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Photoluminescence Intensity (photoluminescence + intensity)
Selected AbstractsAnti-Stokes photoluminescence in CdSe self-assembled quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003Aishi Yamamoto Abstract Anti-Stokes photoluminescence (ASPL) as well as Stokes photoluminescence (SPL) were studied in CdSe self-assembled quantum dots using a micro-photoluminescence technique. A few ASPL peaks were observed, and they also appeared in the SPL spectra. Photoluminescence intensities of both ASPL and SPL increase linearly with the excitation intensity. The emission mechanism of the observed ASPL is discussed. [source] Influence of Mg on the temperature-dependent optical properties of CdTe quantum dots embedded in Zn0.7Mg0.3TePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004Frank Tinjod Abstract We compare the temperature-dependent optical properties of CdTe quantum dots with and without Mg in their Zn(Mg)Te barriers. The difficulty of forming CdTe dots on Zn0.7Mg0.3Te barriers (due to the decrease of the lattice mismatch) has been overcome by using a new technique based on an efficient reduction of the surface energy. Mg incorporation in the barriers leads to a better heavy-hole confinement along the growth axis, which is manifested in PL studies by both an extension of the radiative regime temperature range and a strong increase of the activation energy for the non-radiative mechanisms. However, the in-plane confinement is less enhanced, which leads to progressive inter-dot carrier transfers with increasing temperature, as evidenced directly by the analysis of photoluminescence intensities for different single dots. Our temperature-dependent data (time-resolved and micro-photoluminescence) indicate that this transfer consists of a thermally activated process via the two-dimensional wetting-layer states. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis of Magnetic, Up-Conversion Luminescent, and Mesoporous Core,Shell-Structured Nanocomposites as Drug CarriersADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Shili Gai Abstract The synthesis (by a facile two-step sol,gel process), characterization, and application in controlled drug release is reported for monodisperse core,shell-structured Fe3O4@nSiO2@mSiO2@NaYF4: Yb3+, Er3+/Tm3+ nanocomposites with mesoporous, up-conversion luminescent, and magnetic properties. The nanocomposites show typical ordered mesoporous characteristics and a monodisperse spherical morphology with narrow size distribution (around 80,nm). In addition, they exhibit high magnetization (38.0,emu g,1, thus it is possible for drug targeting under a foreign magnetic field) and unique up-conversion emission (green for Yb3+/Er3+ and blue for Yb3+/Tm3+) under 980,nm laser excitation even after loading with drug molecules. Drug release tests suggest that the multifunctional nanocomposites have a controlled drug release property. Interestingly, the up-conversion emission intensity of the multifunctional carrier increases with the released amount of model drug, thus allowing the release process to be monitored and tracked by the change of photoluminescence intensity. This composite can act as a multifunctional drug carrier system, which can realize the targeting and monitoring of drugs simultaneously. [source] Functionalized Self-Assembled InAs/GaAs Quantum-Dot Structures Hybridized with Organic MoleculesADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Miaoxiang Chen Abstract Low-dimensional III,V semiconductors have many advantages over other semiconductors; however, they are not particularly stable under physiological conditions. Hybridizing biocompatible organic molecules with advanced optical and electronic semiconductor devices based on quantum dots (QDs) and quantum wires could provide an efficient solution to realize stress-free and nontoxic interfaces to attach larger functional biomolecules. Monitoring the modifications of the optical properties of the hybrid molecule,QD systems by grafting various types of air-stable diazonium salts onto the QD structures surfaces provides a direct approach to prove the above concepts. The InAs/GaAs QD structures used in this work consist of a layer of surface InAs QDs and a layer of buried InAs QDs embedded in a wider-bandgap GaAs matrix. An enhancement in photoluminescence intensity by a factor of 3.3 from the buried QDs is achieved owing to the efficient elimination of the dangling bonds on the surface of the structures and to the decrease in non-radiative recombination caused by their surface states. Furthermore, a narrow photoluminescence band peaking at 1620,nm with a linewidth of 49 meV corresponding to the eigenstates interband transition of the surface InAs QDs is for the first time clearly observed at room temperature, which is something that has rarely been achieved without the use of such engineered surfaces. The experimental results demonstrate that the hybrid molecule,QD systems possess a high stability, and both the surface and buried QDs are very sensitive to changes in their surficial conditions, indicating that they are excellent candidates as basic sensing elements for novel biosensor applications. [source] Combined Optical and MR Bioimaging Using Rare Earth Ion Doped NaYF4 NanocrystalsADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Rajiv Kumar Abstract Here, novel nanoprobes for combined optical and magnetic resonance (MR) bioimaging are reported. Fluoride (NaYF4) nanocrystals (20,30,nm size) co-doped with the rare earth ions Gd3+ and Er3+/Yb3+/Eu3+ are synthesized and dispersed in water. An efficient up- and downconverted photoluminescence from the rare-earth ions (Er3+ and Yb3+ or Eu3+) doped into fluoride nanomatrix allows optical imaging modality for the nanoprobes. Upconversion nanophosphors (UCNPs) show nearly quadratic dependence of the photoluminescence intensity on the excitation light power, confirming a two-photon induced process and allowing two-photon imaging with UCNPs with low power continuous wave laser diodes due to the sequential nature of the two-photon process. Furthermore, both UCNPs and downconversion nanophosphors (DCNPs) are modified with biorecognition biomolecules such as anti-claudin-4 and anti-mesothelin, and show in vitro targeted delivery to cancer cells using confocal microscopy. The possibility of using nanoprobes for optical imaging in vivo is also demonstrated. It is also shown that Gd3+ co-doped within the nanophosphors imparts strong T1 (Spin-lattice relaxation time) and T2 (spin-spin relaxation time) for high contrast MR imaging. Thus, nanoprobes based on fluoride nanophosphors doped with rare earth ions are shown to provide the dual modality of optical and magnetic resonance imaging. [source] Variety of photoluminescence intensity of fluorescent whitening agents introduced into polyacrylonitrile nanofibersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Shugang Wang Abstract The major objective in this study was the preparation of polyacrylonitrile (PAN) nanofibers composed of 1,4-bis(o -cyanostyryl)benzene (ER) and 1-(o -cyanostyryl)-4-(p -cyanostyryl)benzene (EB), two kinds of fluorescent whitening agents widely used in the textile industry. The scanning electron microscopy images revealed that the diameters of ER/PAN and EB/PAN fibers ranged from 78 to 154 nm. The IR spectra indicated that the peaks of the CN group blueshift and the generation of a shoulder peak were obviously due to the interaction between ER or EB and PAN. Furthermore, the UV spectra demonstrated that the distributive status of ER or EB tended toward the molecular state in PAN nanofibers. Finally, the most interesting finding in this study was that the photoluminescence intensity of EB/PAN nanofibers increased magnificently, whereas that of ER/PAN nanofibers decreased remarkably. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2382,2386, 2007 [source] Atomic structure of pyramidal defects in GaN:Mg: Influence of annealingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006Z. Liliental-Weber Abstract The atomic structure of the characteristic defects (Mg-rich hexagonal pyramids) in p-doped bulk and MOCVD GaN:Mg thin films grown with Ga polarity was determined at atomic resolution by direct reconstruction of the scattered electron wave in a transmission electron microscope. Small cavities were present inside the defects, confirmed also with positron annihilation. The inside walls of the cavities were covered by GaN of reverse polarity compared to the matrix. Annealing of the MOCVD layers lead to slight increase of the defect size and an increase of the room temperature photoluminescence intensity. Positron annihilation confirms presence of vacancy clusters of different sizes triggered by the Mg doping in as-grown samples and decrease of their concentration upon annealing at 900 and 1000 °C. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] resonance enhancement of photoluminescence from silicon nanocrystallitesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2009L. V. Belyakov Abstract An interaction of molecular oxygen and p-Si nanocrystallites in HF,ethanolic solution with simultaneous illumination has been investigated. It is shown that after such treatment with white-light exposure the photoluminescence from nanocrystallites enhances substantially caused by photogenerated singlet forms of molecular oxygen. In the case of monochromatic illumination with photon energy in the range 2.5,0.95 eV dependence of photoluminescence intensity after the treatment on photon energy used shows resonant peaks corresponding to the absorbance peaks of excited molecular oxygen. To our knowledge such photoluminescence peaks in porous silicon spectroscopy have been observed for the first time. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Zero dimensional exciton-polaritonsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2006A. Baas The cover picture from the article [1] shows, in the left parts of the three diagrams, the measured photoluminescence intensity as a function of energy and emission angle for a 3 ,m (left diagram), 9 ,m (middle diagram) and 19 ,m-diameter quasi-circular mesa (right diagram). The white lines are the energy dispersions of 2D polariton modes. For clarity, intensities above 1485 meV have been multiplied by a constant factor, as indicated. The right parts of the diagrams contain intensity plots of the simulated polariton spectral density for cylindrical mesas of the same diameters, yielding very good quantitative agreement of the 0D polariton states in the circular mesas. This confirms the coexistence of 0D and 2D microcavity polaritons in these semiconductor structures. This paper is an invited presentation from the 8th International Workshop on Nonlinear Optics and Excitation Kinetics. Further articles from NOEKS 8 are published in phys. stat. sol. (c) 3, No. 7 (2006). [source] Improvement of photoluminescence efficiency in stacked Ge/Si/Ge quantum dots with a thin Si spacerPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2004P. S. Chen Abstract In this work, two successive layers of Ge quantum dots separated by a thin Si spacer grown by ultra-high-vacuum chemical vapor deposition were demonstrated. With an optimal thickness of the thin Si spacer, the sandwiched Ge (13.1 ML)/Si (28 ML)/Ge (13.1 ML) quantum dots suppress the coarsening of Ge quantum dots and efficiently increase the uniformity of the quantum dots. Cross-sectional transmission electron microscopy shows that the Si/Ge underlayers provide preferred nucleation sites for the overlayer Ge deposition. Such a modification avoids the formation of Ge superdomes and prevents the occurrence of threading dislocations even at such a thin Si spacer thickness. A stronger photoluminescence intensity of these sandwich Ge/Si/Ge quantum dots was observed compared with that of 26.2 eq-ML Ge quantum dots without using any intermediate Si layer. Furthermore, the narrower width of the photoluminescence spectra indicates that the Ge/Si/Ge dots are more uniform compared with the 13.1 and 26.1 eq-ML Ge quantum dots. Five-fold bilayers of Ge/Si/Ge/Si(150 ML) have been achieved to enhance the photo-emission efficiency. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Linear polarized photoluminescence from GaN quantum dots imbedded in AlN matrixPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010K. S. Zhuravlev Abstract We report microphotoluminescence studies of GaN/AlN quantum dots grown along the (0001) crystal axis by molecular-beam epitaxy on sapphire substrates. To obtain quantum dots with different density and size a nominal GaN coverage was varied from 1 to 4 monolayers. The highest density of quantum dots was about 1011 cm -2, so about 103 quantum dots was excited in experiments. We found that the photoluminescence intensity of a sample with the smallest amount of deposited GaN decreases in more than two orders of magnitude under continuous-wave laser exposure during about 30 minutes and then it remains stable. The photoluminescence intensity of the rest samples was time-independent quantity. The emission band of the former sample exhibits a prominent linear polarization along the growth plane. We assume that the quite high degree of polarization can be due anisotropy of strain and/or shape of the quantum dots formed near dislocations which act also as recombination centers causing photoluminescence quenching. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Luminescence and vibrational properties of erbium-implanted nanoporous GaNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008C. B. Soh Abstract Implantation of erbium (Er) into GaN is useful in creating selected areas to emit at the green, yellow and infrared wavelengths. Enhanced erbium activation is obtained when erbium is implanted into porous GaN formed by electrochemical etching than into as-grown GaN. This is due to the increase in surface areas for light extraction and the availability of more free surfaces to accommodate strain when it is annealed. Furnace annealing at 1100 °C for 30 mins in nitrogen gives rise to higher band-edge photoluminescence intensity. Apart from the host GaN phonon modes, we have also observed disorder-induced lattice vibrations at 170, 200 and 350-365 cm,1 from Er-implanted porous GaN. The E2 (high) mode of GaN also shifts towards higher energy at higher annealing temperatures, indicative of more erbium occupying the VGa site (ionic radii of Er > Ga) and hence increasing the compressive stress in the GaN crystal lattice. The prominent defect-induced local vibrational modes in Er-doped nanoporous GaN are also observed in ultraviolet resonant Raman scattering. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Single photon correlation measurements in a study of excitation process of individual CdTe/ZnTe quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2006J. Suffczy Abstract We present the results of systematic autocorrelation and cross-correlation measurements performed on photons originating from various excitonic transitions in a single CdTe/ZnTe quantum dot (QD). Excitation power dependence of photoluminescence intensity was also measured on the same dot under the same experimental conditions. Recorded correlation histograms have provided evidence for memory effects in QD photoluminescence extending over a few excitation periods. Rate equation model assuming a ladder of states and excitation through a single carrier and exciton capture, is fitted to the data. As a consequence, simultaneous quantitative description of the results of both, correlation and power dependence, is obtained. Strong evidence is presented for a QD excitation by capture of single carriers rather than entire excitons. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thin film electroluminescent cells on the basis of Ce-doped CaGa2S4 and SrGa2S4 prepared by flash evaporation methodPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006E. Gambarov Abstract Ce-doped CaGa2S4 and SrGa2S4 thin film electroluminescent (TFEL) devices were prepared for the first time on the basis of films deposited by flash evaporation method. Significant crystallization, stoichiometry improvement of the films and increase of photoluminescence intensity were found after annealing in H2S and O2 gas stream. EL spectra of the cells exhibited the characteristic double-band emission similar to that seen for Ce3+ activated CaGa2S4 and SrGa2S4 films under photon excitation. Applied voltage and frequency dependences of the electroluminescence were studied. Low voltage operation as low as 20 V was observed for these cells. Luminance of about 4 cd/m2 at 100 V operating voltage with 2.5 kHz frequency was achieved for the TFEL cell with films annealed in O2 gas stream. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||