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Luminescence Spectra (luminescence + spectrum)
Selected AbstractsGrowth and characterization of Nd, Yb , yttrium oxide nanopowders obtained by sol-gel methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2007A. Rzepka Abstract Nanopowders of Y2O3 pure, doped and codoped by Nd3+, Yb3+ were obtained by sol-gel method. Solution with ethylene glycol was choosed as the proper solution where crystallites of powder with Nd and Yb dopants had the same size. Finally the one-phased compounds of Y2O3 doped 0.5 at% Nd and 1, 2 or 4 at% Yb were obtained. Grain growth and their morphology were investigated in various temperature and time of heating. The changes of crystallite sizes and lattice constants in relation to the heating time and temperature for the composition Y2O3 doped 0.5 at% Nd and 2 at% Yb are presented. Y2O3 containing 0,5 at% of Nd exhibits intense luminescence bands centered at 920 nm, 1100 nm and 1360 nm whereas a single band at about 1020 nm appears in samples co-doped with neodymium and ytterbium. Luminescence spectra recorded did not depend on the sample preparation procedure and size of grains. OH impurity affects critically the relaxation dynamics of luminescent ion in nanopowders. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Preparation, characterization, and electrical properties of dual-emissive Langmuir-Blodgett films of some europium-substituted polyoxometalates and a platinum polyyne polymerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2010Li Liu Abstract A new series of organometallic/inorganic composite Langmuir-Blodgett (LB) films consisting of a rigid-rod polyplatinyne polymer coordinated with 2,7-bis(buta-1,3-diynyl)-9,9-dihexylfluorene (denoted as PtP) as the ,-conjugated organometallic molecule, an europium-substituted polyoxometalate (POM; POM = Na9EuW10O36, K13[Eu(SiW11O39)2] and K5[Eu(SiW11O39)(H2O)2]) as the inorganic component, and an amphiphilic behenic acid (BA) as the auxiliary film-forming agent were prepared. Structural and photophysical characterization of these LB films were achieved by ,,A isotherms, absorption and photoluminescence spectra, atomic force microscopy imaging, scanning tunneling microscopy, and low-angle X-ray diffraction. Our experimental results indicate that stable, well-defined, and well-organized Langmuir and LB films are formed in pure water and POM subphases, and the presence of Eu-based POM in the subphase causes an area expansion. It is proposed that a lamellar layered structure exists for the PtP/BA/POM LB film in which the POM and PtP molecules can lay down with the interfacial planes. Luminescence spectra of the prepared hybrid LB films show that near-white emission spectra can be obtained due to the dual-emissive nature of the mixed PtP/POM blends. These Pt-polyyne-based LB films displayed interesting electric conductivity behavior. Among them, PtP/BA/POM 13-layer films showed a good electrical response, with the tunneling current up to ±100 nA when the voltage was monitored between ,1 and 7 V. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 879,888, 2010 [source] Origin of red luminescence of sodium titanium phosphate crystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005R.S. Boyko Abstract Sodium titanium orthophosphate NaTi2(PO4)3 crystals were synthesized and their luminescence properties were investigated. Luminescence spectra of this compound consist of two main bands in the green and red spectral regions. Maximum positions of the bands depend on temperature of the samples. At some conditions the red band reveals details of a fine spectra structure. Obtained results are discussed taking into account similarity of spectral properties of the investigated crystals with ones described recently for sodium aluminum diphosphate crystals doped with chromium ions. Conclusion is made that red emission band is corresponded to radiation transitions in the Ti3+ titanium ions. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Luminescence spectra in metallic and ferromagnetic GaMnAs/GaAs multilayers: a self-consistent super-cell Kane k.p calculationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2004G. M. Sipahi Abstract We present a self-consistent Kane k.p calculation for obtaining the luminescence spectra of GaMnAs/GaAs multilayers. Our model consists of substitutional Mn ions uniformly distributed in GaMnAs layers of width d1 at a concentration of 5%. The high Mn concentration allows to approximating the density of the magnetic moments by a continuous distribution when treating the magnetic interaction between holes and the localized moment on the Mn++ sites. These DMS layers are assumed to be ferromagnetic, at T = 0 K, metallic, and with a hole concentration equivalent, in bulk, to 1 × 1020 cm,3. The DMS layers are separated by non-magnetic GaAs layers. The magnetization is kept perpendicular-to-the-plane (parallel to the growth direction) by the application of a weak magnetic field, which does not affect the electronic structure directly. The luminescence spectrum is obtained for several numbers of DMS layers in the structure. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Theory of laser cooling of semiconductor quantum wellsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2008G. Rupper Abstract We present a microscopic many-body theory of laser cooling of semiconductor quantum wells. The cooling mechanism is the upconversion of pump photons through absorption and subsequent luminescence by an electron,hole,exciton mixture maintained at steady state in the quantum well. Assuming this Coulomb plasma to be in quasi-thermal equilibrium, our theory calculates its absorption/luminescence spectra within a diagrammatic (real-time) Green's function approach at the self-consistent T-matrix level. These spectra are used in a cooling threshold analysis for GaAs quantum wells that also takes into account other losses into heat. We compare the present results with previous ones obtained for bulk GaAs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Theory of semiconductor laser cooling at low temperaturesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2006G. Rupper Abstract We present a microscopic many-body theory of laser cooling of semiconductors. Using a standard diagrammatic Green's function approach, we calculate the absorption/luminescence spectra of a partially ionized electron-hole plasma in quasi-equilibrium at the self-consistent T-matrix level. This theory is applied to studying criteria of cooling threshold and efficiency in bulk GaAs, focusing mainly on the temperature range between 5 K and 100 K. In particular, we discuss the transition from the high temperature regime dominated by absorption in the e-h continuum to the low temperature regime dominated by resonant exciton absorption. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Variability in the Structures of Luminescent [2-(Aminomethyl)pyridine]silver(I) Complexes: Effect of Ligand Ratio, Anion, Hydrogen Bonding, and ,-StackingEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2005Rodney P. Feazell Abstract The reaction of 2-(aminomethyl)pyridine (2-amp) with silver(I) salts of triflate (OTf,), trifluoroacetate (tfa,), and tetrafluoroborate (BF4,) produce monomeric, dimeric, bridged, and polymeric structural motifs. The structural characteristics are dependent upon the ratio of ligand/metal in the structure as well as the ability of the anion to coordinate to the metal centers and form hydrogen bonds to the bound ligands. The silver coordination environment takes on several geometries including near linear (6), trigonal (4), tetrahedral (1), and both trigonal-bipyramidal and square-based pyramidal in a single structure (2). Structures 2, 3, and 5 also display short Ag,Ag contacts ranging from 2.8958(3) to 3.0305(4) Å. The species with metal,metal interactions, which are connectively very similar to their metal-isolated counterparts of 1, 4, and 6, are held together only by weak ,-stacking interactions or hydrogen bonds to their respective anions. Low-temperature luminescence spectra were collected for all compounds and are compared. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Synthesis of meso -Coumarin-Conjugated Porphyrins and Investigation of Their Luminescence PropertiesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 26 2007Weiying Lin Abstract A series of meso -coumarin-conjugated porphyrins 1a,e were designed and synthesized. Condensation of 4-chloroacetoacetate ethyl ester with m -cresol or resorcin afforded 4-chloromethylcoumarins, which were then hydrolyzed to give coumarin alcohols, followed by oxidation to provide coumarin aldehydes. The reaction of coumarin aldehydes with pyrrole under Adler or Lindsey conditions afforded the meso -coumarin-conjugated porphyrins 1a,e. Their UV/Vis absorption spectra and photoluminescent spectra were recorded both in dilute THF solution and as solid films. Analysis of the luminescence spectra indicate that the energy transfer from the coumarin substituents to the porphyrin core for 1a,e is more efficient in solid film than in solution, and the energy transfer from the coumarin substituent to the porphyrin core for 1d and 1e is more efficient than that of 1a, 1b and 1c in solid film. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Effects of Zinc(II) on the Luminescence of Europium(III) in Complexes Containing , -Diketone and Schiff BasesHELVETICA CHIMICA ACTA, Issue 11 2009Yuko Hasegawa Abstract The UV, excitation, and luminescence spectra of tris(pivaloyltrifluoroacetonato)europium(III) ([Eu(pta)3]; Hpta=1,1,1-trifluoro-5,5-dimethylhexane-2,4-dione=HA) were measured in the presence of bis(salicylidene)trimethylenediamine (H2saltn), bis[5-(tert- butyl)salicylidene]trimethylenediamine (H2(tBu)saltn), or bis(salicylidene)cyclohexane-1,2-diyldiamine (H2salchn), and the corresponding ZnII complexes [ZnB] (B=Schiff base). The excitation and luminescence spectra of the solution containing [Eu(pta)3] and [Zn(salchn)] exhibited much stronger intensities than those of solutions containing the other [ZnB] complexes. The introduction of a tBu group into the Schiff base was not effective in sensitizing the luminescence of [Eu(pta)3]. The luminescence spectrum of [ZnB] showed a band around 450,nm. The intensity decreased in the presence of [Eu(pta)3], reflecting complexation between [Eu(pta)3] and [ZnB]. On the basis of the change in intensity against the concentration of [ZnB], stability constants were determined for [Eu(pta)3Zn(saltn)], [Eu(pta)3Zn{(tBu)saltn}], and [Eu(pta)3Zn(salchn)] as 4.13, 4.9 and 5.56, respectively (log,, where =[[Eu(pta)3ZnB]]([[Eu(pta)3]][[ZnB]]),1). The quantum yields of these binuclear complexes were determined as 0.15, 0.11, and 0.035, although [Eu(pta)3Zn(salchn)] revealed the strongest luminescence at 613,nm. The results of X-ray diffraction analysis for [Eu(pta)3Zn(saltn)] showed that ZnII had a coordination number of five and was bridged with EuIII by three donor O-atoms, i.e., two from the salicylidene moieties and one from the ketonato group pta. [source] [5-(p -alkoxy)phenyl-10, 15, 20-tri-phenyl] porphyrin and their rare earth complex liquid crystallineJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 2007Miao Yu Abstract Three series of porphyrin liquid crystalline compounds, [5-(p -alkoxy)phenyl-10, 15, 20-tri-phenyl] porphyrin and their rare earth complexes (Tb (III), Dy (III), Er (III), Yb (III)), with a hexagonal columnar discotic columnar(Colh) phase have been synthesized. These compounds were characterized by elemental analysis, molar conductances, UV-visible spectra, infrared spectra, luminescence spectra, and cyclic voltammetry. These compounds exhibit more than one mesophases, which transition points of temperature change from ,33.6 to 16.0,°C, and transition points of temperature for isotropic liquid also increase from 4.9 to 38.2,°C, with increasing chain length. Their surface photovoltage (SPV) response have also been investigated by the means of surface photovoltage spectroscopy (SPS) and field-induced surface photovoltage spectroscopy (EFISPS). It was found that their SPV bands are analogous with the UV-visible absorption spectra and derived from the same transition. Copyright © 2007 John Wiley & Sons, Ltd. [source] Piezospectroscopic Analysis of Interface Debonding in Thermal Barrier CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2000Xiao Peng One of the principal modes by which electron-beam-evaporated thermal barrier coatings fail is via the nucleation of local regions of debonding, which grow and link together until reaching a critically sized flaw for spontaneous buckling and spalling. This progressive-failure mode is used as a basis for analyzing the changes that can occur in photostimulated luminescence spectra that have been recorded from the thermally grown oxide. This process also provides a basis for the quantitative determination of the extent of local damage prior to spalling from an analysis of the shape of the luminescence spectra. [source] Polarization dependences of absorption and luminescence spectra on each crystal face of ,-quaterthiophene and ,-quinquethiophenePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2010Shin Tanaka Abstract Polarization dependence of the absorption spectra (ABS) and the luminescence spectra in ,-quaterthiophene (4T) and ,-quinquethiophene (5T) has been measured directly with near normal incident light on the ab, bc, and ca crystal planes of their thick single crystals (SCs). Vibronic excitons (Frenkel excitons) have been observed on each crystal plane of 4T and 5T. The polarizations of the ABS are consistent with the prediction obtained from the MOPAC calculations of the transition dipole moment directions of the molecules in the SCs. Excited electron relaxes to the lowest excited state which is composed of the LUMO states. [source] Photophysics of J-aggregate microcavitiesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2008P. Michetti Abstract We have developed a model in order to account for the photo-excitation dynamics of J-aggregate films and strongly coupled J-aggregate microcavities. The J-aggregates are described as a disordered Frenkel exciton system in which relaxation occurs due to the presence of a thermal bath of molecular vibrations. The link between the J-aggregate film and the microcavities is obtained introducing a model polariton wavefunction mixing cavity photon modes and J-aggregate superradiant excitons. With the same approach we have calculated both absorption and luminescence spectra for the J-aggregate film and the photoluminescence of strongly coupled organic microcavities. The model is able to explain the organic microcavities fast relaxation dynamics and polariton luminescence following non resonant pumping starting from the excitonic properties of the optically active layer. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Light,matter interaction in finite-size plasma systemsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2007W. Hoyer Abstract It is well known that electromagnetic waves with frequencies below the plasma frequency cannot propagate inside an electron plasma. For plasmas with infinite extensions, this property can be mathematically described by a Bogoliubov transformation of the photonic operators. More generally, the presence of finite-size electron plasmas such as laser-induced atmospheric light strings or metallic nano structures including metamaterials leads to a modification of the light,matter interaction. It is shown how this geometric property can be fully accounted for with the help of adapted mode functions used for the quantization of the electromagnetic field. In addition to the analytical derivations, numerical results for luminescence spectra out of quasi-two-dimensional, planar plasma sheets are presented. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Theoretical study of pressure shift for R line of Cr3+ ion in lanthanum lutetium gallium garnetPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2006Yi-Yang Zhou Abstract The pressure shifts for R line (2E , 4A2 transition) of Cr3+ luminescence spectra in lanthanum lutetium gallium garnet (LLGG:La3Lu2Ga3O12) are studied by a molecular orbital model. The obtained pressure dependence of R line is in qualitative agreement with experiments, this is an attempt to overcome the theoretical difficulty for the R line pressure shifts of Cr3+:LLGG within the crystal-field approximation. The anticrossing model and the assumed nephelauxetic effect for Cr3+ ions in gallium garnets are mentioned. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoluminescence from InGaN/GaN MQWs on sapphire and membranes fabricated by laser lift-offPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004Tongjun Yu Abstract Photoluminescence and Raman scattering spectra of InGaN/GaN MQWs on sapphire and membranes free of substrate fabricated by laser lift-off have been studied. It is observed that photoluminescence peak of 850 °C annealed sample red-shifts from that of as grown sample, while in the case of membrane samples, the luminescence peak blue-shifts when annealed at 700 °C. In Raman scattering spectra, InGaN/GaN MQWs film without sapphire substrate has a lower E2 mode frequency (569.3 cm,1) than that of the films with substrate (570.8 cm,1), which indicates that compressive stress in the films releases partially when the sapphire substrate is taken off. It is believed that the piezoelectric field decrease leads to the blue-shift in luminescence spectra. Compared with the samples with sapphire substrate, the free-standing membranes showed blue-shift of luminescence peak after relatively low temperature annealing, because the piezoelectric field reduced more easily in the films without substrate. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Luminescence spectra in metallic and ferromagnetic GaMnAs/GaAs multilayers: a self-consistent super-cell Kane k.p calculationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2004G. M. Sipahi Abstract We present a self-consistent Kane k.p calculation for obtaining the luminescence spectra of GaMnAs/GaAs multilayers. Our model consists of substitutional Mn ions uniformly distributed in GaMnAs layers of width d1 at a concentration of 5%. The high Mn concentration allows to approximating the density of the magnetic moments by a continuous distribution when treating the magnetic interaction between holes and the localized moment on the Mn++ sites. These DMS layers are assumed to be ferromagnetic, at T = 0 K, metallic, and with a hole concentration equivalent, in bulk, to 1 × 1020 cm,3. The DMS layers are separated by non-magnetic GaAs layers. The magnetization is kept perpendicular-to-the-plane (parallel to the growth direction) by the application of a weak magnetic field, which does not affect the electronic structure directly. The luminescence spectrum is obtained for several numbers of DMS layers in the structure. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Conversion of an electron,hole plasma into a high density excitonic state in ZnO epitaxial thin filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004Y. Toshine Abstract Time-resolved luminescence spectra of an exciton-exciton scattering process and an electron,hole plasma (EHP) were measured in ZnO epitaxial thin films by the optical Kerr gate method. At moderate excitation density below critical Mott density, stimulated emission of luminescence due to the exciton,exciton scattering process (P band) was observed. The P band shows a red shift and spectral narrowing in the first 1,2 ps after the excitation which reflects a thermal redistribution of excitons in the n = 1 excitonic state. On the other hand, at high excitation density above the critical Mott density, stimulated emission of the luminescence due to the EHP was observed. After thermalization of the EHP, the luminescence intensity of the EHP band decreases with time, and the EHP band converts to the P band after ,10 ps through a reverse Mott transition. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A novel calixarene-containing hyperbranched aliphatic polyester incorporated with pendant europium complexesPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2009Jichang Feng Abstract A novel calixarene-containing hyperbranched aliphatic polyester incorporated with pendant europium complexes (H20-Cal-Eu) was synthesized and characterized by FTIR, UV, and element analysis. The polymer H20-Cal-Eu shows a glass-transition temperature (Tg) of 127°C, and a deposition temperature in the range of 280,600°C, as revealed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The investigation on its photoluminescence (PL) properties revealed that the polymer emitted a remarkably strong red luminescence. Furthermore, its half spectral bandwidth of the polymer film is only about 10,nm as determined from luminescence spectra, suggesting that the light is nearly monochromatic. It is proposed that the hyperbranched polymer (HBP) containing rare earth element exhibits great potential as a red light emitting material. Copyright © 2009 John Wiley & Sons, Ltd. [source] Luminescent Excited-State Intramolecular Proton-Transfer (ESIPT) Dyes Based on 4-Alkyne-Functionalized [2,2,-Bipyridine]-3,3,-diol DyesCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2008Gilles Ulrich Dr. Abstract Functionalized 6,6,-dimethyl-3,3,-dihydroxy-2,2,-bipyridine dyes (BP(OH)2) exhibit relatively intense fluorescence from the relaxed excited state formed by excited-state intramolecular proton transfer (ESIPT). Bromo functionalization of (BP(OH)2) species followed by palladium(0)-catalyzed reactions allows the connection (via alkyne tethers) of functional groups, such as the singlet-emitter diazaboraindacene (bodipy) group or a chelating module (terpyridine; terpy). The X-ray structure of the terpy-based compound confirms the planarity of the 3,3,-dihydroxy-bipyridine unit. The new dyes exhibit relatively intense emission on the nanosecond timescale when in fluid solution, in the solid state at 298,K, and in rigid glasses at 77,K. In some cases, the excitation wavelength luminescence was observed and attributed to 1),inefficiency of the ESIPT process in particular compounds when not enough vibrational energy is introduced in the Franck,Condon state, which is populated by direct light excitation or 2),the presence of an additional excited state that deactivates to the ground state without undergoing the ESIPT process. For some selected species, the effect of the addition of zinc salts on the absorption and luminescence spectra was investigated. In particular, significant fluorescence changes were observed as a consequence of probable consecutive formation of a 1:1 and 1:2 molecular ratio of ligand/zinc adducts owing to coordination of ZnII ions by the bipyridyldiol moieties, except when an additional terpyridine subunit is present. In fact, this latter species preferentially coordinates to the ZnII ion in a 1:1 molecular ratio and further inhibits ZnII interaction. In the hybrid Bodipy/BP(OH)2 species, complete energy transfer from the BP(OH)2 to the bodipy fluorophore occurs, leading to exclusive emission from the lowest-lying bodipy subunit. Des composés colorés à base de 6,6,-dimethyl-3,3,-dihydroxy-2,2,-bipyridine (BP(OH)2) ont été synthétisés et présentent une fluorescence relativement intense issue de la relaxation d,un état excité provenant d,un transfert de proton dans l,état excité (ESIPT). La bromation de dérivés (BP(OH)2) suivie d,un couplage croisé catalysé par du Pd0sous-ligandé permet de connecter (par l,intermédiaire de pont alcyne) des groupes fonctionnels comme un groupe émetteur singulet de type boradiazaindacène (Bodipy) ou un module chélatant universel (une terpyridine). Une structure par diffraction aux rayons X a été obtenu avec le dérivé terpyridine, celle ci confirme la planéité de l,unité 3,3,-dihydroxy-bipyridine. Les nouveaux fluorophores possèdent une émission relativement intense avec une durée de vie de l,ordre de la nanoseconde, en solution et à l,état solide à 298,K ainsi que dans un verre à 77,K. Dans certain cas, la luminescence dépend de la longueur d,onde d,excitation, ce phénomène est attribué à (i) l,inefficacité du processus ESIPT, quand trop peu d,énergie vibrationnelle est introduite dans l,état Franck-Condon peuplé directement par la lumière d,excitation (ii) la présence d,un état excité supplémentaire qui désactive l,état fondamental sans passer par un processus ESIPT. Pour certains composés, l,effet de l,addition de sels de Zinc sur les spectres d,absorption et d,émission a été étudié : en particulier, des changements significatifs de fluorescence ont été observés, probablement due à la formation consécutive de complexes ligand/zinc de st,chiométrie 1:1 et 1:2, provenant de la coordination des cations ZnIIpar l,unité bipyridyl-diol, sauf quand une fonction terpyridine est présente. En fait, dans cette dernière espèce le zinc est préférentiellement coordiné par la terpyridine dans un ratio 1:1, et toute coordination supplémentaire de Zinc semble inhibée. Dans le composé hybride Bodipy/BP(OH)2,un transfert d,énergie quantitatif est observé du BP(OH)2vers le fluorophore Bodipy, entraînant une émission exclusive de la sous-unité Bodipy. Composti basati sulla subunità 6,6,-dimetil-3,3,-dididrossi-2,2,-bipiridina (BP(OH)2), variamente funzionalizzati, presentano fluorescenza relativamente intensa da stati eccitati formati attraverso trasferimento protonico nello stato eccitato (ESIPT). Bromo-funzionalizzazione dei composti di tipo BP(OH)2, seguita da reazioni catalizzate da Pd(0), permettono di connettere (con legame alchinico) gruppi funzionali quali il diazaboroindacene (Bodipy) o un modulo chelante (terpiridina) al frammento BP(OH)2. La struttura ai raggi X del composto contenente la terpiridina conferma la planarità dell,unità 3,3,-diidrossi-bipiridina. Le nuove specie presentano intensa emissione nella scala dei nanosecondi, in soluzione fluida ed allo stato solido a 298,K ed in matrice rigida a 77,K. In alcuni casi, la luminescenza dipende dalla lunghezza d,onda di eccitazione: questo fenomeno è attribuito a (i) inefficienza del processo ESIPT, quando non sufficiente energia vibrazionale è introdotta nello stato Franck-Condon a seguito di eccitazione luminosa o (ii) alla presenza di uno stato eccitato addizionale che si disattiva allo stato fondamentale senza passare dallo stato eccitato prodotto attraverso il meccanismo ESIPT. Per composti selezionati è stato anche studiato l,effetto della presenza di sali di zinco sulle proprietà di assorbimento elettronico e di luminescenza: significativi cambiamenti della fluorescenza sono stati osservati, come conseguenza della consecutiva formazione di addotti 1:1 e 1:2 (rapporto molare BP(OH)2/zinco), dovuta alla coordinazione di cationi di ZnIIda parte del bipiridil-diolo, che si verifica in tutti i casi studiati tranne in presenza di una subunità terpiridinica. In quest,ultimo caso, infatti, si forma soltanto l,addotto 1:1, e ulteriore coordinazione di cationi di ZnIIappare inibita. Nella specie ibrida Bodipy/BP(OH)2si verifica un completo trasferimento di energia elettronica dal BP(OH)2 al Bodipy, che porta ad emissione esclusivamente dalla subunità Bodipy, a piû bassa energia. [source] Electronic and Vibrational Properties of Fluorenone in the Channels of Zeolite LCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2004André Devaux Dr. Abstract Fluorenone (C13H8O) was inserted into the channels of zeolite L by using gas-phase adsorption. The size, structure, and stability of fluorenone are well suited for studying host,guest interactions. The Fourier transform IR, Raman, luminescence, and excitation spectra, in addition to thermal analysis data, of fluorenone in solution and fluorenone/zeolite L are reported. Normal coordinate analysis of fluorenone was performed, based on which IR and Raman bands were assigned, and an experimental force field was determined. The vibrational spectra can be used for nondestructive quantitative analysis by comparing a characteristic dye band with a zeolite band that has been chosen as the internal standard. Molecular orbital calculations were performed to gain a better understanding of the electronic structure of the system and to support the interpretation of the electronic absorption and luminescence spectra. Fluorenone shows unusual luminescence behavior in that it emits from two states. The relative intensity of these two bands depends strongly on the environment and changes unexpectedly in response to temperature. In fluorenone/zeolite L, the intensity of the 300 nm band (lifetime 9 ,s) increases with decreasing temperature, while the opposite is true for the 400 nm band (lifetime 115 ,s). A model of the host,guest interaction is derived from the experimental results and calculations: the dye molecule sits close to the channel walls with the carbonyl group pointing to an Al3+ site of the zeolite framework. A secondary interaction was observed between the fluorenone's aromatic ring and the zeolite's charge-compensating cations. [source] Cathodoluminescence spectral mapping of III-nitride structuresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2004R. W. Martin Abstract The application of cathodoluminescence spectral mapping to the characterisation of a range III-nitride semiconductor structures is described. Details are presented of the instrumentation developed to carry out such measurements using an electron probe micro-analyser. The spatial resolution of the luminescence data is ,100 nm. The technique is enhanced by the ability to simultaneously perform X-ray microanalysis and electron imaging. Results are presented from epitaxially laterally overgrown GaN and InGaN/GaN structures using both single-layer SiO2 and multilayer SiO2/ZrO2 masks. Effects of strain and microcavity formation are resolved. Application of the technique to InGaN epilayers shows spatially-dependent shifts in the peak wavelength of the luminescence spectrum which correlate directly with microscopic variations in the indium content. Regions emitting at lower energy and with decreased intensity are shown to have higher InN contents, mirroring equivalent macroscopic observations. Finally the spectral mapping technique is used to analyse the luminescence from micron-scale selectively grown III-N pyramids, indicating possible formation of quantum dots at the sharp tips. (© 2004 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] Growth of InGaN quantum dots on GaN by MOVPE, employing a growth temperature nitrogen annealPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003R. A. Oliver Abstract We have studied the growth of InGaN epitaxial layers on GaN by MOVPE (metal-organic vapour phase epitaxy), and have discovered that nanostructures may be formed if a flat epilayer is annealed in molecular nitrogen immediately after growth. The size and density of the nanostructures are shown to be dependent on the growth/anneal temperature. We demonstrated the quantum dot nature of our nanostructures by performing spatially resolved photoluminescence on samples that had been capped with a layer of GaN, grown at the same temperature as the InGaN epilayer. This revealed narrow, delta-function-like lines in the luminescence spectrum with full width at half maximum (FWHM) limited by the resolution of the spectrometer at 4.2 K. Measurement of the FWHM as a function of temperature revealed significant broadening above 20 K. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||