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PL Spectra (pl + spectrum)
Selected AbstractsOptical properties of ZnO nanotubesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2010Hongju Zhai Abstract Tubular ZnO nanostructures have been obtained via a hydrothermal method at low temperature (90 °C) without any catalysts or templates. The XRD measurement reveals that the tubes are single crystals with hexagonal wurtzite structure. SEM shows that the diameters of ZnO nanotubes ranged from 400 to 550 nm. The Raman and PL spectra indicate that oxygen vacancies or Zn interstitials are responsible for the green emission in the ZnO nanotubes. A possible growth mechanism on the formation of crystalline ZnO nanotubes has been presented. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Silica Supported Submicron SiO2@Y2SiO5:Eu3+ and SiO2@Y2SiO5:Ce3+/Tb3+ Spherical Particles with a Core,Shell Structure: Sol,Gel Synthesis and CharacterizationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2006Cuikun Lin Abstract X1 -Y2SiO5:Eu3+ and X1 -Y2SiO5:Ce3+ and/or Tb3+ phosphor layers have been coated on nonaggregated, monodisperse, submicron spherical SiO2 particles by a sol,gel process, followed by surface reaction at high temperature (1000 °C), to give core/shell structured SiO2@Y2SiO5:Eu3+ and SiO2@Y2SiO5:Ce3+/Tb3+ particles. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), TEM, photoluminescence (PL), low voltage cathodoluminescence (CL), and time-resolved PL spectra and lifetimes are used to characterize these materials. The XRD results indicate that X1 -Y2SiO5 layers have been successfully coated on the surface of SiO2 particles, as further verified by the FESEM and TEM images. The PL and CL studies suggest that SiO2@Y2SiO5:Eu3+, SiO2@Y2SiO5:Tb3+ (or Ce3+/Tb3+), and SiO2@Y2SiO5:Ce3+ core/shell particles exhibit red (Eu3+, 613 nm: 5D0,7F2), green (Tb3+, 542 nm: 5D4,7F5), or blue (Ce3+, 450 nm: 5d-4f) luminescence, respectively. PL excitation, emission, and time-resolved spectra demonstrate that there is an energy transfer from Ce3+ to Tb3+ in the SiO2@Y2SiO5:Ce3+,Tb3+ core/shell particles. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Light-Emitting Rubrene Nanowire Arrays: A Comparison with Rubrene Single CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Jin Woo Lee Abstract This is a report on a new method of growth of a light-emitting rubrene nanowires array with diameters of 200,±,10,nm by using organic vapor transport through Al2O3 nanoporous templates. Nanometer-scale laser confocal microscope (LCM) photoluminescence (PL) spectra and crystalline structures of the rubrene nanowires are compared with those of rubrene single crystals prepared with the same experimental conditions without the template. In the LCM PL spectra it is observed that the PL spectra and intensity varies with the detecting positions because of the crystal growth characteristics of the rubrene molecules. A single rubrene nanowire has a wider LCM PL band width than that of the rubrene single crystal. This may originate from the light emissions of the mixed polarized bands due to additional new crystallinity in the formation of the nanowires. From the current,voltage characteristic curves, the semiconducting nature of both the rubrene nanowires and single crystals is observed. [source] Stable Blue Emission from a Polyfluorene/Layered-Compound Guest/Host Nanocomposite,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2006E. Aharon Abstract In this study a blue-light-emitting conjugated polymer, poly(9,9-dioctylfluorene), is confined to the interlayer space of inorganic, layered metal dichalcogenide materials, metallic MoS2, and semiconducting SnS2. The nanocomposites are prepared through Li intercalation into the inorganic compound, exfoliation, and restacking in the presence of the polymer. X-ray diffraction and optical absorption measurements indicate that a single conjugated polymer monolayer, with an overall extended planar morphology conformation, is isolated between the inorganic sheets, so that polymer aggregation or ,,, interchain interactions are significantly reduced. Photoluminescence (PL) measurements show that the appearance of the undesirable green emission observed in pristine polymer films is suppressed by incorporating the polymer into the inorganic matrix. The blue emission of the intercalated polymer is stable for extended periods of time, over two years, under ambient conditions. Furthermore, the green emission is absent in the PL spectra of nanocomposite films heated at 100,°C for 7,h in air with direct excitation of the keto defect. Finally, no green emission was observed in the electroluminescence spectrum of light-emitting devices fabricated with a polymer-intercalated SnS2 nanocomposite film. These results support the proposed hypothesis that fluorenone defects alone are insufficient to generate the green emission and that interchain interactions are also required. [source] Composition- and Shape-Controlled Synthesis and Optical Properties of ZnxCd1,xS Alloyed Nanocrystals,ADVANCED FUNCTIONAL MATERIALS, Issue 3 2005C. Li Abstract Composition-tunable ZnxCd1,xS alloyed nanocrystals have been synthesized by a new approach consisting of thermolyzing a mixture of cadmium ethylxanthate (Cd(exan)2) and zinc ethylxanthate (Zn(exan)2) precursors in hot, coordinating solvents at relatively low temperatures (180,210,°C). The composition of the alloyed nanocrystals was accurately adjusted by controlling the molar ratio of Cd(exan)2 to Zn(exan)2 in the mixed reactants. The alloyed ZnxCd1,xS nanocrystals prepared in HDA/TOP (HDA: hexadecylamine; TOP: trioctylphosphine) solution exhibit composition-dependent shape and phase structures as well as composition-dependent optical properties. The shape of the ZnxCd1,xS nanocrystals changed from dot to single-armed rod then to multi-armed rod with a decrease of Zn content in the ternary nanoparticles. The alloying nature of the ZnxCd1,xS nanocrystals was consistently confirmed by the results of high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and UV-vis absorption and photoluminescence (PL) spectroscopy. Further, the shape-controlled synthesis of the ternary alloyed nanocrystals was realized by selecting appropriate solvents. Uniform nanodots in the whole composition range were obtained from TOPO/TOP solution, (TOPO: trioctylphosphine oxide) and uniform nanorods in the whole composition range were prepared from HDA/OA solution (OA: octylamine). The effect of the reaction conditions, such as solvent, reaction temperature, and reaction time, on the PL spectra of the alloyed ZnxCd1,xS nanocrystals was also systematically studied, and the reaction conditions were optimized for improving the PL properties of the nanocrystals. [source] Synthesis of imidazole-containing conjugated polymers bearing phenol unit as side group and excited state intramolecular proton transfer-mediated fluorescenceJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2009Koji Takagi Abstract Dibromobenzimidazole and dibromoimidazole bearing hydroxyl group-protected phenol unit (1 and 2) were prepared and they showed an intramolecular hydrogen bonding between ether oxygen and amino proton of imidazole. The palladium-catalyzed Suzuki coupling polymerization of 1 and 2 with benzene bis(boronic acid) derivatives gave soluble polymers (3 and 4), where the molecular weights were limited probably due to the coordination ability of imidazole to palladium metal. The phenol hydroxyl groups were subsequently deprotected using BBr3 to obtain 3, and 4,. From the 1H NMR spectra, the complete conversion to the hydroxyl group and the formation of another type of intramolecular hydrogen bonding between hydroxyl proton and imine nitrogen were confirmed. In the UV and PL spectra of 3, and 4,, the excited state intramolecular proton transfer (ESIPT) occurred to shift the emission spectra toward lower energy region compared to 3 and 4. Especially, the PL spectrum of 3, demonstrated large stokes shift (145 nm) in THF solution. The ESIPT-mediated fluorescence was influenced by the addition of methanol and trifluoroacetic acid, which inhibited the formation of intramolecular hydrogen bonding. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4822,4829, 2009 [source] Carbazolevinylene-based polymers and model compounds with oxadiazole and triphenylamine segments: Synthesis, photophysics, and electroluminescenceJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2008Panagiotis D. Vellis Abstract Two new soluble alternating carbazolevinylene-based polymers POXD and PTPA as well as the corresponding model compounds MOXD and MTPA were synthesized by Heck coupling. POXD and MOXD contained 2,5-diphenyloxadiazole segments, while PTPA and MTPA contained triphenylamine segments. All samples displayed high thermal stability. The polymers had higher glass transition temperature (Tg) than their corresponding model compounds. The samples showed absorption maximum at 364,403 nm with optical band gap of 2.62,2.82 eV. They emitted blue-green light with photoluminescence (PL) emission maximum at 450,501 nm and PL quantum yields in THF solution of 0.15,0.36. The absorption and the PL emission maxima of PTPA and MTPA were blue-shifted as compared to those of POXD and MOXD. The electroluminescence (EL) spectra of multilayered devices made using four materials exhibited bluish green emissions, which is well consistent with PL spectra. The EL devices made using poly(vinyl carbazole) doped with MOXD and MTPA as emitting materials showed luminances of 12.1 and 4.8 cd m,2. POXD and PTPA exhibited 25.4, and 96.3 cd m,2, respectively. The polymer containing the corresponding molecules in the repeating group showed much higher device performances. Additionally, POXD and MOXD exhibited better stability of external quantum efficiency (EQE) and luminous efficiency with current density resulting from enhancing the electron transporting properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5592,5603, 2008 [source] Host copolymers containing pendant carbazole and oxadiazole groups: Synthesis, characterization and optoelectronic applications for efficient green phosphorescent OLEDsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2008Kun-Ming Yeh Abstract Vinyl copolymers (PCOn), containing pendant carbazole and aromatic 1,3,4-oxadiazole attached with dodecyloxy group, were prepared from their corresponding precursor poly(9-vinyl carbazole- co -4-vinylbenzyl chloride) (PCBn) by the Williamson condensation (n: mole% of 4-vinylbenzyl chloride). These copolymers were used as host materials for green phosphorescent light-emitting diodes after blending 4 wt % of Ir(ppy)3. PL spectra of the PCOn films showed the formation of excimer or exciplex. The phosphorescent EL devices were fabricated with a configuration of ITO/PEDOT:PSS/host copolymers:Ir(ppy)3/BCP/Ca/Al. The PL and EL spectra of the blends [PCOn:Ir(ppy)3] revealed dominant green emission at 517 nm attributed to Ir(ppy)3 due to efficient energy transfer from the host to Ir(ppy)3. Efficient green phosphorescent OLEDs was obtained when employing copolymer PCO16 as the host and Ir(ppy)3 as the guest. The maximal luminance efficiency and the maximal luminance of this device were 17.9 cd/A and 19,903 cd/m2, respectively. After doped with Ir(ppy)3, the morphology of the films, both controlled PCO20 and PCO20 with attached dodecyloxy groups, were investigated by tapping-mode AFM and FE-SEM. The film of PCO20 exhibited uniform, featureless image and showed much better device performance than PCO20, which have been attributed to good compatibility of PCO20 with Ir(ppy)3. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5180,5193, 2008 [source] Synthesis and characterization of novel germanium-containing poly(p -phenylenevinylene) derivativesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2008Hoon-Je Cho Abstract Novel blue-emitting germanium-containing poly(p -phenylenevinylene) (PPV) derivatives with well-defined conjugation lengths were synthesized via Wittig-condensation polymerizations. The polymers can be color-tuned by the introduction of various chromophores into the PPV-based polymer backbones. The photoluminescence (PL) spectra of the polymers, GePVK (containing carbazole moieties), GeMEH (containing dialkoxybenzene moieties), and GePTH (containing phenothiazine moieties), were found to exhibit blue, greenish blue, and green emissions, respectively. GePTH produces more red-shifted emission than GeMEH and GEPVK, resulting in green emission, and the solution and solid state PL spectra of GePVK consist of almost blue emission. The electroluminescence spectra of GeMEH and GePTH contain yellowy green and yellow colors, respectively. Interestingly, GePVK exhibits white emission with CIE coordinates of (0.33, 0.37) due to electroplex emission in the light-emitting diodes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 979,988, 2008 [source] Synthesis and Light-Emitting Properties of New Polyimides Containing Ethynylene Units in the Main ChainMACROMOLECULAR MATERIALS & ENGINEERING, Issue 7 2007Jun Ho Chi Abstract Two new polyimides (ODA-PI and HDA-PI) having 1,4-phenylenediethynylene unit and octyloxy groups were synthesized. Judging from inherent viscosities of their precursor PAAs (1.42 and 1.62 dL,·,g,1), the two PIs were very high in molecular weight. Casting and thermal imidization of PAAs results polyimides with good-quality films. They were stable up to 364,°C and showed no crystallites. UV-vis and PL spectra in NMP solutions of both PIs showed maxima at 442 and 501 nm, respectively, while PL spectra in ,10 µm thick films exhibited a maximum at 540 nm. CV indicates that two PIs were electrochemically active in redox region. The devices with construction of ITO/PEDOT/PIs/BAlq3/LiF/Al exhibited turn-on voltages of 6.5 V in ODA-PI and 7.5 V in HDA-PI and emitted a bright bluish-green light. ODA-PI and HDA-PI showed maximum luminescence of 256 and 316 cd,·,cm,2, respectively, at the same voltage of 12 V. [source] Photoluminescence properties of GaAs nanowire ensembles with zincblende and wurtzite crystal structurePHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 7 2010B. V. Novikov Abstract Self-standing III,V nanowires (NWs) are promising building blocks for future optoelectronic devices such as LEDs, lasers, photodetectors and solar cells. In this work, we present the results of low temperature photoluminescence (PL) characterization of GaAs NWs grown by Au-assisted molecular beam epitaxy (MBE), coupled with the transmission electron microscopy (TEM) structural analysis. PL spectra contain exci- ton peaks from zincblende (ZB) and wurtzite (WZ) crystal structures of GaAs. The peaks are influenced by the quantum confinement effects. PL bands corresponding to the exciton emission from ZB and WZ crystal phases are identified, relating to the PL peaks at 1.519 eV and 1.478 eV, respectively. The obtained red shift of 41 meV for WZ GaAs should persist in thin NWs as well as in bulk materials. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Energy transfer from rare-earth element to Mn in (Ca,Sr)Ga2S4 compoundsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2009Toshimitsu Obonai Abstract For realizing a red-colour emission using SrGa2S4 compounds, Mn and rare-earth-element (REE) co-doping is tried. Photoluminescence (PL) and photoluminescence excitation (PLE) spectra are measured using samples so prepared. As a result, enhancement of the Mn red emission is observed. Considering the 4f and 5d levels of REE in the host material, it is expected that the energy transfer from REE to Mn is caused by the weak coupling between the d levels of REE and Mn. Moreover, in the Ce co-doping case, another process is expected as a resonant energy transfer between the 4f,5d transition of Ce3+ and a certain transition of Mn2+. To specify the Mn2+ levels related to the resonant transfer, PL spectra of a Mn only doped CaGa2S4 single crystal and an undoped one are measured at low temperatures, though we could not find emission expected to be related to the resonant transfer. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoluminescence and Hall studies of GaN:Fe and (Ga,Fe)N:Mg layersPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2007M. Wegscheider Abstract Temperature dependent photoluminescence (PL) in the ultraviolet (UV) regime and Hall measurements at room temperature have been performed on Metal-Organic-Chemical-Vapour-Deposition (MOCVD) grown GaN:Fe and (Ga,Fe)N:Mg layers. PL measurements were employed in order to study the dopants' influence on the near-band edge excitonic emission and their tendency to provoke the formation and suppression of defects or incorporation of impurities. For their identification and for the understanding of the PL spectra the evaluation of the free carrier concentrations via Hall measurements were necessary. Depending on the iron concentration of the (Ga,Fe)N layers, the near-band edge emission goes through two different stages: at low Fe-concentration no excitonic emission can be seen whereas with higher doping levels, excitonic features develop. The (Ga,Fe)N films exhibit n-type behaviour. The Mg codoped samples show strong Mg and defect related luminescence bands, whose occurrence and intensity also strongly depends on whether high or low Fe concentration is present. The (Ga,Fe)N:Mg layers were semi insulating. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoluminescence of Hg-doped CdS nanowiresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2006Shao-Min Zhou Abstract Hg-doped CdS nanowires with an average diameter of ,10,15 nm and lengths up to hundreds of micrometers are fabricated by chemical vapor reaction. The as-synthesized products have a single crystal phase and grow along the ,001, direction. The growth of Hg-doped CdS nanowires is suggested for the quasi-vapor,solid mechanism (QVSM). In particular, the PL spectra show enhancing emission peaks that strongly shift to long wavelengths (up to 115 nm redshift) with Hg doping where the Hg-doped CdS nanowires are found to be responsible for the different characteristics; the PL mechanism is explained in detail. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical characterization of Zn0.97Mn0.03Se/ZnSe0.92Te0.08 type II multiple-quantum-well structuresPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2007D. Y. Lin Abstract The optical characterization of type II Zn0.97Mn0.03Se/ZnSe0.92Te0.08 multiple-quantum-well structures have been studied using photoluminescence (PL), temperature-dependent PL, polarized PL, power-dependent PL, and photoreflectance (PR) in this study. The PL data reveal that the band alignment of the ZnMnSe/ZnSeTe system is type II. Comparing with the theoretical calculation based on the Schrodinger equation, the valence band offset is estimated to be 0.6 eV. From the power-dependent PL spectra, it is observed that the peak position of PL spectra shows a blueshift under different excitation power. The blueshift can be interpreted in terms of the band-bending effect due to spatially photoexcited carriers in a type II alignment. The thermal activation energy (EA) for quenching the PL intensity was determined from tem- perature-dependent PL spectra. The thermal activation energy was found to decrease as the thickness of ZnMnSe and ZnSeTe layers decreased. The polarized PL spectra exhibit a large in-plane polarization with the polarization degree up to 50%. The polarization does not depend on the excitation intensity as well as temperature. The large polarization is an inherent orientation of the interface chemical bonds. The higher transition features observed in PR spectra show a blueshift with the similar trend observed in the PL spectra as decreasing the thickness of ZnSeTe layer. This result provides a consistent evidence for the assumption that square-like well shapes were built in the ZnSeTe layers. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoluminescence microscopy of as-grown individual single-walled carbon nanotubes on Si/SiO2 substratesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006Oliver Kiowski Abstract We present far-field photoluminescence (PL) imaging at room temperature of tens of micrometer long individual single-walled carbon nanotubes (SWNTs) grown and measured directly on a Si/SiO2 surface. The SWNTs are grown by Chemical Vapour Deposition (CVD) with ethanol as carbon source and contact the surface with their full length. We detect the PL and its variations along SWNTs in a home-built laser microscope with a spatial resolution of ,400 nm. We are able to reliably assign (n, m)-structure of SWNTs by measuring PL spectra in the range of 800,1600 nm as function of the excitation wavelength varying between 710 and 860 nm. This allows us to check structural integrity (changes of helicity) along the tube. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Reflectance and photoluminescence studies of InGaN/GaN multiple-quantum-well structures embedded in an asymmetric microcavityPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2006D. Y. Lin Abstract Using reflectance (R) and photoluminescence (PL) measurements InGaN/GaN multiple-quantum-well (MQW) structures embedded in an asymmetric microcavity with different thickness of stacking pairs have been studied. The asymmetric microcavity structures are composed of a cavity sandwitched between the air/semiconductor interface and a mirror using distributed Bragg reflector (DBR). For the DBR with thinner AlN layers the high-reflectivity stop band locates at higher photon energy. The luminescence efficiency and the spectrum of InGaN/GaN multiple-quantum-well structures will be modified by the microcavity. A comparison of PL with R spectra shows that the emission efficiency can be enhanced by matching up the luminescence spectrum coming from the MQW and the high-reflectivity stop band. From the blue shift of the cavity modes as a function of incident angles the refractive index and cavity length can be determined. By measuring the PL spectra as a function of emission angle, it is found that the PL spectra were predominatly determined by microcavity resonances. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Manifestation of the equilibrium hole distribution in photoluminescence of n-InNPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2005A. A. Klochikhin Abstract Photoluminescence (PL) of n-InN grown by molecular beam epitaxy with Hall concentrations from 3.6 to 7.3 × 1017 cm,3 demonstrates dependences on carrier concentration, temperature, and excitation density which give evidences of a fast energy relaxation rate of photoholes and their equilibrium distribution over localized states. The structure of the PL spectra observed at 4.2 and 77 K in the energy interval from 0.50 to 0.67 eV indicates that a considerable part of holes is trapped by deep and shallow acceptors before the interband recombi- nation with degenerate electrons occurs. At room temperature, the band-to-band recombination of free holes and electrons dominates in PL. Experimental results on PL and absorption are described by model calculations under the assumptions of a band gap equal to 0.665,0.670 eV at zero temperature and zero carrier concentration and a non-parabolic conduction band with the effective mass at the G -point equal to 0.07 of the free electron mass. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Stranski,Krastanow growth of stacked GaN quantum dots with intense photoluminescencePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003K. Hoshino Abstract Multiple-layer stacked GaN quantum dots (QDs) with intense photoluminescence (PL) have been grown by the Stranski,Krastanow growth mode in metalorganic chemical vapor deposition. Scanning transmission electron microscopy (STEM) analysis shows that the vertical aligned QDs are formed, which results from a strain field induced by buried islands. We have also investigated PL spectra at room temperature. The PL intensity increases with increasing number of the stacked layer. This indicates that the carriers can be injected into each layer of GaN quantum dots. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical and magnetic properties of the DyN/GaN superlatticePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003Y. K. Zhou Abstract Ferromagnet/semiconductor DyN/GaN superlattice structures were grown on SiC substrate by radio frequency molecular beam epitaxy. Formation of DyN was confirmed by X-ray diffraction measurements. The temperature dependence of the photoluminescence (PL) spectra for the DyN/GaN superlattice and GaDyN samples was studied. Sharp PL peaks from two samples showed no shift with temperature, indicating the intra-atomic f,f transition at Dy ions. Comparison of the PL spectra for the DyN/GaN superlattice and GaDyN suggests that GaDyN is formed at the GaN/DyN interface. The DyN/GaN superlattice exhibited two ferromagnetic components; one is major at low temperatures (<50 K) and the other is major at high temperatures (>350 K). The former shows large coercivity Hc of about 1800 Oe at 7 K, which was originated from DyN layers. The latter may come from GaDyN, which was formed at the GaN/DyN interface. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Metallic nanoparticle array on GaN by microsphere lithographyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Giuseppe Y. Mak Abstract The optical characteristics of GaN blue-light (peak wavelength at 440 nm) light-emitting diode (LED) under the effect of localized surface plasmon (LSP) have been studied. Hexagonal arrays of triangular metallic nanoparticles deposited through a self-assembled silica microsphere mask have been fabricated using vertical deposition. By comparing the PL spectra of samples coated with Au, Al and Ag nanoparticles, it is found that Ag nanoparticles offer the most pronounced PL enhancement. The resonance wavelength was determined from optical transmission and verified by theoretical calculations. These results provide a cost-effective solution for improving the efficiency of LEDs. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Trap state emission of water-soluble CdS nanocrystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009W. Lü Abstract We prepared water-soluble CdS nanocrystals (NCs) capped by the poly (ethylene glycol)-b-poly (2-(N,N -dimethylamino)ethyl methacrylate) chain. The photoluminescence (PL) properties of CdS NCs are investigated by time-resolved and temperature-dependent PL spectra. It is found that the PL band of CdS NCs is dominated by two trap state emissions, respectively. Due to the trap state emissions, fluorescent resonance energy transfer from CdS NCs to organic dyes (Texasred) can be observed, which suggests the potential application of trap states of CdS NCs for fabrication of biosensors. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Luminescence and energy structure of ultrathin InAs/AlAs quantum wellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2008T. S. Shamirzaev Abstract The energy spectrum of thin InAs/AlAs quantum wells (QWs) has been studied by photoluminescence (PL). It has been found that the PL spectra of the QWs consist of intense lines related to a no-phonon excitonic transition accompanied with its phonon replicas. The band alignment in the QWs with the lowest conduction band states belonging to the indirect minimum is shown to be of type I. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pulsed layer growth of AlInGaN nanostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008Michael Jetter Abstract A pulsed layer growth mode in the metal-organic vapor phase epitaxy (MOVPE) was used to fabricate excellent quality AlInGaN nanostructures. The amount of material was varied, resulting in AlInGaN layer thicknesses between nominally 1.5 nm and 6 nm, respectively. We have analyzed the material properties by X-ray diffraction (XRD) as well as photoluminescence (PL) spectroscopy. The observed XRD-spectra and the PL intensity show the high quality of the deposited material. By analyzing the PL spectra we have found an energetic shift of the resonance lines from 2.65 eV to 3.33 eV with decreasing well thickness. We attribute this shift mainly to the presence of internal electric fields at the AlIn-GaN/GaN interface. Power-dependent and time resolved PL experiments confirm this observation. Comparing the luminescence at elevated temperatures, the pulsed layer epitaxy structures reveal a much higher intensity as the conventional grown samples. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoluminescence spectroscopy and transport electrical measurements reveal the quantized features of Si nanocrystals embedded in an ultra thin SiO2 layerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007C. Dumas Abstract In this paper, we have investigated the quantized charging features revealed by nanometer scale devices containing a 2D array of Si nanoparticles (nps) embedded into a SiO2 layer. The Si nps were synthesized by ultra low energy ion implantation and annealing under slightly oxidizing ambient. The structural characteristics of the material (oxide thicknesses, nps size and density) have been studied by Transmission Electron Microscopy (TEM) and Energy Filtered TEM (EFTEM). Moreover, photoluminescence (PL) spectroscopy and electrical I(V) measurements using a MOS capacitor addressing only a few nps have been performed at room temperature. It is observed that, as the oxidizing annealing temperature increases, the nps size decreases and the oxide quality is restored. These features appear on the PL spectra as a blue shift of the PL red band linked to quantum confinement into nps and on the I(V) characteristics as an increase of the voltage peak width and a decrease of the main current background. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Time-resolved photoluminescence and steady-state optical studies of GaInNAs and GaInAs single quantum wellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007Y. Sun Abstract Time-resolved photoluminescence spectroscopy is used to investigate carrier dynamics of Ga1,xInxNyAs1,y (x , 0.33, y , 0.01) single quantum well (QW) structures. PL spectra measured as a function of temperature together with the PL decay times at wavelengths around and below the PL peak energy are used to determine de-trapping activation energies and time constants. The results are interpreted in terms of simultaneous thermal excitation of deep localized excitons to shallow localized states. According to the model, with increasing temperatures, localized excitons gain enough thermal energy to populate the free exciton states in quantum well with shorter lifetimes due to coherent nature of free excitons. In addition, at temperatures around and above 80 K, more non-radiative channels become available to compete with the radiative processes leading to shorter time constants. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural and optical properties of polycrystalline MgxZn1,xO and ZnO:Mn films prepared by chemical spray pyrolysisPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006Tomoaki Terasako Abstract Polycrystalline MgxZn1,xO (0.00 , x , 0.21) and ZnO:Mn films prepared by chemical spray pyrolysis were characterized by X-ray diffraction, optical transmittance, photoacoustic (PA) spectroscopy and photoluminescence (PL). Successful growth of the MgxZn1,xO (0.00 , x , 0.21) films was confirmed by the blue shift of both the near-band-edge PL peak and absorption edge with increasing the alloy composition x. However, the influence of the tail states caused by the deviation from stoichiometric compsosition and/or the spatial fluctuation of the alloy composition x was observed on the PA and PL spectra. Both the transmittance and PA spectra for the ZnO:Mn films showed the absorption band due to the d-d transitions in Mn2+ ion. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characterization of MBE grown ZnO on GaAs(111) substratesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006Takashi Matsumoto Abstract ZnO epitaxial layers grown on GaAs(111)B substrates by plasma assisted MBE with different O/Zn flux ratios are characterized by photoluminescence (PL), X-ray diffraction (XRD) , ,2, scan, , scan, and reciprocal lattice mapping. Low temperature PL spectra are dominated by bound exciton bands at 3.360 eV and 3.330 eV. The 3.360 eV band is strong in samples grown under Zn-rich cindition and the 3.330 eV band is strong in samples grown under O-rich condition. The epitaxial orientation relationship is ZnO(0001)//GaAs(111) and ZnO[11-20]//GaAs [01-1] irrespective of the O/Zn flux ratio. The ZnO c-axis tilts by 0.2° , 0.3° from the GaAs [111] axis toward ,1-10, or ,2-1-1, direction. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoluminescence properties of ZnO single crystals with polar and non-polar facesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006H. Sasaki Abstract Photoluminescence (PL) was circumstantially measured for ZnO single crystals with polar and non-polar faces. PL spectra of ZnO single crystals depended on the sector and polarity of ZnO single crystals. Emissions due to excitons from c -plane substrates sliced from the +c sector were strong, and FWHMs of the emissions were smaller than those from substrates sliced from the ,c sector. An emission due to neutral-donor-bound exicitons (D0X) at 3.361 eV was dominantly observed on all surfaces of ZnO single crystals, and an emission due to ionized-donor-bound excitons (D+X) around 3.366 eV was observed on the O-face but not on the Zn-face at 4.2 K. It is thought that surface state densities due to oxygen caused this difference in PL emission for polarity of ZnO. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vertical Bridgman growth and annealing effect of Bi doped ZnSe single crystalPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2004C. B. Oh Abstract In order to prepare p-type ZnSe, bismuth (Bi) as an acceptor dopant was doped into ZnSe single crystal by vertical Bridgman method. Photoluminescence (PL) spectra measured at 4.2 K on as-grown crystal showed the strong shallow donor,acceptor pair (DsAP) emission, deep donor,acceptor pair (DdAP) emission and weak I1Bi emission line. To enhance the activation ratio of Bi in ZnSe single crystals, ZnSe:Bi was annealed in saturated zinc and selenium atmosphere at different temperatures. In the case of annealing in the range of 700,800 °C, DdAP emission disappeared and the intensities of DsAP and I1Bi emission relatively increased. From the dependence of PL spectra on excitation light intensity and the temperature, the acceptor activation energy and deep donor level were estimated about 103 meV and 34 meV, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||