Ryszard Burzynski

Organic–inorganic heterojunction light emitting diodes based on poly(p-phenylene vinylene)/cadmium sulfide thin films

We report on a solution processed novel electroluminescent heterostructure device consisting of an inorganic semiconductor, CdS, and a polymer emitter, poly(p-phenylene vinylene) (PPV). This configuration provides the advantage of excellent charge transporting properties of an inorganic semiconductor and the high luminescence quantum efficiency of an organic emitter. The electroluminescence spectrum obtained from this hetrostructure device is similar to the emission spectrum of pure PPV. Even with aluminum electrode, we have achieved stable electroluminescence at very low threshold voltage (3 V) and overall quantum efficiency of about 1% in these devices. The device emitted bright electroluminescence radiation (150 cd/m2) at a driving voltage of 10 V under the forward bias condition.

New copolymers for applications as organic LEDs

During the past five years, (pi) -conjugated organic polymers, such as poly[p-phenylene vinylene] (PPV) and polythiophenes, have become attractive alternatives to semiconducting materials as light-emitting diodes. Various approaches to tuning emission wavelength have been proposed, such as controlling the conjugation length by employing polymer oligomers or via steric effects in the fully conjugated polymers, or by using substituent effects to fine-tune the band gap. In the present study, we demonstrate that these features can be designed into copolymeric structures in which (pi) -conjugated emitters of carefully controlled length alternate with various non-emitting flexible spacers which improve solubility and thus processibility. These copolymers display predictable emission characteristics which can also be fine-tuned by incorporation of electronic substituent effects.

Photorefractive properties of a thiapyrylium‐dye‐sensitized polymer composite

The detailed photorefractive properties of a thiapyrylium‐dye‐sensitized photorefractive polymeric composite are presented. The composite contains an ionic thiapyrylium dye, 4‐(4‐dimethylaminophenyl)‐2,6‐diphenylthiapyrylium perchlorate, as a photocharge generation sensitizer, 4‐(N,N‐diethylamino)‐(β)‐nitrostyrene as a second‐order nonlinear optical chromophore, and poly(9‐vinylcarbazole) as a host polymer as well as a charge transporting agent. The electrooptic and photoconductive properties of the composite have been studied and an apparent sublinear dependence of the photoconductivity on the illumination power density has been observed. Both degenerate and nondegenerate four‐wave‐mixing experiments have been carried out and a holographic diffraction efficiency of 1.1% has been achieved in a 160‐μm‐thick film at an external field of 62.5 V/μm. A nonlocal character of the photorefractivity has been established through the asymmetric energy transfer with a gain of 7 cm−1 in a two‐beam coupling experiment....

Large optical birefringence in poly(p-phenylene vinylene) films measured by optical waveguide techniques

Abstract We report here the observation of a large birefringence in an as-cast unoriented film of poly(p-phenylene vinylene), a material that has a large third-order non-linear optical susceptibility. A waveguide technique in TE and TM polarization is used to obtain in-plane and out-of-plane refractive indices at several wavelengths. At 633 nm the measured refractive index values are nTE = 2.085 and nTM = 1.612. No dependence of the in-plane refractive index on the direction of film spreading is found, indicating an in-plane isotropic behaviour. No anomalous dispersion of refractive index is found in the wavelength range 633–1064 nm.

Nonlinear optical processes in a polymer waveguide: Grating coupler measurements of electronic and thermal nonlinearities

We report here the first clear demonstration of intensity‐dependent phase shift due to electronic nonlinearity in a nonlinear polymer waveguide in which propagation distances over 5 cm have been achieved with total attenuation of ∼1.2 cm−1 . Intensity‐dependent coupling angle, intensity‐dependent coupling efficiency, and limiter action behavior have been observed in the polyamic acid waveguide using grating excitation with 400 fs, 80 ps, and 10 ns pulses. A nonlinear grating coupler analysis identifies the subpicosecond and picosecond processes with electronic nonlinearity, but the dominant effect in the nanosecond experiment is due to thermal nonlinearity derived from weak absorptions. The magnitude and sign of n2 of electronic nonlinearity are measured.

Bifunctional chromophore for photorefractive applications

A bifunctional chromophore has been developed which serves as a charge transporting agent as well as a second‐order nonlinear optical compound. The chromophore has been incorporated into an inert polymer to form a photorefractive material when doped with a photocharge generation sensitizer. The dependence of the four‐wave mixing diffraction efficiency, holographic grating writing rate, and two‐beam coupling gain on the chromophore concentration has been studied. The results confirm the photorefractive character of the composite.

Thiapyrylium dye sensitization of photorefractivity in a polymer composite

A new photoretractive polymeric composite operating at near 1R wavelength has been developed which contains an ionic thiapyrylium dye, 4-(4-dimethylaminophenyl)- 2,6-diphenylthiapyrylium perchlorate (TPY, 0.2 wt.%), as a photocharge generation sensitizer, 4-(N,N-diethylamino)-(β)-nitrostyrene (DEANST, ~21 wt.%) as a second-order nonlinear optical chromophore, and poly(9-vinyIcarbozale)(PVK, ~79 wt.%) as a host polymer as well as a charge transporting agent. Samples between 150-300 μm thick are prepared by sandwiching two films precast on 1TO glass substrates. The composite shows a photocharge generation quantum efficiency of 0.3%, a photoconductivity sensitivity of 5.4 × 10 −11 (Ω cm) −1/ (W/cm2) and an electrooptic coefficient (r33) of 4.2 pm/V at an applied field of 62.5 V/μm. The glass transition temperature (Tg) of the composite was determined to be 53°C.

A novel nonlinear optical effect: Stimulated Raman–Kerr scattering in a benzene liquid‐core fiber

By using a long interaction length (250 cm) provided by a liquid (benzene)‐core multimode hollow fiber, we have observed a novel superbroadening stimulated scattering added to the first‐ and second‐order Stokes stimulated Raman scattering lines of liquid benzene. To explain this new effect, a photon‐scattering model of Raman‐induced optical Kerr effect, named as Raman–Kerr scattering, is proposed.

Photorefractive composites with high‐band‐gap second‐order nonlinear optical chromophores

A series of photorefractive composite materials has been developed in which an inert polymer has been doped with second‐order nonlinear optical chromophores, charge transporting agents, and photocharge generation sensitizers. The composites show high photoconductivity, large photorefractive responses, and optical transparency at many wavelengths. Photorefractivity has been demonstrated at wavelengths of 633, 514.5, and 488 nm, with net two‐beam coupling gains.

Novel optical composites: second-order nonlinear optical and polymeric photorefractive materials for optical information storage and processing applications

Recent progress in sol-gel-processed second-order nonlinear optical and photorefractive materials for photonics applications is de- scribed. A number of composites have been prepared in an effort to obtain superior and cost-effective replacements for inorganic crystals. These composites are described followed by a series of measurements indicating the usefulness of these composites in the area of second- order nonlinear optical applications and photorefractive optical informa- tion storage and processing.