S. Jeglinski

Electroabsorption studies of undoped C60 thin films

Abstract Electroabsorption spectra have been measured for undoped C 60 thin films at 80 and 300 K in the spectral range 1.76 to 5 eV. Absorption and thermal modulation spectra have also been obtained. The electronic energy levels of C 60 are reviewed, and the electroabsorption spectra are discussed in terms of the Stark effect on energy levels of A g , H g and T u symmetries.

Electrically Symmetric Poly(Phenylene Acetylene) Diodes

Abstract A diode has been fabricated with poly(phenylene acetylene) [PPA] as the electroluminescent polymer. The device exhibited an unusual symmetric (positive and negative bias) I-V characteristic and electroluminescent output. These experimental results are discussed in terms of tunneling of electrons and holes via localized states.

Studies of photoexcitations in C70 by optically detected magnetic resonance

Abstract Photoexcitations in C70 both as a dispersion in polystyrene (PS) glass and as films produced by evaporation, have been studied by photomodulation, photoluminescence and their respective versions of optically detected magnetic resonance. In C70: PS glass at 4 K we observed metastable triplet excitons with a distribution of lifetimes and a correlated distribution of magnetic powder patterns. In C70 films, on the other hand, in addition to triplet excitons we observed photogenerated charged excitations with spin 1 2 and a correlated photoinduced electroabsorption; we identify the charged excitations as C∓70.

Electroabsorption and Charged-Excitation Spectroscopy of II-Conjugated Polymers

Abstract Electroabsorption (EA) and photoinduced absorption excitation (PAE) spectra for charged excitations have been measured for luminescent [poly(phenylene acetylene), PPA] and nonluminescent (polydiethynyl silane, PDES) π-conjugated polymers at 80K, over the spectral range from 1.5 to 4 eV. Based on these measurements, a discussion of the locations of the singlet 1BU and Ag states is presented, as well as an analysis of the first- and second-derivative nature of the EA lineshapes. It is argued that luminescence (or lack of) in these polymers depends on the location of an Ag state in close proximity to the 1Bu state.

Electroabsorption in polydiethynylsilane and soluble trans-(CH)χ

Abstract Electroabsorption spectra have been measured for polydiethynylsilane, PDES, and soluble trans -polyacetylene, (CH) χ , at 300 K in the spectral range 1.3 to 2.5 eV. Absorption and thermal modulation spectra are also obtained for the two materials. For both materials, the second derivative of absorption compares well with the electroabsorption spectrum. The electroabsorption spectra, however, are discussed in terms of the Stark effect on energy states of A g and B u symmetry. The absorption second derivative and the electroabsorption spectra are used to estimate the Stark shift of the 1B u exciton.

Optical probes of c60 thin films

Abstract Data obtained from thin films of C60 using the techniques of absorption, photoluminescence, resonance Raman scattering, electroabsorption, and transient photomodulation are presented to develop an understanding of the energy levels and their dynamics in this fullerene solid.

Photomodulation spectroscopy of soluble polyacetylene

Abstract Photoexcitation of soluble polyacetylene has been investigated by both steady-state and transient picosecond photomodulation spectroscopies. The steady-state photoinduced absorption spectrum shows the usual band at 0.5 eV assigned to charged solitons, while the neutral soliton absorption band is concealed under the strong photoinduced electroabsorption. The picosecond spectrum confirms the anomaly in the high-energy photoinduced absorption band, which appears to be much weaker, broader and more strongly temperature dependent than in regular Shirakawa polyacetylene films. This is correlated with the particular sample morphology and the defect-mediated stabilization mechanism of the neutral photoexcitations.

Optical excitations of poly(3-butylthiophene) and high electron affinity substituted poly(3-butylthiophene)

Abstract We have characterized the long lived photoexcitations in thin films of poly(3-butylthiophene) [PBT] and co-polymers made of PBT and acceptor substituted PBT, using photo-induced absorption (PA) and optically detected magnetic resonance PA (PADMR) spectroscopies. The PA spectra reveal two main absorption bands; one at 1.4-1.7 eV, which is composed of contributions from both S=1 and S = 1 2 species, and another at 0.5 eV which is due to S = 1 2 charged species. Our results are explained within a picture where the S=1 species are triplet excitons and the S = 1 2 species are photogenerated polarons.