TO
| Creator | Title | Description | Subject | Date | ||
|---|---|---|---|---|---|---|
| 1 |
 | Vardeny, Zeev Valentine; Gellermann, Werner | Amplified resonant Raman scattering in conducting polymer thin films | Using picosecond pulsed laser excitation, we investigate the optical emission characteristics of poly(2,5-dioctyloxy-p-phenylenevinylene), (DOO-PPV), thin films at high excitation intensities (~1-90 MW/cm2). We observe the presence of amplified resonance Raman scattering in the emission spectra of c... | Amplified resonant Raman scattering; High excitation intensities; pi-conjugated polymers | 1998 |
| 2 |
 | Vardeny, Zeev Valentine | Below-gap excitation of ∏-conjugated polymer-fullerene blends: implications for bulk organic heterojunction solar cells | We used a variety of optoelectronic techniques such as broadband fs transient and cw photomodulation spectroscopies, electroabsorption, and short-circuit photocurrent in bulk heterojunctions organic solar cells for studying the photophysics in ∏-conjugated polymer-fullerene blends with below-gap... | pi-conjugated polymers; Fullerene blends; Below-gap excitations; Bulk heterojunctions; Bulk organic heterojunction solar cells; Photophysics | 2008-07 |
| 3 |
 | Vardeny, Zeev Valentine; Ehrenfreund, Eitan A. | Comment on "Frequency response and origin of the spin-½ photoluminescence-detected magnetic resonance in a ∏-conjugated polymer | In a recent paper, Segal et al. [Phys. Rev. B 71, 245201 (2005)] advanced a new explanation for the dynamics of spin-1/2 photoluminescence-detected magnetic resonance (PLDMR) in films of a rr-conjugated polymer, namely, a soluble derivative of poly(phenylene-vinylene) (MEH-PPV), using a model [dubbe... | Photoluminescence-detected magnetic resonance; PLDMR; pi-conjugated polymers; Poly(phenylene-vinylene); MEH-PPV | 2007-06 |
| 4 |
 | Vardeny, Zeev Valentine | Confined and delocalized polarons in ∏-conjugated oligomers and polymers: a study of the effective conjugation length | We studied optical absorption of polarons in ∏-conjugated oligomers and polymers using the photoinduced absorption technique as well as chemical doping spectra from the literature. We find that the photon energy of the polaron low-energy transition obeys a relationship that depends only on the oli... | Confined polarons; Delocalized polarons; pi-conjugated oligomers; pi-conjugated polymers; Effective conjugation length | 2004-06 |
| 5 |
 | Vardeny, Zeev Valentine | Conjugation-length dependence of spin-dependent excition formations rates in ∏-conjugated oligomers and polymers | We have measured the ratio, r =ơ s/ơT of the formation cross section, ơ of singlet and triplet excitons from polarons in ∏-conjugated oligomer and polymer films, using a spectroscopic technique we developed recently. We discovered a universal relation between r and the conjugation length (CL): ... | pi-conjugated polymers; Conjugation length; Polaron recombination | 2002-04 |
| 6 |
 | Vardeny, Zeev Valentine | Cooperative and stimulated emission in poly(p-phenylene-vinylene) thin films and solutions | We discuss cooperative and stimulated emissions and separate their respective contributions to the emission spectral narrowing in thin films and solutions of poly(p-phenylene-vinylene) derivatives. Whereas cooperative radiation is favored in films with poor optical confinement, directional stimula... | pi-conjugated polymers; PPV; Spectral narrowing | 1998-04 |
| 7 |
 | Vardeny, Zeev Valentine | Directional emission from asymmetric microlaser resonators of ∏-conjugated polymers | A ∏-conjugated polymer film was fabricated into an asymmetric microlaser resonator having a quadrapole deformation with irregular boundaries and a Q factor of 600. At high excitation intensities above the threshold for lasing, we observed multimode laser emission spectra and directional emission a... | Directional emission; Asymmetric microlaser resonators; pi-conjugated polymers; DOO-PPV; poly(dioctyloxy) phenylene vinylene | 2004 |
| 8 |
 | Vardeny, Zeev Valentine | Efficiency enhancement of an organic light-emitting diode with a cathode forming two-dimensional periodic hole array | We fabricated an organic light-emitting diode using a ∏-conjugated polymer emissive layer sandwiched between two semitransparent electrodes: an optically thin gold film anode, whereas the cathode was in the form of an optically thick aluminum (Al) film with patterned periodic subwavelength two-dim... | pi-conjugated polymers; Organic light-emitting diode; OLED | 2005 |
| 9 |
 | Vardeny, Zeev Valentine | Electroabsorption spectroscopy of luminescent and nonluminescent ∏-conjugated polymers | We have measured the quadratic electroabsorption (EA) spectrum of a variety of soluble luminescent and nonluminescent p-conjugated polymer films in the spectral range of 1.5-4.5 eV. The luminescent polymers include MEH and DOO derivatives of poly(phenylene-vinylene), poly(phenylene ethylene), and ... | Electroabsorption spectroscopy; pi-conjugated polymers | 1997-12 |
| 10 |
 | Vardeny, Zeev Valentine | Electromodulation of charge-transfer photoexcitations in pristine and C60-doped conjugated polymers | We study the effect of an electric field of up to 100 kV/cm on photoexcitations in pristine and C60-doped p-conjugated polymers by electromodulated photoinduced absorption (EPA). In EPA, we measure changes in the photoinduced absorption of a polymer film induced by an electric field. The dominant ... | Electromodulation; Charge-transfer photoexcitations; Photoinduced absorption; pi-conjugated polymers; Electromodulation spectroscopy | 1999-04 |
| 11 |
 | Vardeny, Zeev Valentine | Excitation dynamics in single molecular crystals of α-hexathiophene from femtosecond to millisecond | We identify odd- and even-parity states and measure transient photomodulation spectra of Frenkel excitons in a-hexathiophene single crystals. The lowest Frenkel excitons are characterized by a stimulated emission band at ~2 eV and an absorption band at 1.3 eV. Intramolecular internal conversion go... | Excitation dynamics; alpha-hexathiophene; Frenkel excitons; pi-conjugated polymers; Photoexcitation | 2001-04 |
| 12 |
 | Vardeny, Zeev Valentine | Excited-state relaxation in ∏-conjugated polymers | We study ultrafast relaxation processes of odd- (Bu) and even-parity (Ag) exciton states in poly(p-phenylene vinylene) derivatives. The Bu states are studied using a regular two-beam pump-and-probe spectroscopy, which can monitor vibronic relaxation and exciton diffusion. In order to observe the A... | Ultrafast relaxation; Excited-state relaxation; pi-conjugated polymers; PPV | 2002-05 |
| 13 |
 | Vardeny, Zeev Valentine | Experimental determination of the charge/neutral branching ratio η in the photoexcitation of ∏-conjugated polymers by broadband ultrafast spectroscopy | We demonstrate a long-sought reliable method for determining the important branching ratio η between photogenerated charged polarons and neutral excitons in ∏-conjugated polymer films and solutions, using femtosecond transient photomodulation spectroscopy with broad spectral range from 0.14 to ... | pi-conjugated polymers; Charge/neutral branching ratio; Photoexcitation; nu value; Broadband ultrafast spectroscopy | 2007-02 |
| 14 |
 | Lupton, John Mark | Intrinsic room-temperature electrophosphorescence from a π-conjugated polymer | Electrically induced phosphorescence from a poly(para-phenylene) ladder-type polymer is observed for the first time and characterized using time resolved spectroscopy. Short-lived phosphorescence is also observed in gated fluorescence spectra and is found to be quenched reversibly by oxygen. Therm... | pi-conjugated polymers; Electrophosphorescence; Ladder-type polymer; Gated fluorescence spectra | 2002-09 |
| 15 |
 | Vardeny, Zeev Valentine | Laser action in polydialkylfluorene films: influence of low-temperature thermal treatment | We have used a variety of optical probes to investigate the changes occurring upon low-temperature thermal treatment to the emissive properties of dialkyl substituted polyfluorene thin films. We found that the low-temperature-driven morphological changes involving aggregates formation, which are ob... | Laser action; Polydialkylfluorene films; pi-conjugated polymers; Thermal treatment | 1999 |
| 16 |
 | Vardeny, Zeev Valentine | Lasing and stimulated emission in ∏-conjugated polymers | Recent studies of lasing and stimulated emission in luminescent -conjugated polymers performed by our group are presented. Optical properties of cylindrical high- polymer microcavities are discussed. The emission spectra of plastic microring and microdisk lasers are measured and analyzed. Light-emi... | Lasing; Stimulated emission; pi-conjugated polymers; Microcavities; Polymer lasers | 2000-01 |
| 17 |
 | Vardeny, Zeev Valentine | Linear and nonlinear optical spectroscopies of PPV/PPE copolymer semiconductors | We used a variety of picosecond transient and cw spectroscopies to investigate the linear and nonlinear optical properties of films of PPE/PPV copolymer semiconductor. The spectroscopies used include absorption, electroabsorption (EA) and two-photon-absorption (TPA). In addition to the odd parity e... | Linear optical spectroscopy; Nonlinear optical spectroscopy; PPV/PPE copolymer; pi-conjugated polymers | 2005 |
| 18 |
 | Vardeny, Zeev Valentine; Ehrenfreund, Eitan A. | Linear and nonlinear photoexcitation dynamics in ∏-conjugated polymers | Linear and nonlinear recombination kinetics with various lifetime distributions were identified for long-lived photoexcitations in a series of rr-conjugated polymer films using modulation frequency and excitation intensity dependencies of the photoinduced absorption. This includes monomolecular, bim... | Linear photoexcitation; Nonlinear photoexcitation; pi-conjugated polymers; Recombination kinetics | 2003-01 |
| 19 |
 | Vardeny, Zeev Valentine | Magnetic field effects in ∏-conjugated polymer-fullerene blends: evidence for multiple components | We studied magnetoconductance (MC) and magnetoelectroluminescence (MEL) in organic diodes from blends of ∏-conjugated polymers and fullerenes at various concentrations, c. The MC response is composed of several components that depend on the applied bias voltage and c. A dominant positive low-field... | pi-conjugated polymers; Fullerene blends; Magnetic field effects; Magnetoconductance; Magnetoelectroluminescence; MC; MEL; Organic magnetoresistance; OMAR; Organic diodes | 2008-12 |
| 20 |
 | Vardeny, Zeev Valentine | Multiple resonances in microdisk lasers of ∏-conjugated polymers | We have fabricated microdisk lasers from p-conjugated polymers that show multiline emission spectrum upon optical excitation. Using Fourier transform analysis, each emission line is assigned integer to an interger Bessel function that helps to estimate the field distribution inside the photoexcited ... | Multiple resonances; Microdisks; Microdisk lasers; pi-conjugated polymers | 2002 |
| 21 |
 | Vardeny, Zeev Valentine | Nonlinear optical spectroscopy of excited states in polyfluorene | We used a variety of nonlinear optical (NLO) spectroscopies to study the singlet excited-state order and primary photoexcitations in polyfluorene, an important blue-emitting ∏-conjugated polymer. The polarized NLO spectroscopies include ultrafast pump-probe photomodulation in a broad spectral rang... | pi-conjugated polymers; Polyfluorene; Photoexcitations | 2007-03 |
| 22 |
 | Vardeny, Zeev Valentine | Optical probes of ∏-conjugated polymer blends with strong acceptor molecules | We used a variety of optical probes to study the primary and long-lived photoexcitations in blends of polyphenylene-vinylene derivative poly(2-methoxy-5(2'-ethyl)hexoxy-phenylenevinylene) (MEH-PPV) with various concentrations of a strong electron-acceptor molecule 2,4,7-trinitro-9-fluorenone (TNF... | pi-conjugated polymers; pi-conjugated polymer blends; Acceptor molecules; Optical probes; Photoexcitations; MEH-PPV; Electron acceptors; Organic solar cells | 2009-05 |
| 23 |
 | Vardeny, Zeev Valentine | Organic random lasers in the weak-scattering regime | We used the ensemble-averaged power Fourier transform (PFT) of random laser emission spectra over the illuminated area to study random lasers with coherent feedback in four different disordered organic gain media in the weak scattering regime, where the light mean free path, ℓ* is much larger tha... | Organic random lasers; Gain media; pi-conjugated polymers; Opal photonic crystal; RG6; Optical gain; Chicken breast | 2005-01 |
| 24 |
 | Lupton, John Mark | Origin of spectral broadening in amorphous π-conjugated amorphous semiconductors | We present a study of the picosecond fluorescence dynamics of p-conjugated semiconducting organic dendrimers in the solid state. By varying the degree of branching within the dendrons, referred to as the dendrimer generation, a control of intermolecular spacing of the emissive core and therefore o... | pi-conjugated polymers; pi-conjugated semiconductors; Spectral broadening; Solid state; Picosecond fluorescence dynamics | 2002-10 |
| 25 |
 | Vardeny, Zeev Valentine; Ehrenfreund, Eitan A. | Phonon spectroscopy in π-conjugated polymers; the role of the excited electronic states | The Raman active vibrational modes in 7r-conjugated polymers are known to have different frequencies in different types of experiments. The best known examples are the resonant Raman scattering (RRS) and doping or photoinduced absorption infrared active vibrations (IRAV) measurements, in which the s... | pi-conjugated polymers; Phonon spectroscopy; Resonant Raman scattering; ir-active phonons | 1997 |