and strain effect in these AlN/GaN MQW nanowire struc...
TL;DR: Hyperspectral cathodoluminescence imaging provides spectrally and spatially resolved information on luminescent materials within a single dataset, and its instrumentation and data treatment methods address the challenge of generating low-noise images.
Abstract: Hyperspectral cathodoluminescence imaging provides spectrally and spatially resolved information on luminescent materials within a single dataset. Pushing the technique toward its ultimate nanoscale spatial limit, while at the same time spectrally dispersing the collected light before detection, increases the challenge of generating low-noise images. This article describes aspects of the instrumentation, and in particular data treatment methods, which address this problem. The methods are demonstrated by applying them to the analysis of nanoscale defect features and fabricated nanostructures in III-nitride-based materials.
TL;DR: In this article, Nanocrystalline Ca2Gd8Si6O26 (CGS) phosphors were synthesized by solvothermal reaction method and the structural and morphological properties of the samples were evaluated by X-ray diffraction and scanning electron microscopy.
Abstract: Nanocrystalline Ca2Gd8Si6O26 (CGS): Sm3+ phosphors were synthesized by solvothermal reaction method. The structural and morphological properties of the samples were evaluated by X-ray diffraction and scanning electron microscopy. The photoluminescence excitation and emission spectra along with decay properties were investigated as a function of Sm3+ concentration. Under 405 nm excitation wavelength, the photoluminescence spectra showed three emission peaks at 565 nm (4G5/2 → 6H5/2) and at 650 nm (4G5/2 → 6H9/2), and with an intense orange emission at 600 nm (4G5/2 → 6H7/2). Based on the orange emission performance, the Sm3+ concentration was optimized to be at 2 mol%. The low voltage cathodoluminescence (CL) properties were also performed for 2 mol% Sm3+-doped CGS phosphors as a function of accelerating voltage (1–5 kV). From the CL spectra, the reddish-orange emission was observed. The calculated Commission International De I-Eclairage chromaticity coordinates are in close proximity to the chromaticity coordinates of Nichia corporation developed amber light emitting diodes.