Showing papers on "Cathodoluminescence published in 2013"
TL;DR: In this paper, temperature-dependent cathodoluminescence spectra were measured from (001) unintentionally doped, (100) Si-doped, and (010) Mgdoped β-Ga2O3 substrates prepared by either the floating zone growth or edge-defined film-fed growth methods.
Abstract: Temperature-dependent cathodoluminescence spectra were measured from (001) unintentionally doped, (100) Si-doped, and (010) Mg-doped β-Ga2O3 substrates prepared by either the floating zone growth or edge-defined film-fed growth methods. Although β-Ga2O3 is expected to be an indirect bandgap material, direct Γ-Γ transitions were found to be dominant in the optical transmittance spectra. The substrates exhibited no near-band-edge emission and instead exhibited ultraviolet luminescence, blue luminescence (BL), and green luminescence bands. Since the BL intensity strongly depended on the resistivity in the crystals, there was evidence of a correlation between the BL intensity and formation energy of oxygen vacancies.
245 citations
TL;DR: In this article, the synthesis and crystal structure of a novel phosphate family, Ca19Mg2(PO4)14 (M = Mg, Zn, Mn), were investigated.
Abstract: In order to explore a new family of phosphate phosphors, the synthesis and crystal structure of a novel phosphate family, Ca19M2(PO4)14 (M = Mg, Zn, Mn), were investigated. Eu3+ doped Ca19Mg2(PO4)14 red phosphor was also successfully synthesized with the objective of application in ultraviolet-based light-emitting diodes (LEDs) and field emission displays (FEDs). The characteristic photoluminescence properties were studied in detail by photoluminescence excitation (PLE), emission (PL) spectra and decay times. The Ca19Mg2(PO4)14:0.06Eu3+ phosphor offers higher brightness and thermal stability than the commercial Y2O3:Eu3+. The unexpected temperature-dependent luminescence from higher 5D1 states was observed and was explained via the configuration coordinate diagram. The cathodoluminescence (CL) spectra as a function of accelerating voltage and probe current were also measured. Excellent degradation properties with good color stability were obtained by continuous low-voltage electron-beam excitation of the phosphor. The results indicate that the phosphor Ca19Mg2(PO4)14:0.06Eu3+ can be a suitable red-emitting phosphor candidate for LEDs and FEDs.
168 citations
TL;DR: In this paper, a deterministic fabrication of sub-μm mesa-structures containing single quantum dots (QDs) by in situ electron-beam lithography was reported.
Abstract: We report on the deterministic fabrication of sub-μm mesa-structures containing single quantum dots (QDs) by in situ electron-beam lithography. The fabrication method is based on a two-step lithography process: After detecting the position and spectral features of single InGaAs QDs by cathodoluminescence (CL) spectroscopy, circular sub-μm mesa-structures are defined by high-resolution electron-beam lithography and subsequent etching. Micro-photoluminescence spectroscopy demonstrates the high optical quality of the single-QD mesa-structures with emission linewidths below 15 μeV and g(2)(0) = 0.04. Our lithography method has an alignment precision better than 100 nm which paves the way for a fully deterministic device technology using in situ CL lithography.
102 citations
TL;DR: Under the low voltage electron beam excitation, Tb(3+) ion doped Ca2Ba3(PO4)3Cl samples present different luminescence properties compared with their PL spectra, which is ascribed to the different excitation mechanism.
Abstract: Pure Ca2Ba3(PO4)3Cl and rare earth ion (Eu2+/Ce3+/Dy3+/Tb3+) doped Ca2Ba3(PO4)3Cl phosphors with the apatite structure have been prepared via a Pechini-type sol–gel process. X-ray diffraction (XRD) and structure refinement, photoluminescence (PL) spectra, cathodoluminescence (CL) spectra, absolute quantum yield, as well as lifetimes were utilized to characterize samples. Under UV light excitation, the undoped Ca2Ba3(PO4)3Cl sample shows broad band photoluminescence centered near 480 nm after being reduced due to the defect structure. Eu2+ and Ce3+ ion doped Ca2Ba3(PO4)3Cl samples also show broad 5d → 4f transitions with cyan and blue colors and higher quantum yields (72% for Ca2Ba3(PO4)3Cl:0.04Eu2+; 67% for Ca2Ba3(PO4)3Cl:0.016Ce3+). For Dy3+ and Tb3+ doped Ca2Ba3(PO4)3Cl samples, they give strong line emissions coming from 4f → 4f transitions. Moreover, the Ce3+ ion can transfer its energy to the Tb3+ ion in the Ca2Ba3(PO4)3Cl host, and the energy transfer mechanism has been demonstrated to be a resonant...
102 citations
TL;DR: The mechanism behind quantum states generation in an electron microscope is unveiled, and it is shown that it clearly makes cathodoluminescence the nanometer scale analog of photoluminecence.
Abstract: We report on the experimental demonstration of single-photon state generation and characterization in an electron microscope. In this aim we have used low intensity relativistic (energy between 60 and 100 keV) electrons beams focused in a ca. 1 nm probe to excite diamond nanoparticles. This triggered individual neutral nitrogen-vacancy centers to emit photons which could be gathered and sent to a Hanbury Brown-Twiss intensity interferometer. The detection of a dip in the correlation function at small time delays clearly demonstrates antibunching and thus the creation of nonclassical light states. Specifically, we have also demonstrated single-photon states detection. We unveil the mechanism behind quantum states generation in an electron microscope, and show that it clearly makes cathodoluminescence the nanometer scale analog of photoluminescence. By using an extremely small electron probe size and the ability to monitor its position with subnanometer resolution, we also show the possibility of measuring the quantum character of the emitted beam with deep subwavelength resolution.
97 citations
TL;DR: Overall, the feasibility of obtaining low defect and strain free m-plane coaxial NWs using pulsed MOCVD can be utilized for the realization of high-power LEDs without an efficiency droop.
Abstract: We report the growth of high-quality nonpolar (m-plane) and semipolar (r-plane) multiple quantum well (MQW) nanowires (NWs) for high internal quantum efficiency light emitting diodes (LEDs) without polarization. Highly aligned and uniform In(x)Ga(1-x)N/GaN MQW layers are grown coaxially on the {1-100} sidewalls of hexagonal c-axis n-GaN NWs on Si(111) substrates by a pulsed flow metal-organic chemical vapor deposition (MOCVD) technique. The photoluminescence (PL) measurements reveal that the wavelength and intensity of an MQW structure with various pairs (2-20) are very stable and possess composition-dependent emission ranging from 369 to 600 nm. The cathodoluminescence (CL) spectrum of individual In(x)Ga(1-x)N/GaN MQW NW is dominated by band-edge emission at 369 and 440 nm with a relatively homogeneous profile of parallel alignment. High-resolution transmission electron microscopy (HR-TEM) studies of coaxial InxGa1-xN/GaN MQW NWs measured along the [0001] and [2-1-10] zone axes reveal that the grown NWs are uniform with six nonpolar m-plane facets without any dislocations and stacking faults. The p-GaN/In(x)Ga(1-x)N/GaN MQW/n-GaN NW coaxial LEDs show a current rectification with a sharp onset voltage at 2.65 V in the forward bias. The linear enhancement of power output could be attributed to the elimination of piezoelectric fields in the In(x)Ga(1-x)N/GaN MQW active region. The superior performance of coaxial NW LEDs is observed in comparison with that of thin film LEDs. Overall, the feasibility of obtaining low defect and strain free m-plane coaxial NWs using pulsed MOCVD can be utilized for the realization of high-power LEDs without an efficiency droop. These kinds of coaxial NWs are viable high surface area MQW structures which can be used to enhance the efficiency of LEDs.
95 citations
TL;DR: Tomographic analysis of the In distribution, interface morphology, and dopant clustering of InGaN/GaN multiquantum wells in LEDs reveals material quality comparable to that of planar LED QWs.
Abstract: Correlated atom probe tomography, cross-sectional scanning transmission electron microscopy, and cathodoluminescence spectroscopy are used to analyze InGaN/GaN multiquantum wells (QWs) in nanowire array light-emitting diodes (LEDs). Tomographic analysis of the In distribution, interface morphology, and dopant clustering reveals material quality comparable to that of planar LED QWs. The position-dependent CL emission wavelength of the nonpolar side-facet QWs and semipolar top QWs is correlated with In composition.
94 citations
TL;DR: In this article, Si-doped Al0.6Ga0.4N films were studied using deep ultraviolet timeresolved photoluminescence and time-resolved cathodolumininescence spectroscopies.
Abstract: Luminescence dynamics for the near-band-edge (NBE) emission peak at around 250 nm of c-plane Si-doped Al0.6Ga0.4N films grown on AlN templates by low-pressure metalorganic vapor phase epitaxy were studied using deep ultraviolet time-resolved photoluminescence and time-resolved cathodoluminescence spectroscopies. For the films with the Si-doping concentration, [Si], lower than 1.9 × 1017 cm–3, the doping lessened the concentration of cation vacancies, [VIII], through the surfactant effect or the aid of the reactant doping in a form of H3SiNH2. However, the room-temperature nonradiative lifetime, and, consequently, the equivalent value of internal quantum efficiency in the weak excitation regime steeply decreased when [Si] exceeded 1018 cm−3. Simultaneously, the intensity ratio of the deep-state emission band to the NBE emission abruptly increased. Because the increase in [Si] essentially gives rise to the increase in [VIII] (for [Si]>1.9×1017 cm−3) and the overcompensation of Si is eventually observed for ...
93 citations
TL;DR: In this paper, the authors investigated the cathodoluminescence (CL) emission and the Raman spectra along individual ZnO nanorods grown by a catalyst-free method.
Abstract: We have investigated the cathodoluminescence (CL) emission and the Raman spectra along individual ZnO nanorods grown by a catalyst-free method. The spatial correlation between the CL emission and the defect related Raman modes permits establishing a correspondence between the non-radiative recombination centres (NRRCs) and the defects responsible for the 275 cm−1 Raman band. According to this relation, the NRRCs in these nanorods are tentatively associated with complexes of zinc interstitials.
92 citations
TL;DR: In this article, a series of single-composition phosphors Ca5(PO4)2SiO4:Ce3+, Tb3+, Mn2+ have been prepared via a high-temperature solid-state reaction process.
Abstract: A series of single-composition phosphors Ca5(PO4)2SiO4:Ce3+, Tb3+, Mn2+ have been prepared via a high-temperature solid-state reaction process. The Ce3+ emission at different lattice sites has been identified and discussed. The energy transfer from Ce3+ to Tb3+ and Mn2+ ions has been validated. The emissive colors of Ca5(PO4)2SiO4:Ce3+, Tb3+/Mn2+ samples can be adjusted from blue to green and from blue to red-orange by the energy transfer of Ce3+ → Tb3+ and Ce3+ → Mn2+, respectively. More importantly, white emission has been obtained through adjusting the relative concentrations of Ce3+, Tb3+ and Mn2+ ions in the Ca5(PO4)2SiO4 host under UV and low-voltage electron beam excitation, respectively. Additionally, the temperature-dependent photoluminescence and the degradation behaviors of cathodoluminescence under continuous electron bombardment for as-prepared phosphors have been investigated in detail. The results reveal that the Ca5(PO4)2SiO4 host is stable enough to protect the photoluminescence and cathodoluminescence properties of Ce3+, Tb3+ and Mn2+ ions from being affected. Tunable luminescence and the stable structure suggest that Ca5(PO4)2SiO4:Ce3+/Tb3+/Mn2+ phosphors have great potential in the application in WLEDs and FEDs.
92 citations
TL;DR: An analytical model is developed that describes the resonant Mie-like optical eigenmodes in the silicon cylinders using an effective index of a slab waveguide mode and enables qualification of all resonances with azimuthal and radial quantum numbers.
Abstract: High-index dielectric or semiconductor nanoparticles support strong Mie-like geometrical resonances in the visible spectral range. We use 30 keV angle-resolved cathodoluminescence imaging spectroscopy to excite and detect these resonant modes in single silicon nanocylinders with diameters ranging from 60 to 350 nm. Resonances are observed with wavelengths in the range of 400–700 nm, with quality factors in the range Q = 9–77, and show a strong red shift with increasing cylinder diameter. The photonic wave function of all modes is determined at deep-subwavelength resolution and shows good correspondence with numerical simulations. An analytical model is developed that describes the resonant Mie-like optical eigenmodes in the silicon cylinders using an effective index of a slab waveguide mode. It shows good overall agreement with the experimental results and enables qualification of all resonances with azimuthal (m = 0–4) and radial (q = 1–4) quantum numbers. The single resonant Si nanocylinders show charac...
TL;DR: In this paper, Nanocrystalline GdNbO4:Tm3+ and GdnbO 4:Dy3+ phosphors were prepared through a Pechini-type sol gel process.
Abstract: Nanocrystalline GdNbO4:Tm3+ and GdNbO4:Dy3+ phosphors were prepared through a Pechini-type sol gel process. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, and cathodoluminescence (CL) spectra were utilized to characterize the synthesized phosphors. XRD reveals that the samples begin to crystallize at 900 degrees C and the pure GdNbO4 phase can be obtained at 1000 degrees C. FE-SEM images indicate that the GdNbO4:Tm3+ and GdNbO4:Dy3+ samples consist of fine and spherical grains with a size around 30-50 nm. Under the excitation of UV light (264 nm) and low-voltage electron beams (1-3 kV), the GdNbO4:Tm3+ and GdNbO4:Dy3+ phosphors showed the characteristic emissions of Tm3+ (D-1(2) -> H-3(6), H-3(5), H-3(4), and (1)G(4) -> H-3(6) transitions) and Dy3+ (F-4(9/2) -> H-6(15/2) and F-4(9/2) -> H-6(13/2) transitions), respectively. The blue CL of the GdNbO4:Tm3+ phosphor has higher color purity and comparable intensity to the Y2SiO5:Ce3+ commercial product. A single-composition white light emitting in response to near UV and low-voltage electron beam excitation has been realized in GdNbO4:Dy3+ phosphor. The obtained GdNbO4:Tm3+ and GdNbO4:Dy3+ phosphors have potential applications in the areas of near UV white-light-emitting diodes and field emission display devices.
TL;DR: In this paper, the physical principles of growth of Ga-polar GaN three-dimensional columns are identified, and their potential for manipulating the growth process is discussed, where the shells of InGaN/GaN multi quantum wells and p-GaN have been realized on a core of n-doped GaN column.
Abstract: Arrays of dislocation free uniform Ga-polar GaN columns have been realized on patterned SiOx/GaN/sapphire templates by metal organic vapor phase epitaxy using a continuous growth mode. The key parameters and the physical principles of growth of Ga-polar GaN three-dimensional columns are identified, and their potential for manipulating the growth process is discussed. High aspect ratio columns have been achieved using silane during the growth, leading to n-type columns. The vertical growth rate increases with increasing silane flow. In a core–shell columnar LED structure, the shells of InGaN/GaN multi quantum wells and p-GaN have been realized on a core of n-doped GaN column. Cathodoluminescence gives insight into the inner structure of these core–shell LED structures.
TL;DR: In this paper, two series of K1−xNaxSrPO4:0.005Eu2+, yTb3+ phosphors are synthesized via a high-temperature solid-state reaction and their emission color can be tuned from deep blue to blue-green by modulating the crystal field strength and energy transfer.
Abstract: Two series of K1−xNaxSrPO4:0.005Eu2+ and K0.4Na0.6Sr0.995−yPO4:0.005Eu2+, yTb3+ phosphors are synthesized via a high-temperature solid-state reaction. Their emission color can be tuned from deep blue to blue–green by modulating the crystal field strength and energy transfer. Partial substitution of K+ with Na+ results in a contraction and distortion of the unit cell of the K1−xNaxSr0.995PO4:0.005Eu2+ host, tuning the emission from 426 to 498 nm. The red-shifted emission is attributed to an increased crystal field splitting for Eu2+ in a lowered symmetry crystal field. The tunable emission is further demonstrated in the cathodoluminescence spectra, which indicates that the luminescence distribution of the K1−xNaxSr0.995PO4:0.005Eu2+ phosphor is very homogenous. Additionally, utilizing the principle of energy transfer, the emission color can be further tuned by co-doping with Tb3+. The chromaticity coordinates for the co-doped phosphor, K0.4Na0.6Sr0.995−yPO4:0.005Eu2+, yTb3+, can be adjusted from (0.202, 0.406) for y = 0 to (0.232, 0.420) for y = 0.09. The energy transfer processes from the sensitizer (Eu2+) to the activator (Tb3+) are studied and demonstrated to have a resonance-type dipole–dipole interaction mechanism, with the critical distance of the energy transfer calculated to be 12.46 A using a concentration quenching method.
TL;DR: The as-prepared phosphors might be promising for use in field-emission display (FED) devices and the cathodoluminescence properties of SrY2O4: Tb(3+)/Tm(3 +)/Dy(3+) phosphors including the dependence of CL intensity on accelerating voltage and filament current, the decay behaviour of CLintensity under electron bombardment, and the stability of CIE chromaticity coordinate have been investigated in detail.
Abstract: Tb3+, Tm3+, and Dy3+-activated SrY2O4 phosphors have been prepared via Pechini-type sol–gel method. X-Ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL) and lifetimes, as well as cathodoluminescence (CL) spectra were used to characterize the samples. Under low-voltage electron beam excitation, the Tb3+-doped samples show a green luminescence, with a better CIE coordinates and higher emission intensity than the commercial product ZnO: Zn. Blue and yellow emissions could be obtained by doping with Tm3+ and Dy3+, respectively. A color-tunable emission in SrY2O4 phosphors can be realized by co-doping with Tm3+ and Dy3+. White cathodoluminescence (CL) has been realized in a single-phase SrY2O4 host by co-doping with Tm3+ and Dy3+ for the first time with CIE (0.315, 0.333). Furthermore, the cathodoluminescence (CL) properties of SrY2O4: Tb3+/Tm3+/Dy3+ phosphors including the dependence of CL intensity on accelerating voltage and filament current, the decay behaviour of CL intensity under electron bombardment, and the stability of CIE chromaticity coordinate have been investigated in detail. The as-prepared phosphors might be promising for use in field-emission display (FED) devices.
TL;DR: In this article, an agglomerated peanut-like morphology was obtained and the monoclinic structure that is in good agreement with the standard NaSrBO 3 was confirmed by X-ray diffraction.
TL;DR: In this paper, an integrated electron energy loss spectroscopy, cathodoluminescence and electron beam induced current system has been designed and built to probe electrical and optical properties of individual defects.
TL;DR: Ammonothermal GaN growth using a novel apparatus has been performed on c-plane, m-plane and semipolar seed crystals with diameters between 5 mm and 2 in. as discussed by the authors.
Abstract: Ammonothermal GaN growth using a novel apparatus has been performed on c-plane, m-plane, and semipolar seed crystals with diameters between 5 mm and 2 in. to thicknesses of 0.5–3 mm. The highest growth rates are greater than 40 µm/h and rates in the 10–30 µm/h range are routinely observed for all orientations. These values are 5–100× larger than those achieved by conventional ammonothermal GaN growth. The crystals have been characterized by X-ray diffraction rocking-curve (XRC) analysis, optical and scanning electron microscopy (SEM), cathodoluminescence (CL), optical spectroscopy, and capacitance–voltage measurements. The crystallinity of the grown crystals is similar to or better than that of the seed crystals, with FWHM values of about 20–100 arcsec and dislocation densities of 1 ×105–5 ×106 cm-2. Dislocation densities below 104 cm-2 are observed in laterally-grown crystals. Epitaxial InGaN quantum well structures have been successfully grown on ammonothermal wafers.
TL;DR: In this paper, a room-temperature sharp ultraviolet (UV) lasing-like peak in various ZnS nanobelts was achieved, and the main UV luminescence peaks appeared at wavelengths between 330 and 338 nm.
Abstract: 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.
TL;DR: Heterojunction LEDs based on the well-aligned ZnO nanorods and nanotubes on the p-type GaN with the insertion of the NiO buffer layer that showed enhancement in the light emission.
Abstract: Cheap and efficient white light-emitting diodes (LEDs) are of great interest due to the energy crisis all over the world. Herein, we have developed heterojunction LEDs based on the well-aligned ZnO nanorods and nanotubes on the p-type GaN with the insertion of the NiO buffer layer that showed enhancement in the light emission. Scanning electron microscopy have well demonstrated the arrays of the ZnO nanorods and the proper etching into the nanotubes. X-ray diffraction study describes the wurtzite crystal structure array of ZnO nanorods with the involvement of GaN at the (002) peak. The cathodoluminescence spectra represent strong and broad visible emission peaks compared to the UV emission and a weak peak at 425 nm which is originated from GaN. Electroluminescence study has shown highly improved luminescence response for the LEDs fabricated with NiO buffer layer compared to that without NiO layer. Introducing a sandwich-thin layer of NiO between the n-type ZnO and the p-type GaN will possibly block the injection of electrons from the ZnO to the GaN. Moreover, the presence of NiO buffer layer might create the confinement effect.
TL;DR: This work predicts the existence of the Fano interference effect in the electron energy loss spectroscopy and cathodoluminescence of symmetry-broken nanorod dimers that are heterogeneous in material composition and asymmetric in length and introduces a new class of Fano interferences that are uniquely electron-driven and are absent in the optical response.
Abstract: Through numerical simulation, we predict the existence of the Fano interference effect in the electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) of symmetry-broken nanorod dimers that are heterogeneous in material composition and asymmetric in length. The differing selection rules of the electron probe in comparison to the photon of a plane wave allow for the simultaneous excitation of both optically bright and dark plasmons of each monomer unit, suggesting that Fano resonances will not arise in EELS and CL. Yet, interferences are manifested in the dimer’s scattered near- and far-fields and are evident in EELS and CL due to the rapid π-phase offset in the polarizations between super-radiant and subradiant hybridized plasmon modes of the dimer as a function of the energy loss suffered by the impinging electron. Depending upon the location of the electron beam, we demonstrate the conditions under which Fano interferences will be present in both optical and electron spectroscopies (EELS an...
TL;DR: In functional time-dependent photoresponsivity of photodetectors based on β-Ga₂O₃ epilayers, point defects contribution overcomes the contribution of crystallinity, however, the crystalline structure affects the intensities and emission regions of CL spectra more than point defects.
Abstract: This study evaluates the effect of crystallinity and point defects on time-dependent photoresponsivity and the cathodoluminescence (CL) properties of β-Ga₂O₃ epilayers. A synchrotron high-resolution X-ray technique was used to understand the crystalline structure of samples. Rutherford backscattering spectroscopy was used to determine the net chemical composition of the samples to examine the type and ratio of their possible point defects. The results show that in functional time-dependent photoresponsivity of photodetectors based on β-Ga₂O₃ epilayers, point defects contribution overcomes the contribution of crystallinity. However, the crystalline structure affects the intensities and emission regions of CL spectra more than point defects.
TL;DR: In this paper, top-down fabricated GaN nanowires were used to experimentally determine the evolution of strain along the vertical direction of 1-dimensional objects, and the elastic relaxation behavior derived from optical and structural characterizations perfectly matched the numerical results of calculations based on a continuous media approach.
Abstract: Top-down fabricated GaN nanowires, 250 nm in diameter and with various heights, have been used to experimentally determine the evolution of strain along the vertical direction of 1-dimensional objects. X-ray diffraction and photoluminescence techniques have been used to obtain the strain profile inside the nanowires from their base to their top facet for both initial compressive and tensile strains. The relaxation behaviors derived from optical and structural characterizations perfectly match the numerical results of calculations based on a continuous media approach. By monitoring the elastic relaxation enabled by the lateral free-surfaces, the height from which the nanowires can be considered strain-free has been estimated. Based on this result, NWs sufficiently high to be strain-free have been coalesced to form a continuous GaN layer. X-ray diffraction, photoluminescence, and cathodoluminescence clearly show that despite the initial strain-free nanowires template, the final GaN layer is strained.
TL;DR: In this paper, the fracto-mechanoluminescent (ML) spectra of noncentric and centric organic and inorganic crystals have been analyzed and a large number of them exhibit intrinsic and extrinsic ML due to the electron bombardment and electron-trapping mechanisms.
TL;DR: An improved Fe-catalyzed chemical vapour deposition method for synthesizing ultra-long α-Si3N4 nanobelts along with a few nanowires and nanobranches on a carbon felt substrate is reported, which would be useful in developing new photoelectric nanodevices with tailorable or tunable properties.
Abstract: Preparation of nanomaterials with various morphologies and exploiting their novel physical properties are of vital importance in nanoscientific field. Similarly to the III-N compound semiconductors, Si3N4 nanostructures also could be potentially used for making optoelectronic devices. In this paper, we report on an improved Fe-catalyzed chemical vapour deposition method for synthesizing ultra-long α-Si3N4 nanobelts along with a few nanowires and nanobranches on a carbon felt substrate. The ultra-long α-Si3N4 nanobelts grew via a combined VLS-base and nanobranches via a combined double-stage VLS-base and VS-tip mechanism, as well as nanowires via VLS-tip mechanism. The three individual nanostructures showed variant optical properties as revealed by a cathodoluminescence spectroscopy. A single α-Si3N4 nanobelt or nanobranch gave a strong UV-blue emission band as well as a broad red emission, whereas a single α-Si3N4 nanowire exhibited only a broad UV-blue emission. The results reported would be useful in developing new photoelectric nanodevices with tailorable or tunable properties.
TL;DR: Control experiments indicate that sodium citrate as a shape modifier introduced into the reaction system plays a critical role in the shape evolution of the final products, making these materials have potential applications in field-emission display devices.
Abstract: GdOF:Ln3+ (Ln = Eu, Tb, Tm, Dy, Ho and Sm) microspheres (1.5 μm) with high uniformity and monodispersity have been synthesized via a facile hydrothermal method followed by heat treatment (600 °C). X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), as well as photoluminescence (PL) and cathodoluminescence (CL) spectra are used to characterize the resulting samples. A series of controlled experiments indicate that sodium citrate (Cit3−) as a shape modifier introduced into the reaction system plays a critical role in the shape evolution of the final products. Furthermore, the shape and size of the products can be further manipulated by adjusting the dosage of Cit3− and pH values in the initial solution. The possible formation mechanism for these microspheres has been presented. Under UV light and low-voltage electron beam excitation, GdOF:Ln3+ microspheres show the characteristic f–f transitions of Ln3+ (Eu, Tb/Ho, Tm, Dy and Sm) ions and give bright red, green, blue, yellow and yellowish-orange emission, respectively. In addition, multicolored luminescence containing white emission have been successfully confected for co-doped GdOF:Ln3+ phosphors by changing the doped Ln3+ ions and adjusting their doping concentrations due to the simultaneous luminescence of Ln3+ in the GdOF host, making these materials have potential applications in field-emission display devices.
TL;DR: In this paper, the effect of dimensional confinement on the optical band gap of SrTiO3 is investigated by periodically introducing one extra SrO monolayer every n Sr TiO3 layers.
Abstract: The effect of dimensional confinement on the optical band gap of SrTiO3 is investigated by periodically introducing one extra SrO monolayer every n SrTiO3 layers. The result is the n = 1–5 and 10 members of the Srn+1TinO3n+1 Ruddlesden-Popper homologous series. Spectroscopic ellipsometry, optical transmission, and cathodoluminescence measurements reveal these Srn+1TinO3n+1 phases to have indirect optical band gaps at room temperature with values that decrease monotonically with increasing n. First-principles calculations suggest that as n increases and the TiO6 octahedra become connected for increasing distances along the c-axis, the band edge electronic states become less confined. This is responsible for the decrease in band gaps with increasing n (for finite n) among Srn+1TinO3n+1 phases.
TL;DR: In this article, the aragonite-calcite transformation temperature during heating is reviewed, in order to trace the chemical alteration of archaeological fired shells, and new data are presented for Mn2+ activated luminescence in crystalline vaterite.
Abstract: Cathodoluminescence (CL) microscopy is a powerful technique for studying biominerals. New progress on CL observation of biological materials is discussed especially the Mn2+ incorporation in shells during life and the relationship with environmental and/or diagenetic parameters. The aragonite-calcite transformation temperature during heating is reviewed, for example, in order to trace the chemical alteration of archaeological fired shells. New data are presented for Mn2+ activated luminescence in crystalline vaterite.
TL;DR: In this paper, α-Bi_2O-3 microcrystals and microrods with pyramidal tips have been grown by a vapour-solid method using pure Bi as starting material.
TL;DR: In this paper, the authors reported the red-emitting phosphors of trivalent europium (Eu3+) ions activated CaGd4O7 (CG) prepared by a sol-gel method.