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Photoluminescence Spectroscopy (photoluminescence + spectroscopy)
Selected AbstractsFine structure of emission lines from charged CdSe/ZnSe/ZnMnSe quantum dotsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2010E. A. Chekhovich Abstract Photoluminescence spectroscopy has been employed to study CdSe/ZnSe/ZnMnSe quantum dots. For most of the dots studied here luminescence comes in three spectrally separated features: neutral exciton (X), biexciton (XX), and charged exciton (XC) states. Spectral properties of X and XX emission are well understood, however, in a marked contrast with previous studies, the observed fine structure of XC can not be explained within a commonly accepted model of a ground state trion luminescence. We find that at zero magnetic field luminescence from the charged state exhibits fine structure that varies gradually between different dots from a single unpolarized line to a quartet with the maximum splitting of 2,meV. Several models including magnetic polaron formation and double charging have been considered, but a plausible explanation can be given only if one considers the influence of a charge trapped in a nearby dot. [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] Synthesis of highly luminescent organoboron polymers connected by bifunctional 8-aminoquinolate linkersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2010Yuichiro Tokoro Abstract New organoboron aminoquinolate-based polymers linked by ,-conjugated bridge were prepared by Sonogashira,Hagihara coupling of organoboron aminoquinolate-based bisiodo monomers bearing biphenyl or bithiophene moiety with 1,4-diethynylbenzene derivatives. Tetracoordination states of boron atoms in the obtained polymers were confirmed by 11B NMR spectroscopy, and they were also characterized by 1H NMR and IR spectroscopies and size-exclusion chromatography. Their optical properties were studied by UV,vis absorption and photoluminescence spectroscopies. In the region above 400 nm, the polymers prepared from 1,4-diethynyl-2,5-dioctyloxybenzene showed bathochromic shifts when compared with those prepared from 1.4-diethynyl-2-perfluorooctyl-5-trifluoromethylbenzene. The polymers with biphenyl moiety showed higher absolute fluorescence quantum yields (,F = 0.28 and 0.65), whereas those with bithiophene moiety led to decreasing of the low quantum yields (,F = 0.19 and 0.00). The density-functional theory (DFT) and time-dependent,DFT calculations of model compounds corresponding to the polymers were in good agreement with the results from UV,vis properties. The calculations revealed that the electronic structure of the polymer with bithiophene moiety is different from that with biphenyl moiety, and predicted the electron transfer from the bithiophene moiety to the ,-extended quinoline moiety in transition state. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3693,3701, 2010 [source] Energy Transfer Enables 1.53 ,m Photoluminescence from Erbium-Doped TiO2 Semiconductor Nanocrystals Synthesized by Ar/O2 Radio-Frequency Thermal PlasmaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2008Ji-Guang Li Highly crystalline, highly luminescent nanopowders of Er3+ -doped TiO2 have been successfully synthesized via one-step Ar/O2 radio-frequency thermal plasma processing. Energy transfer from the TiO2 host to Er3+ activators has been confirmed by combined means of UV-vis, excitation, and photoluminescence spectroscopies. As a consequence, bright photoluminescence at ,1.53 ,m was observed from the nanopowders either by directly exciting the Er3+ activator or by exciting the TiO2 host lattice. A comparative study shows that the nanopowder of the same system made via coprecipitation lacks the energy transfer. The plasma-generated nanopowders may thus find applications in optoelectronic devices. [source] Oxygen induced band-gap reduction in ZnOxSe1,x alloysPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2004W. Shan Abstract The effect of alloying a small amount of ZnO with ZnSe on the electronic band structure has been studied. Optical transitions in MBE-grown ZnOxSe1,x epitaxial films (0 , x , 0.0135) were investigated using photoreflectance and photoluminescence spectroscopies. The fundamental band-gap energy of the alloys was found to decrease at a rate of about 0.1 eV per atomic percent of oxygen. The pressure dependence of the band gap was also found to be strongly affected by the O incorporation. Both effects can be quantitatively explained by an anticrossing interaction between the extended states of the conduction band of ZnSe and the highly localized oxygen states located at approximately 0.22 eV above the conduction band edge. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Luminescent chiral organoboron 8-aminoquinolate-coordination polymersAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 8 2010Yuichiro Tokoro Abstract We have successfully synthesized optically active organoboron aminoquinolate-based coordination polymers bearing the chiral side chain derived from L -alanine, and studied their optical behavior by UV,vis and photoluminescence spectroscopies. Higher absolute quantum yields (,F) of the obtained polymers, measured by integrating sphere method, were observed with electron-withdrawing substituent (,F = 0.80) than with electron-donating substituent (,F = 0.52). The circular dichroism (CD) study in the mixed solvents of CHCl3 and DMF showed that the secondary structures of the obtained polymers were stabilized by hydrogen-bonding interaction in the side chain. From concentration dependence on the CD spectra, the chirality of the obtained polymers originated from the nature of one molecule. Copyright © 2009 John Wiley & Sons, Ltd. [source] Solubilization of Single-Walled Carbon Nanotubes by using Polycyclic Aromatic Ammonium Amphiphiles in Water,Strategy for the Design of High-Performance SolubilizersCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2006Yasuhiko Tomonari Abstract We describe the design of polycyclic aromatic compounds with high performance that dissolve single-walled carbon nanotubes (SWNTs). Synthetic amphiphiles trimethyl-(2-oxo-2-phenylethyl)-ammonium bromide (1) and trimethyl-(2-naphthalen-2-yl-2-oxo-ethyl)-ammonium bromide (2) carrying a phenyl or a naphtyl moiety were not able to dissolve/disperse SWNTs in water. By contrast, trimethyl-(2-oxo-2-phenanthren-9-yl-ethyl)-ammonium bromide (3) solubilized SWNTs, although the solubilization ability was lower than that of trimethyl-(2-oxo-2-pyrene-1-yl-ethyl)-ammonium bromide (4) (solubilization behavior observed by using 4 was described briefly in reference 4a). Transmission electron microscopy (TEM), as well as visible/near-IR, fluorescence, and near-IR photoluminescence spectroscopies were employed to reveal the solubilization properties of 4 in water, and to compare these results with those obtained by using sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium bromide (HTAB) as solubilizers. Compound 4 solubilized both the as-produced SWNTs (raw-SWNTs) and purified SWNTs under mild experimental conditions, and the solubilization ability was better than that of SDS and HTAB. Near-IR photoluminescence measurements revealed that the chiral indices of the SWNTs dissolved in an aqueous solution of 4 were quite different from those obtained by using micelles of SDS and HTAB; for a SWNTs/4 solution, the intensity of the (7,6), (9,5), and (12,1) indices were strong and the chirality distribution was narrower than those of the micellar solutions. This indicates that the aqueous solution of 4 has a tendency to dissolve semiconducting SWNTs with diameters in the range of 0.89,1.0 nm, which are larger than those SWNTs (0.76,0.97 nm) dissolved in the aqueous micelles of SDS and HTAB. [source] Synthesis and Characterization of Single-Crystalline Lanthanum Fluoride with a Ring-Like NanostructureEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2009Yang Tian Abstract LaF3 ring-like nanostructures with a diameter of less than 2 ,m have been fabricated by a facile, effective, and environmentally friendly molten salt synthesis route in which NaNO3 and KNO3 (2:1 molar ratio) act as reaction media and the rare-earth nitrate and NaF as precursor. X-ray diffraction, TEM, HR-TEM, energy dispersive X-ray spectroscopy, and photoluminescence spectroscopy are all used to characterize the as-prepared samples. Experiments peformed with different reaction times indicate that a central-etching of the plates from the inner part towards the edge during nanocrystal growth plays a key role in the formation of LaF3 nanorings since no other templates/surfactants are present in our system. Additionally, the luminescence properties of LaF3 nanorings doped with Eu3+ cation have been investigated andcompared with those of bulk materials and nanoparticles with a size of approximately 50 nm. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] InN@SiO2 Nanomaterials as New Blue Light EmittersEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2008Prabhakaran Munusamy Abstract In this article we report blue photoluminescence (, 450 nm) from InN@SiO2 nanomaterials. The InN@SiO2 nanomaterials were prepared by a simple precipitation reaction followed by a solid-state reaction. Various control experiments demonstrate that the interface between the InN and SiO2 seems to play a crucial role in the origin of the blue emission from the InN@SiO2 nanomaterial. The InN@SiO2 nanomaterial was characterized by using analytical methods such as TEM, XRD, Raman, XPS, and photoluminescence spectroscopy, which confirmed the existence of InN on SiO2 with a small excess of nitrogen relative to indium.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Synthesis and Luminescent Properties of Novel Europium(III) Heterocyclic ,-Diketone Complexes with Lewis Bases: Structural Analysis Using the Sparkle/AM1 ModelEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2005Rani Pavithran Abstract Tris(,-diketonato)europium(III) complexes of general formula [Eu(TPI)3·L], with chelating ligands such as 3-phenyl-4-(4-toluoyl)-5-isoxazolone (HTPI) and adduct-forming reagents [L = H2O, tri- n -octylphosphane oxide (TOPO), triphenylphosphane oxide (TPhPO), 1,10-phenanthroline], have been synthesized and characterized by elemental analysis and FT-IR, 1H NMR, and photoluminescence spectroscopy. The coordination geometries of the complexes were calculated using the Sparkle/AM1 (Sparkle model for the calculation of lanthanide complexes within the Austin model 1) model. The ligand,Eu3+ energy-transfer rates were calculated using a model of intramolecular energy transfer in lanthanide coordination complexes reported in the literature. The room-temperature PL spectra of the europium(III) complexes are composed of the typical Eu3+ red emission, assigned to transitions between the first excited state (5D0) and the multiplet (7F0,4). The results clearly show that the substitution of water molecules by TOPO leads to greatly enhanced quantum yields (i.e., 1.3,% vs. 49.5,%) and longer 5D0 lifetimes (220 vs. 980 ,s). This can be ascribed to a more efficient ligand-to-metal energy transfer and a less efficient nonradiative 5D0 relaxation process. The theoretical quantum yields are in good agreement with the experimental quantum yields, which highlights that the present theoretical approach can be a powerful tool for the a priori design of highly luminescent lanthanide complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Quantum-Dot-Functionalized Poly(styrene- co -acrylic acid) Microbeads: Step-Wise Self-Assembly, Characterization, and Applications for Sub-femtomolar Electrochemical Detection of DNA HybridizationADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Haifeng Dong Abstract A novel nanoparticle label capable of amplifying the electrochemical signal of DNA hybridization is fabricated by functionalizing poly(styrene- co -acrylic acid) microbeads with CdTe quantum dots. CdTe-tagged polybeads are prepared by a layer-by-layer self-assembly of the CdTe quantum dots (diameter,=,3.07,nm) and polyelectrolyte on the polybeads (diameter,=,323,nm). The self-assembly procedure is characterized using scanning and transmission electron microscopy, and X-ray photoelectron, infrared and photoluminescence spectroscopy. The mean quantum-dot coverage is (9.54,±,1.2),×,103 per polybead. The enormous coverage and the unique properties of the quantum dots make the polybeads an effective candidate as a functionalized amplification platform for labelling of DNA or protein. Herein, as an example, the CdTe-tagged polybeads are attached to DNA probes specific to breast cancer by streptavidin,biotin binding to construct a DNA biosensor. The detection of the DNA hybridization process is achieved by the square-wave voltammetry of Cd2+ after the dissolution of the CdTe tags with HNO3. The efficient carrier-bead amplification platform, coupled with the highly sensitive stripping voltammetric measurement, gives rise to a detection limit of 0.52 fmol L,1 and a dynamic range spanning 5 orders of magnitude. This proposed nanoparticle label is promising, exhibits an efficient amplification performance, and opens new opportunities for ultrasensitive detection of other biorecognition events. [source] Charge Transfer Excitons in Polymer/Fullerene Blends: The Role of Morphology and Polymer Chain ConformationADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Markus Hallermann Abstract Here, it is shown how carrier recombination through charge transfer excitons between conjugated polymers and fullerene molecules is mainly controlled by the intrachain conformation of the polymer, and to a limited extent by the mesoscopic morphology of the blend. This experimental result is obtained by combining near-infrared photoluminescence spectroscopy and transmission electron microscopy, which are sensitive to charge transfer exciton emission and morphology, respectively. The photoluminescence intensity of the charge transfer exciton is correlated to the degree of intrachain order of the polymer, highlighting an important aspect for understanding and limiting carrier recombination in organic photovoltaics. [source] One-Dimensional Microwires Formed by the Co-Assembly of Complementary Aromatic Donors and AcceptorsADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Jie-Yu Wang Abstract A truxene derivative (Tr3) with a C3 symmetric conjugated plane is synthesized; this derivative is a perfect match, in both size and structure, with its oxidized counterpart, the truxenone derivative (TrO3), a new electron acceptor that was recently reported. The complementary pair, Tr3 and TrO3, sets a good platform for the investigation of aromatic donor,acceptor interactions. Detailed 1H NMR experiments, photoluminescence spectroscopy, as well as differential scanning calorimetry are performed to investigate the interaction between Tr3 and TrO3, from solution to mesophase. One-dimensional microbelts readily formed from a 1:1 mixture of Tr3 and TrO3. Scanning electron microscopy, powder X-ray diffraction, as well as fluorescence microscopy are performed to elucidate their co-assembly structure in the solid state. Moreover, modulation of the co-assembly structure is easily realized by changing the concentration or mixing ratio. The present system opens the possibility of forming 1D heterostructures via electron donor,acceptor interaction, and its potential application as P,N junction and photowaveguide materials in optoelectronic devices. [source] ZnSe,Si Bi-coaxial Nanowire Heterostructures,ADVANCED FUNCTIONAL MATERIALS, Issue 9 2005R. Wang Abstract We report on the fabrication, structural characterization, and luminescence properties of ZnSe/Si bi-coaxial nanowire heterostructures. Uniform ZnSe/Si bi-coaxial nanowire heterostructures are grown on silicon substrates by the simple one-step thermal evaporation of ZnSe powder in the presence of hydrogen. Both ZnSe and silicon are single-crystalline in the bi-coaxial nanowire heterostructures, and there is a sharp interface along the nanowire axial direction. Furthermore, secondary nanostructures of either ZnSe nanobrushes or a SiOx sheath are also grown on the primary bi-coaxial nanowires, depending on the ratio of the source materials. The experimental evidence strongly suggests that bi-coaxial nanowires are formed via a co-growth mechanism, that is, ZnSe terminates specific surfaces of silicon and leads to anisotropic, one-dimensional silicon growth, which simultaneously serves as preferential nucleation sites for ZnSe, resulting in the bi-coaxial nanowire heterostructures. In addition, the optical properties of ZnSe/Si nanowires are investigated using low-temperature photoluminescence spectroscopy. [source] Continuous Flow Supercritical Chemical Fluid Deposition of Optoelectronic Quality CdSADVANCED MATERIALS, Issue 41 2009Jixin Yang Supercritical chemical fluid deposition (SCFD) has been shown to have remarkable advantages for deposition inside nanostructured templates however so far the technique has mostly been used to deposit metals. In this paper we present the SCFD of optoelectronic grade CdS. The quality of this material is demonstrated by a range of techniques including reflectivity (A) and photoluminescence spectroscopy (B and C). At 4,K the bandedge luminescence has a full-width-at-half-maximum linewidth of 30,meV comparable with that of single crystal CdS. [source] Fabrication of Vertically Well-Aligned (Zn,Mn)O Nanorods with Room Temperature Ferromagnetism,ADVANCED MATERIALS, Issue 22 2005M. Baik Vertically well-aligned (Zn,Mn)O nanorods (see Figure) that show ferromagnetic behavior at room temperature have been grown on sapphire substrates by chemical vapor deposition. The high optical quality of the nanorods has been demonstrated by photoluminescence spectroscopy. These nanowires may find use in future nanoscale magneto-optic and magneto-electronic applications. [source] Photoluminescence of Self-organized Perylene Bisimide PolymersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2004Edda E. Neuteboom Abstract Summary: Three polymers consisting of alternating perylene bisimide chromophores and flexible polytetrahydrofuran segments of different length have been studied using absorption and (time-resolved) photoluminescence spectroscopy. In o -dichlorobenzene, the chromophores self organize to form H-like aggregates. The photoluminescence spectra of the self-organized polymers consist of vibronically resolved monomeric perylene bisimde fluorescence (,max,=,538 nm, ,,=,3.9 ns) and unstructured excimer-type emission (,max,=,635 nm, ,,=,17 ns). An additional short-lived (,,,,2 ns) luminescence component is observed and ascribed to the dynamic deactivation of the monomeric photoexcited state via excimer formation or energy transfer. Structure of alternating perylene bisimide , polyTHF copolymers. [source] Structure and Properties of CdS/Regenerated Cellulose NanocompositesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2005Dong Ruan Abstract Summary: Novel inorganic-organic hybrid materials composed of cadmium sulfide (CdS) semiconducting nanocrystals and regenerated cellulose (RC) were prepared by using in situ synthesizing method. Cellulose was dissolved in a 6 wt.-% NaOH/4 wt.-% urea/thiourea aqueous solution at low temperature followed by addition of cadmium chloride (CdCl2), resulting that the CdS nanocrystals were successfully grown in situ in the cellulose solution. Nanocomposite films containing homogeneous CdS nanoparticles were obtained by casting the resulting solution. Their structure and optical properties were characterized by X-ray photoelectron spectroscopy, wide-angle X-ray diffraction, thermogravimetry analysis, dynamic mechanical analysis, atomic force microscopy, transmittance electronic microscope, UV-vis spectroscopy, and photoluminescence spectroscopy. The experimental results confirmed that the CdS nanocrystalline existed in the composite films, and cellulose matrix provided a confined medium for CdS particle growth in uniform size. The CdS/RC composites showed narrow emission in photoluminescence spectra, and their optical absorbance in the UV range was higher than that of the cellulose film without CdS. This work provided a simple method to prepare cellulose functional materials in NaOH/urea aqueous solution. Photoluminescence of CdS/RC nanocomposites and TEM image of CdS nanocrystals dispersed in RC matrix. [source] Fabrication and characteristics of SiOx -core nanowires: Comparison study between uncoated and ZnO-coated SiOx nanowiresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2008Hyoun Woo Kim Abstract We have demonstrated an approach to the synthesis of SiOx -core nanowires, on which ZnO shell layer would be subsequently deposited. We have discussed the possible growth mechanism of SiOx nanowires, in regard to the role of Au catalyst. For a comparison study between uncoated and coated nanowires, samples were characterized by X-ray dif- fraction (XRD), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). This method can be applied to a wide range of materials and results in various heterostructures, which may serve as potential building blocks in various nanodevices. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of growth temperature on exciton lifetime and structural properties of ZnO films on sapphire substratePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2006S. Cho Abstract We report on optimization of growth conditions by studying the structural and optical properties of ZnO films grown on sapphire substrate by pulsed laser deposition at different growth temperatures. The crystallographic structure and surface morphology were studied by X-ray diffraction and atomic force microscopy, respectively. The flattest surface was observed in the sample grown at substrate temperature of 500 °C. The optical characterization was performed by steady state and time resolved photoluminescence spectroscopy. Photoluminescence of the samples was studied at low CW excitation and at high-power-density pulsed excitation in picosecond domain. Stimulated emission was observed at pulsed excitation. Carrier lifetimes were found to significantly depend on the growth temperature reaching the peak value also in the samples grown at approximately 500 °C. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] How to avoid non-radiative escape of excitons from quantum dots?PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2004I. C. Robin Abstract We investigated the transition between two different exciton recombination regime in quantum dots depending on temperature. When temperature is raised above a threshold value that we determine experimentally non-radiative recombination channels, characterized by their activation energy, dominate over radiative recombination. The analyses of time resolved photoluminescence spectroscopy versus temperature shows that the maximum temperature for dominant radiative recombination scales linearly with the activation energy of the non-radiative channels over a large range of values (10,60 meV) measured for various kind of II,VI-based quantum dots: CdTe/ZnTe, CdTe/ZnMgTe, CdSe/ZnSe. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] EPR and photoluminescence diagnostics of singlet oxygen generation on porous silicon surfacePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2009E. A. Konstantinova Abstract Electron paramagnetic resonance and photoluminescence spectroscopy are used to investigate photosensitized generation of singlet oxygen in the porous silicon layers. The singlet oxygen concentration in the samples was estimated at various oxygen pressures. The time of energy transfer from excitons confined in Si nanocrystals to adsorbed O2 molecules on silicon nanocrystal surface and photosensitization efficiency are found to depend on the porosity of the samples. The singlet oxygen generation efficiency increases strongly for porous silicon with high (>80%) porosity. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Time-resolved spectroscopy in an undoped GaN (1-101)PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008Eunhee Kim Abstract Time-resolved photoluminescence spectroscopy was performed at 77 K in a GaN (1-101) grown on a 7 degree off-axis (001) Si substrate. The sample was grown by metal-organic-vapour-phase-epitaxy (MOVPE) and was un-intentionally doped with O, C and Si. By using photoluminescence intensity correlation method, the energy relaxation process of the photogenerated carriers near the band edge was investigated in pico-second regime. The correlation signal was represented by a single exponential decay curve and the energy relaxation time was determined, which depended strongly on the kinetic energy of the excess carriers. At low energies, the relaxation time was around 700 ps, while it was as short as a few ps at the highest energy under study. The correlation signals obtained for carriers of which kinetic energy was less than 80 meV showed an anti-correlation behaviour suggesting the occurrence of carrier accumulation. The time constants for the accumulation were of several picoseconds depending on the kinetic energy, which was nearly equal to the decay time constants determined at high energies. This fact shows that the energy relaxation at high energies is controlled by the emission of an LO phonon. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ce and Yb doped InP layers grown for radiation detectionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2007J. Zavadil Abstract InP single crystals were grown by liquid phase epitaxy on semi-insulating InP:Fe substrate with cerium (Ce) and ytterbium (Yb) additions to the growth melt. Grown layers were characterised by Hall measurements and low temperature photoluminescence spectroscopy. Both types of layers exhibit the change of electrical conductivity from n to p type. Ce and Yb have been found to be incorporated into the InP lattice since a sharp luminescence lines arising from inner shell transitions of Yb3+ and Ce3+ were detected at 1002 and 3534 nm, respectively. A metastable conductivity state of InP:Ce layers has been found at temperatures below 35 K, a phenomenon previously reported for InP:Yb layers. Similar electrical behaviour of InP (Ce, Yb) layers leads us to conclude that Ce acts as dominant acceptor impurity responsible for n,p conductivity change. (© 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] The exciton polariton model and the diffusion of excitons in ZnO analyzed by time-dependent photoluminescence spectroscopyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006R. Hauschild Abstract We investigate the lineshape of the zero-phonon luminescence of the A-exciton polariton and of the LO-phonon replicas in ZnO and their dynamics. The lineshape verifies details of the A-exciton polariton model and confirms the inverted band structure (A,7, B,9, C,7). The dynamics give information on relaxation, diffusion and recombination processes. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spectral characteristics of single InAs/InGaAs quantum dots in a quantum wellPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003L. Worschech Abstract Self assembled InAs quantum dots embedded in an InGaAs quantum well were grown by molecular beam epitaxy. At room temperature these dots in a well (DWELLS) have an emission wavelength of 1.3,,m. Small mesas with lateral sizes down to 200 × 200 nm2 were fabricated by electron beam lithography and etching techniques. By photoluminescence spectroscopy at low temperatures we observe narrow lines, which we attribute to excitons and excitonic molecules. Biexciton binding energies ranging between 3.5,5,meV are found. [source] Degradation of Structural and Optical Properties of InGaN/GaN Multiple Quantum Wells with Increasing Number of WellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003S. Pereira Abstract We compare the structural and spectral properties of two multi quantum wells (MQWs), grown by metal organic chemical vapour deposition under the same nominal conditions, with a different number of periods. The MQWs, each with 20% InN and containing 8 and 18 wells, respectively, grew on-axis and coherent to GaN, as revealed by X-ray diffraction reciprocal space mapping (RSM) analysis. Comparison of the asymmetrical (105) RSMs indicates an overall structural deterioration and greater well-barrier intermixing for the MQW with the larger number of wells. Moreover, the composition of the MQWs was depth-profiled by grazing incidence Rutherford backscattering spectrometry (RBS). RBS further evidences strong intermixing in the 18-well heterostructure. The deleterious effects of intermixing on the emission spectrum are revealed by low temperature photoluminescence spectroscopy. Despite similar peak emission energies (,E < 45 meV) the 8-well structure shows a more symmetric and narrow peak (FWHM , 100 meV) in comparison with that of the 18-well sample (FWHM , 170 meV). Surface analyses by atomic force and scanning electron microscopy show an increased density, size and depth of V-pit defects on the 18-well structure. These results suggest that dislocations and pitting result from a larger elastic strain energy accumulated in the thicker MQW stack and are a fundamental intermixing mechanism for InGaN/GaN MQWs. [source] | ||||||||||||||||