Showing papers on "Stokes shift published in 1995"
TL;DR: In this article, InP, GaP and GaInP{sub 2} colloids were synthesized as well-crystallized nanoparticles with bulk zinc blende structure.
Abstract: Quantum dots of InP, GaP and GaInP{sub 2} with diameters ranging from 20-65 {Angstrom} were synthesized as well-crystallized nanoparticles with bulk zinc blende structure. The high sample quality of the InP and GaP QDs results in excitonic features in the absorption spectra. The GaP and GaInP{sub 2} QD colloids exhibited very intense (quantum yields of 15-25%) visible photoluminescence at room temperature. The photoluminescence for InP preparations showed two emission bands: one band in the visible at the band edge of the QD (50 nm Stokes shift), and a second band above 800 nm. The near-IR PL is attributed to deep traps, presumably phosphorus vacancies on the QD surface. This band disappears after activation of particles by controlled addition of etchant. In that case very intense band-edge emission (quantum yield 30% at room temperature and 60% at 10 K) was obtained. The QDs were characterized by TEM, SAXS, AFM, powder x-ray diffraction, steady state optical absorption and photoluminescence spectroscopy, ps to ns transient photoluminescence spectroscopy, and fs to ps pump-probe absorption (i.e., hole-burning) spectroscopy. Results will also be reported on efforts to produce ordered arrays of InP QDs.
314 citations
TL;DR: In this paper, the authors studied the time-resolved fluorescence spectra of the DCM dye molecule in methanol and chloroform using the fluorescence upconversion technique with femtosecond time resolution.
117 citations
TL;DR: In this paper, it was shown that titanate polyhedra containing a short TiO distance show efficient photoluminescence at room temperature if these octahedra are isolated from each other.
81 citations
TL;DR: The structure of the mixed alkaline-earth orthoborate Ba 2 Mg(BO 3 ) 2, a buetschliite derivative, has been established with single-crystal X-ray diffraction methods.
80 citations
TL;DR: In this article, the luminescence of Pb2+ in several calcium borates is reported, and different spectra can be assigned by considering the oxygen coordination, and the splitting of the excitation bands seems to originate from the influence of the crystal field rather than from the Jahn-Teller effect.
Abstract: The luminescence of Pb2+ in several calcium borates is reported. The different luminescence spectra can be assigned by considering the oxygen coordination. The energy levels of the asymmetrically coordinated Pb2+ ion do not seem to be influenced by the orientation of the BO3 triangles, since the absorption and Stokes shift of the emission band are more or less similar for the differently structured borates. The presence of a ‘free’ oxygen ion shifts the excitation and emission bands to lower energies. The splitting of the excitation bands seems to originate from the influence of the crystal field rather than from the Jahn-Teller effect.
58 citations
TL;DR: A reorientation/solvatochromic mechanism, whereby the electrical field reorients the dye molecules so that they experience a change in polarity of their lipid environment is likely to make a significant contribution to both the spectral changes and to the field effect on the acid-base properties of the dye.
58 citations
TL;DR: In this paper, ZnS1−xTex (0≤x≤1) single-crystal alloy films were grown on GaAs and Si substrates by molecular beam epitaxy.
Abstract: ZnS1−xTex (0≤x≤1) single‐crystal alloy films were grown on GaAs and Si substrates by molecular beam epitaxy. Strong photoluminescence in the yellow to blue light region, with room‐temperature external quantum efficiencies of 2%–4% at an unoptimized excitation wavelength of 365 nm, was observed. The enhancement of luminescence was attributed to the presence of Te isoelectronic hole traps in the films. Strong bowing of the band‐gap energy as a function of composition x was also observed, with the minimum near x=0.7. The line width as well as the Stokes shift of the luminescence peak from the band edge were found to increase as Te composition decreases.
54 citations
TL;DR: In this paper, the luminescence properties of CaSO 4 :Pb 2+ (anhydrite), BaSO 4, Pb 2 + -doped anhydrite and PbSO 4 (all barite) are reported.
53 citations
TL;DR: In this article, steady-state optical absorption, fluorescence, and fluorescence polarization data as well as time-resolved results that detail the significant effects of porphyrine tautomerization on the photophysical properties of a metallo-isoporphyrin, zinc 2,3,5, 5,5{prime,7,8,12,18,18-octamethyl-13,17-bis(3-methoxy-3-oxop ropyl) isoporphrin perchlorate (2).
Abstract: Isoporphyrins are porphyrin tautomers with a saturated meso carbon and thus an interrupted {pi} system. We report here steady-state optical absorption, fluorescence, and fluorescence polarization data as well as time-resolved results that detail the significant effects of porphyrine tautomerization on the photophysical properties of a metallo-isoporphyrin, zinc 2,3,5,5{prime},7,8,12,18-octamethyl-13,17-bis(3-methoxy-3-oxop ropyl) isoporphyrin perchlorate (2). Besides the red-shifted, low-energy absorption bands diagnostic of metallo-isoporphyrins, 2 exhibits a large Stokes shift of its fluorescence emission (approximately 600 cm{sup {minus}1}) and an unusually short singlet excited-state lifetime at room temperature (130 {+-} 15 ps), photophysical properties distinctly different from those of the canonical prophyrin tautomers. The only porphyrins to exhibit marginally similar perturbations of their photophysical properties are those with severely nonplanar macrocyles whose {pi} systems are significantly destabilized by the conformational distortions and thus approach the interrupted {pi} systems of isoporphyrins. In addition to providing the first insights into the photophysical consequences of porphyrin tautomerization, the results for the isoporphyrin further document the sensitivity of the fundamental electronic and excited-state properties of porphyrinic chromophores to modulation of their {pi} systems in vitro and, by extrapolation, in vivo as well. 28 refs., 4 figs.
36 citations
15 Sep 1995
TL;DR: In this paper, a picosecond spectroscopic study of the dynamical Stokes shift of fluoroprobe in the lowest excited state in the solvents diethylether and ethylacetate is presented.
Abstract: We report on a picosecond spectroscopic study of the dynamical Stokes shift of fluoroprobe in the lowest excited state in the solvents diethylether and ethylacetate. Time-resolved emission spectra with a time-resolution of approximately 10 ps are presented. The spectra reflect dynamical Stokes shifts of a few thousand wave numbers within 10-100 ps after the pulsed laser excitation. The time-dependent shifts are representative of the solvation dynamics of fluoroprobe in diethylether and ethylacetate.
36 citations
TL;DR: In this article, the photophysical properties of 4-alkyl- and 4alkoxy-4′-cyanobiphenyls with different chain lengths were compared in the dilute solution phase and bulk phases with respect to Stokes shifts and decay times.
Abstract: The photophysical properties of 4-alkyl- and 4-alkoxy-4′-cyanobiphenyls with different chain lengths were compared in the dilute solution phase and bulk phases (crystalline, liquid-crystalline and isotropic) with respect to Stokes shifts and decay times. In solution, highly polar states are formed with decay times around 1 ns and subnanosecond rise times indicative of a molecular rearrangement occurring prior to emission. In the bulk phase, the major proportion of the emission derives from an excimer-type state with a red-shifted spectrum and very long decay time (10–25 ns depending on temperature and chain length). Possible excimer conformations are discussed. An excimer with a twisted geometry (twisted intramolecular charge transfer (TICT) excimer) is excluded by comparison with a bridged biphenyl system (fluorene derivative). The same compound also demonstrates that excited state intramolecular relaxation towards a 90° twist angle is unlikely. In polar solvents, relaxation occurs towards an increased planarity in accordance with the Rapp model. This conclusion is discussed in relation to results from quantum chemical calculations.
TL;DR: In this paper, the energy transfer rate and the time- and frequency-resolved fluorescence of molecular dimers are calculated using the Brownian oscillator model for the solvent, and the results generalize Forster's energy transfer theory to the case when energy transfer and spectral diffusion rates are comparable.
TL;DR: In this paper, the authors measured the ground state hole spectra of cresyl violet in acetonitrile, methanol, and ethanol at room temperature at subpicosecond to picosecond time region.
TL;DR: In this article, the photoexcited electron in EuTe, associated with the photoluminescence band at 1.47 eV, forms the PILMP state, which brings about the large lattice displacement around the 4f hole through the fourf-hole--optical-phonon interaction, producing a large Stokes shift.
Abstract: There has been a controversy over the photoexcited electron state in Eu chalcogenides. This paper examines whether the photoexcited electron in Eu chalcogenides, especially in EuTe, is the self-trapped magnetic polaron (STMP) or the photoinduced localized magnetic polaron (PILMP) bound by the 4f hole produced in the photoexcitation process. The theoretical analysis has been performed for the recent systematic spectroscopic study of Eu chalcogenides [J. Phys. Soc. Jpn. 63, 4616 (1994)]. This paper shows that the photoexcited electron in EuTe, associated with the photoluminescence band at 1.47 eV, forms the PILMP state, which brings about the large lattice displacement around the 4f hole through the 4f-hole--optical-phonon interaction, producing a large Stokes shift. The observed value of the Stokes shift is never explained by the STMP model. It is revealed that the attractive Coulomb interaction between the photoexcited electron and the 4f hole is not weak, which supports the magnetic exciton model in the absorption process. The luminescence band at 1.47 eV in EuSe is understood by the same mechanism. The magnetic polaron effect in EuSe is quite large compared with that in EuTe.
TL;DR: In this article, the luminescence spectra of MoO3 and WO3 at 4.2 K were compared and the differences in terms of the different crystal structures were discussed.
TL;DR: In this paper, the fluorescence properties of two biaryl donor acceptor compounds (4-dimethylamino-4′-cyanobiphenyl (DMACNB) and 4-dimethyl-anilino-1-cyanonaphthalene) were compared in solvents of different polarity and the transient Stokes shifts measured with 30 ps excitation in 1-propanol and 1-hexanol at room temperature show that the charge transfer process is controlled by the dynamics of solvation.
Abstract: The fluorescence properties of two biaryl donor-acceptor compounds (4-dimethylamino-4′-cyanobiphenyl (DMACNB) and 4-dimethyl-anilino-1-cyanonaphthalene (DMACNN)) were compared in solvents of different polarity. Low temperature, steady state spectra were also studied in non-polar and polar media. The transient Stokes shifts measured with 30 ps excitation in 1-propanol and 1-hexanol at room temperature show that the charge transfer process is controlled by the dynamics of solvation. A large decrease in the radiative rate constant as a function of the solvent polarity and as a function of time in 1-hexanol solution was observed for DMACNN, whereas this effect was not significant in the case of DMACNB. These differences have been related to the larger steric hindrance to coplanarity in the phenylnaphthalene derivative with respect to that in the substituted biphenyl.
TL;DR: The spectral properties of bridged polar stilbene, the 2-(4'-((perfluorooctyl)sulfonyl)phenyl)-6-(N,N-dimethylamino)benzofuran (PFSDS-O23*) were investigated in mono-and multilayer Langmuir-Blodgett (LB) films as discussed by the authors.
Abstract: The spectral properties of a bridged polar stilbene, the 2-(4'-((perfluorooctyl)sulfonyl)phenyl)-6-(N,N-dimethylamino)benzofuran (PFSDS-O23†) were investigated in mono- and multilayer Langmuir-Blodgett (LB) films. This molecule forms stable films at the air-water interface which can be transferred to give quartz-supported mono- or multilayers. Absorption and emission spectra of the LB film were compared with those in solution. The dependence of the Stokes shift versus the solvent polarity has been measured to evaluate the extent of charge transfer in the excited state. The observed changes in absorption and emission spectra of the LB films can be explained by an exciton model. The tendency of PFSDS-023 to form H-aggregates was observed even when diluted with C 8 F 17 (CH 2 ) 10 CH 2 OH (1:18). The molecular cross sectional area and the Fourier transform infrared spectroscopy (FTIR) suggest a perpendicular orientation of the dimethylanilino and perfluoroalkyl groups with respect to the substrate
TL;DR: In this article, a solid state reaction of CaCO3, SnO2 and SiO2 was used to obtain the crystal structure of Ca3SnSi2O9 with isolated pairs of edge sharing Sn(IV)O6 octahedra.
TL;DR: In this paper, the interaction of an electronically excited F atom with the neon matrix was investigated using absorption, excitation, and fluorescence spectroscopy, and the emission at 12.80 eV has a detection limited lifetime less than 0.4 ns and is identified as emission from the Ne+F− charge transfer complex.
Abstract: The interaction of an electronically excited F atom with the neon matrix is investigated using absorption, excitation, and fluorescence spectroscopy. Upon vacuum ultraviolet excitation of a neon matrix doped with fluorine atoms, emissions are observed at 12.80, 13.08, and 15.48 eV. The emissions at 13.08 and 15.48 eV have a lifetime of 0.7(0.2) ns and are assigned to the radiative relaxation of the 3s and 3s’ Rydberg F atomic states. The emission at 12.80 eV has a detection limited lifetime less than 0.4 ns and is identified as emission from the Ne+F− charge transfer complex. Absorption and excitation spectra of each of the observed emissions are used to identify the Rydberg absorptions of the F atoms perturbed by the neon matrix at 13.99, 16.27, 16.49, 16.94, 17.22, and 19.02 eV. The Rydberg states belong to ns, ns’, and nd progressions with the same quantum defect as in the gas phase and a blueshift of the vertical ionization energies of 0.8 eV. The Stokes shift of 910 and 790 meV for the 3s and 3s’ sta...
TL;DR: In this paper, the authors have grown InxAlzGa1−x−zAs/InP heterostructure layers of different geometry and composition by molecular beam epitaxy showing very narrow photoluminescence linewidth, small Stokes shift, and high epitaxial quality.
Abstract: We have grown InxAlzGa1−x−zAs/InP heterostructure layers of different geometry and composition by molecular beam epitaxy showing very narrow photoluminescence linewidth, small Stokes shift, and high epitaxial quality For rising z we observe experimental linewidths strongly increasing from 145 meV (InGaAs) to 13 meV (InAlAs) The Stokes shift is found to grow with rising z Several contributions are discussed to explain the measured compositional variation of linewidth and Stokes shift The possibility of arbitrarily combining different material compositions is demonstrated by the growth and characterization of multiple quantum well structures, including possible combinations of ternary and quaternary materials in the wells and barriers
TL;DR: The time-dependent fluorescence Stokes shift of p,p'−cyano thiomethyl diphenylacetylene in three different alcohols at room temperature was measured using time-correlated single photon counting and the spectral reconstruction method as mentioned in this paper.
Abstract: The time‐dependent fluorescence Stokes shift of p,p’‐cyano thiomethyl diphenylacetylene in three different alcohols (1‐propanol, 1‐butanol, and 1‐octanol) at room temperature was measured using time‐correlated single photon counting and the spectral reconstruction method. These measurements were also performed with the probe in 1‐propanol at low temperatures. The observed behavior is consistent with the dynamics of solvation of a polar excited state. As expected, the average solvation time increases with decreasing temperature and is correlated with solvent bulk viscosity down to 180 K. Apparent deviations observed at lower temperatures are attributed to the finite emission lifetime (≊1 ns) of the probe. A significant fast component (<100 ps) is observed in the dynamic Stokes shift even at temperatures close to the freezing point of 1‐propanol. Different mechanisms that could result in such a fast component are discussed.
TL;DR: In this article, a good correspondence has been found between structural characteristics and composition of frontier orbitals, and the strong Stokes shift observed in fluorescence spectra can be attributed to the significant skeletal modifications connected to electronic excitation.
Abstract: Tautomerization of [2,2′-bipyridyl]-3,3′-diol in several electronic states has been studied theoretically by the semiempirical PM3 method. Particular attention has been devoted to the analysis of proton transfer, which can occur through one- or two-step mechanisms. On the grounds of energetic and structural determinations, it is suggested that this latter mechanism is more effective.The strong Stokes shift observed in fluorescence spectra can be ascribed to the significant skeletal modifications connected to electronic excitation. A good correspondence has been found between structural characteristics and composition of frontier orbitals.
29 Sep 1995
TL;DR: A family of indicators has been developed for measuring different analytes, all the indicators being derivatives of the same chemical compound and having identical spectral and lifetime properties as mentioned in this paper, showing an absorption accessible to low-cost light sources, a large Stokes shift, and a long fluorescence decay time.
Abstract: A family of indicators has been developed for measuring different analytes, all the indicators being derivatives of the same chemical compound and having identical spectral and lifetime properties. The indicators show an absorption accessible to low-cost light sources, a large Stokes shift, and a long fluorescence decay time. All indicators can be excited at the same excitation wavelength, monitored at the same emission wavelength, and measured within the same time range. This opens the possibility for a compact lifetime-based instrument for water monitoring.
TL;DR: In this article, the interband absorption of InGaAs/GaAs multiple quantum wells has been studied at 300 K and at 20 K for pressures up to 6 GPa.
TL;DR: In this article, an ultrafast intermolecular electron transfer from electron donating solvent to an excited dye molecule was found, where a temperature-dependent nonexponential time dependence was observed in aniline, and a temperature independent single exponential process for Nile blue (160 fs) and oxazine 1 (260 fs) was observed for N,N-dimethylaniline.
TL;DR: In this article, the Stokes shift, the degree of polarization and the quantum yield of poly(phenylene-arylvinylene)s were investigated in tetrahydrofuran solution and polystyrene films at room temperature.
Abstract: Stationary polarized fluorescence spectra of poly(1,4-phenylene-1-phenylvinylene), poly(1,4-phenylene-1,2-diphenylvinylene) and poly(1,4-phenylene-1,2-bis(4-phenoxyphenyl)vinylene) in tetrahydrofuran solution and in polystyrene films were recorded at room temperature. In these matrices, different behaviour is found concerning the Stokes shift, the degree of polarization and the quantum yield; it is interpreted as a viscosity induced effect. The commonly accepted model of a conjugated polymer chain to consist of independent segments of various length should not be applied to the poly(phenylene-arylvinylene)s studied in this work.
TL;DR: In this paper, the optical properties of ABCl 3 :Mn 2+ crystals in the 300-10 K temperature range are investigated in terms of slight differences in the Mn-Cl distance.
Abstract: The optical properties of ABCl 3 :Mn 2+ crystals are investigated in the 300-10 K temperature range. The variation of the peak energy and the Stokes shift along the series are explained in terms of slight differences in the Mn-Cl distance. The local structure around the Mn is determined by correlating optical spectroscopy and EXAFS techniques. Interestingly, the thermal shift of the 6 A 1g → 4 T 1g excitation band is much smaller than that experienced by the corresponding emission band. This behaviour is explained by the phonon assisted mechanism involve in these transitions. The influence of the structural phase transition of the CsCaCl 3 :Mn 2+ at Tc = 95 K upon the thermal band shift is also analysed.
01 Nov 1995
TL;DR: In this article, site-selective fluorescence spectra have been measured to investigate the origin of the polaronic contribution to charge transport in 4-[bis(4-ethylphenyl)amino]phenyl.
Abstract: Site-selective fluorescence spectra have been measured to investigate the origin of the polaronic contribution to charge transport in 4-[bis(4-ethylphenyl)amino]phenyl-N,N,N′,N′-tetrakis(4-ethylphenyl)-[1,1′:3′1″-terphenyl]-4,4″-diamine doped poly(styrene). The spectra feature an unusually large Stokes shift of σ = 750 cm−1 and remain broad over the entire range of excitation energies. This is a clear indication of a torsional mode of relaxation that can account for the polaronic contribution observed in charge transport experiments.
TL;DR: In this article, the spectroscopic properties of the pyridine-based polymer poly(p−pyridyl vinylene p− phenylene vinylene) (PPyVPV) are examined.
Abstract: The spectroscopic properties of the pyridine-based polymer poly(p−pyridyl vinylene p− phenylene vinylene) (PPyVPV) are examined. The emission of PPyVPV in solution has small intrinsic Stokes shift with some vibronic structure. In contrast, emission from thick film samples is featureless, with a strong redshift of ~0.5 eV versus solution. We attribute these observations to the formation of aggregate states in film samples. Time−resolved photoluminescence measurements are in accord with the diffusion of excitons to the aggregate sites. Photoinduced absorption also originates from excitons in aggregate states.