The emission color stability of poly(fluorene) derivatives upon thermal annealing or passage of current in an electroluminescent device is affected by the polymer molecular wight, the structure of the main chain polymer unit and particularly by the polymer chain end substituents. Proper attention to these features leads to colorfast blue emission in both photo and electroluminescence. Furthermore, the spectral emission characteristics can be tuned by the incorporation of various comonomers. Preliminary single layer device studies validate the potential utility of poly(fluorene) homo and copolymers for OLED applications.

Thermally stimulated luminescence has used to directly measure the trap states in intrinsic Alq₃ and Alq₃ doped with coumarin 6. For Alq₃ doped with coumarin 6, we observe an increase in the trap energy from 0.25eV for undoped Alq₃ to 0.32eV for doping concentrations as high as 2 percent. The origin of these trap states may be related to the relative energy level alignment between the Alq₃ host and coumarin dopant. Using UV photoemission spectroscopy, we have measured the solid state energy alignment of the highest occupied molecular orbitals between Alq₃ and coumarin 6. Finally, we report I-V curves for single layer devices as a function of doping with Al/LiF top and bottom contacts. The charge transport shows the trap states induced in the Alq₃ films due to the presence of the coumarin 6 molecules decrease the carrier mobility and increase the energetic disorder. These results can be directly observed from the measured I-V curves.

We report on organic electroluminescent devices based on Al cathode with luminous efficiency of 20 lm/W and external quantum efficiency of 4.6 percent. When pulsed in air at room temperature and without any encapsulation, high peak brightness of 4.4 X 10⁶ cd/m² and high efficiency of 4.4 cd/A are obtained. In contrast to current belief, we demonstrate that device quantum efficiency can be increased by tuning the ionization potential of the hole-transport moieties. The high efficiency and peak brightness reported here with Al cathode are encouraging for the manufacturing of stable devices and the development of electrically injected organic lasers.

A new luminescent copolymer containing three functional moieties was prepared. It possesses high thermal stability, good electrochemical reversibility, and good thin film- forming ability. Electrical characterization of a two-layer diode device based on the structure of ITO/CuPc/TPDPQ-FPQ/Al showed excellent electroluminescence performance.

We present a study of electrical transport in organic light emitting diodes using a 1D drift diffusion model. This model includes bipolar transport, charge injection and electron trapping on the same footing. As input we have mobilities, doping densities typical of organic semiconducting devices, and barrier heights taken from internal photoemission measurements. Charge density, trap filling, field, potential and recombination profiles in addition to current-voltage characteristics are provided by the mode. We have obtained result for two-layer organic devices, examining the influence of contacts and of traps on the current-voltage characteristic. The density of filled traps is determined by the position of the quasiFermi level with respect to the trap energy levels, and this changes with position and applied bias. The quasiFermi level profile is sensitive to both the type of contact and the doping density. Traps at a single energy level, and with exponential distributions with respect to discrete energy levels have been considered. We see an injection limited current at low biases and bulk limited transport at higher biases with a trap limited current contribution.

We discuss the photovoltaic and electroluminescence properties of three groups of optoelectronic devices with the following organic materials: (A) single layer devices made of para-hexaphenyl (PHP), pristine methyl-substituted laddertype poly-para-phenylene (mLPPP) and N-(2,6- Diisopropylphenyl)-N'-octylterrylene-3,4,11,12-tetracarboxdiimide- (DOTer) sandwiched between ITO and Al electrodes, (B) mLPPP blended with TiO-phthalocyanine (TiO-Pc) and an aromatic macromolecule, (C) multilayer devices consisting of differently arranged layers made of mLPPP, PHP and DOTer. The motivation for these experiments is the optimization of either charge transfer or energy transfer from one molecular to its neighbor molecule. In order to obtain high photocurrents for photovoltaic applications it is favorable to use a combination of a polymer with electron donor properties and an organic substance with high electron affinity, which provides efficient charge transfer resolution in the creation of polarons. In particular we investigated the influence of the location of the photoactive region on the shape and magnitude of the photocurrent action spectra by performing experiments under electrical and optical bias for different excitation conditions. The best photovoltaic yields were obtained for hetero-structure devices.

Cathodes made with Al-LiF or Al-CsF composites are found to enhance the performance of organic light-emitting devices. With a composite cathode, devices based on an organic bilayer structure have shown lower operating voltage, higher efficiency and better forward light output than devices with LiF/Al, Mg or Al cathode. Unlike devices with Al and Li alloy cathode, OLEDs with composite cathode can be made with good reproducibility.

Using x-ray and UV photoemission spectroscopy (XPS and UPS), we have investigated the early stages of the interface formation between metals, namely Al and Ca, and tris-(8- hydroxyquinoline) aluminum (Alq₃). Both interfaces show signs of reaction between the metal and Alq₃. However, the detailed behaviors of the two interfaces are very different. In the case of Al/Alq₃ interface, the metal was found to react preferentially with the quinolate oxygen as soon as it was deposited onto Alq₃. No evidence of reaction with the carbon was found. Unlike with Ca, little interaction between Al and nitrogen of the pyridyl was observed. UPS spectra show a quick disappearance of the Alq₃ features as early as 0.7 angstrom of Al deposition, and also suggest the formation of a gap state induced by Al. In the case of Ca/Alq₃, the interface is characterized by a staged interface reaction: for low Ca coverages, negatively charged Alq₃ radical anions are formed by electron transfer from the Ca. The emergence of new states in the energy gap is observed in the UPS spectra. At higher overages, the Ca reacts with the phenoxide oxygen resulting in the decomposition of the Alq₃ molecule.

We present simulations of optical propagation in cholesteric liquid crystal (CLC) films and find a stop band in which the wave is evanescent and the density of states is zero. Sharp structure is found in the calculated transmission spectra near the band edge. This corresponds to enhanced residence times and lower group velocities, as well as to significant enhancements of the energy density and of the density of states within the samples. These simulation are consistent with our measurements of suppressed emission within the stop band and of enhanced emission at the band edge for dye molecules doped into CLCs. We also observe spatially coherent emission from the CLC sample with narrow spectral lines at the edge of the stop band and a distinct threshold behavior for the coherent emission. The results of computer simulations together with observations of emission and lasing demonstrate that the optical properties of CLCs, including laser action at the modes closest to the band edge, are consequences of its band gap structure. The compact nature of these structures and the ease with which they ca be fabricated suggest that they may be useful for producing integrated lasers and photonic devices.

Multimode spirobenzopyran (SP) doped PMMA channel waveguides have been fabricated and one- and two-photon absorption induced photochromic reactions have been demonstrated in these waveguides. Bleaching of SP was performed by coupling a 0.75-mW, 543nm beam into these guides. Two-photon absorption based coloring was demonstrated using two counterpropagating pulses, one at 1064 nm and the other at 532 nm. We measured the coupling efficiency to be 0.168, which gave intensities inside the guide of 10.494 GW/cm² and 7.765 GW/cm² for the IR and the green beams, respectively. The ability to shift the colored spot via pulse delay in the counterpropagating pulse scheme was also demonstrated by moving a colored spot by approximately 30 micrometers . Finally, two-photon induced fluorescence was observed by exciting the waveguide with a single 1064-nm beam at an intensity of approximately 10 GW/cm².

We have performed optical Kerr effect measurements on methyl methacrylate (MMA)/nitrobenzene (NB) solutions. By measuring the string of the Kerr signal as a function of the concentration of nitrobenzene we have determined the relative value of the effective third-order susceptibility of MMA to that of nitrobenzene to be "formula available in paper"

A new series of highly efficient, chemically and thermally stable nonlinear optical chromophores have been developed by using a 2-phenyl-tetracyanovinylbutadienyl group as the electron acceptor for a series of dialkyl- or diphenyl-amino substituted thiophene stilbenes. Excellent tradeoffs among absorption, molecular nonlinearity and thermal stability were achieved. Electro-optic polymers based on the guest/host systems and covalent attachment of chromophores onto high temperature polyquinoline backbones demonstrate high E-O activities and good optical, electrical and mechanical properties.

Substantial enhancement of the electro-optic (EO) coefficient of NLO films through optimization of host properties and local chromophore environment is discussed. The EO coefficient was determined for common electro-optic chromophores disperse Red 1 (DR1) and 4-(dicyanomethylene)- 2-methyl-6-(4-dimethylaminostryl)-4H-pyran (DCM) doped in poly(styrene) (PS), poly(2-vinyl pyridine) (P2VP), poly(methyl methacrylate((PMMA), poly(cyclohexyl methacrylate), and styrene-methyl methacrylate copolymers. The r₃₃ varied as much as tow orders of magnitude in this series. Resonance enhancement and local field effects account for 20-25 percent of this variation. The remainder is attributed to intermolecular interactions. Electronic and IR spectroscopy revealed the presence of specific secondary interactions between chromophore-host and chromophore- chromophore. These influence the molecular miscibility and thus alter the effective chromophore concentration and therefore the EO coefficient. Additionally, synergy between the chromophore and a field-responsive host facilitates chromophore alignment. A combination of these effects observed in a DR1-P2VP system leads to an enhancement in r₃₃ by greater than 70 percent with respect to a comparable DR1-PMMA system. An ultimate EO coefficient of 15 pm/V for a 25 wt percent DR1-P2VP system was obtained. These results demonstrate the potential associated with modification of guest-host interactions for the development of highly nonlinear, stable EO polymer systems.

An analysis of the design and function of multi-layer electro-optic (EO) device structures is presented. Some alternate methods of enhancing electro-optic capabilities of existing, well-studied EO materials are investigated. Through analysis of the electronic and linear optical properties of these components, some possible enhancements have been demonstrated. Experimental and theoretical studies have shown that the relative conductivity and electrical properties of the cladding and guiding layers play a crucial role in the function of electro-optic, guided wave devices. The addition of relatively conductive cladding layers in a device structure has been shown to reduce external poling voltage and delay catastrophic breakdown at high effective poling fields, thus enhancing the achievable EO coefficients and reducing the necessity for high poling voltages. Similarly, material studies have also indicated that the incorporation of a thin interplay between guiding and cladding layers can lead to enhanced guiding and poling in electro-optic guided wave devices. Thus modifications of the non-active components in existing device structures are shown to enhance both waveguide function and EO characteristics of these polymer guided-wave devices.

Acentric films of stilbazolium-substituted polyepichlorohydrin (SPECH) and poly(sodium 4- styrenesulfonate) (PSS) were formed using alternating polyelectrolyte deposition (APD) on hydrophobic glass substrates. APD is a layer-by-layer technique for the formation of polymer films by alternately immersing a substrate in aqueous solutions of a polyanion and a polycation. APD provides precise control of the overall film thickness that through automated processing may exceed a thousand layers. The peak maximum UV-visible absorbance in transmission through the SPECH/PSS films was linear as a function of the number of bilayers. Second harmonic generation (SHG) was used as a tool to indicate acentric order to polarizable side-chain chromophores within the APD films. The SHG exhibited the expected quadratic intensity increase with film thickness after 30 bilayers had been deposited. During slow temperature ramping of the SPECH/PSS APD films on hydrophobic glass, in situ SHG measurements revealed that 90 percent of the polar order is retained at temperature well over 120 degrees C. The additional minima in the Maker fringe data, created by interference of the second harmonic waves generated at the two sides of a double-coated substrate, were found to go to zero, which is indicative of high quality films. The observed high thermal stability of the polar order makes the APD films attractive for device applications.

We present an innovative approach for fabricating a polarization modulator, which outputs light alternating in time between left- and right-hand circular. The aim is to replace bulky and expensive photoelastic, liquid-crystal, or inorganic-crystal polarization modulators for certain applications. We use a single-mode polymer waveguide, where a controllable amount of birefringence via the electro-optic effect adjusts the output polarization. It has a very small mass, low power consumption, and very compact size. Other desirable attributes are its use of no moving parts, low voltages, and a single high-speed voltage source. The wavelength of operation is adjustable from 700 to 1600 nm. Furthermore, it can operate at arbitrary frequencies up to the GHz range as compared to the KhZ operating frequencies of photoelastic and liquid-crystal modulators. We show how to overcome the problem of different TE an TM mode amplitudes in polymer waveguides and how to ease the fabrication and packaging tolerances. We present some performance data on a polymer waveguide that outputs circularly polarized light.

The mobility of dye molecules in a polymer matrix was investigated by use of electroabsorption and dielectric relaxation spectroscopy. The electroabsorption spectroscopic method is selective to the relaxation processes of the chromophores embedded in a matrix. The technique can be used to determine the fast relaxation processes at higher temperatures which are not observable in time domain as well as for observation of slow processes below the glass transition point.

Efficient photorefractive polymers hold great potential for optical data processing and storage and so have been a topic of intense investigations in recent years. Materials with nearly 100 percent diffraction efficiencies have been developed, but these have been generally characterized by much slower response than their less efficient inorganic counterparts. In this report, we describe a 4-ms initial rise-time using a visible-transparent chromophore in a PVK- based polymer of T_g equals 39 degrees C for 48-V/micrometers bias projected along the grating vector and 250-mW/cm² writing beams. This fast component consistently accounts for 90 percent of the steady-state response and is analyzed as a function of bias field. We also present transient ellipsometry measurements of an orientational response significantly faster than the grating development, suggesting that chromophores alignment sped does not limit transient grating formation. We describe the role of such underlying property measurements in understanding photorefractive transient behavior, and prospects for further improvements.

The local field within a reorientational photorefractive polymer composite has been estimated to be 2.2 times the applied poling field. Using a transmission ellipsometric technique the birefringence within a pulsed photorefractive polymer material has been measured as a function of applied field. The birefringence at an internal poling field of 110 Vmicrometers ^-1 is 4 X 10^-3. By equating the sum of the poling field and the space-charge field formed within a hologram to the birefringence dependency on field and the holographic contrast obtained in a four wave mixing experiment, the amplitude of the space-charge field has been found. Its values are between 7.8 and 15 Vmicrometers ^-1, depending on the ratio of reorientation and the Pockels contributions to the birefringence. In this regime the holographic contrast is limited by the trap density which is found to be between 7.4 X 10¹⁵ and 15.7 X 10¹⁵ cm^-3.

We have developed hybrid organic-inorganic materials based upon the incorporation of nonlinear chromophores in a rigid amorphous inorganic matrix. Functionalized thin films have been prepared using the sol-gel route allowing for mild synthesis conditions. Push-pull chromophores were either incorporated as guests or grafted on a silica based backbone via a spacer. Orientation of the dipolar chromophores within the materials was performed using the Corona technique. By playing on the structure of the push-pull chromophores and on its orientational stability inside the matrix, functionalized materials with large electro-optic coefficients and excellent stability have been designed. By combining both appropriate push-pull chromophores and photoconductors grafted on the matrix, materials showing interesting photorefractive properties can be obtained without requiring the application of an external electric field. Both the presence of a strong internal field in the poled materials and the occurrence of photo-assisted orientational birefringence plays a significant role.

A pre-requisite to obtain polymers with a large photorefractive response is to design non-linear optical chromophores with a large figure of merit. This figure depends on the glass transition temperature of the material. We present a theoretical investigation that shows which are the important molecular parameters that control the magnitude of the figure of merit either in a low-T_g or in a high-T_g polymer. Derivation of the figures of merit for various push-pull molecules show a molecular engineering strategy can be successfully implemented to yield very large figures of merit. This approach is supported by an experimental investigation based on electro-optical absorption measurements.

We demonstrated efficient and photostable laser action in graded index polymer fiber lasers doped with organic dyes such as Rhodamines, Perylenes and Pyrromethenes. Slope efficiency of 47 percent and output of 2.6 mJ have been obtained with a Rhodamine 6G-doped fiber laser. Moreover, we encapsulated rare earth ions to incorporate them into polymer matrices and studied spectroscopic properties of europium chelates in polymer hosts. Superfluorescent polymer fiber sources based on Eu chelate-doped polymer optical fiber was demonstrated.

Cylindrical PMMA filters with core regions doped with spirobenzopyran molecules have been fabricated. Spirobenzopyran is a photochromic molecule with two forms: spiropyran and merocyanine. In the fibers, one state could be reverted to the other either by a photo-initiated reaction or by thermal excitation. The fluorescence from the merocyanine form could be generated by exciting the core with a 543nm laser. For spirobenzopyran, higher temperatures favor the reaction form spiropyran form to merocyanine form, hence as temperature increases the merocyanine from concentration in the core increase causing the fluorescence intensity to increase. It was observed that the fluorescence increased fairly linearly over a certain range and started rolling off as the temperature approached to 60 degrees C. Refractive index and material dispersion characteristics of SP/PMMA was also measured. Fluorescence generation in the core by two-photon absorption from 40 ps pulses at 1064 nm has been demonstrated. The energy of the pulses was 1.8 uJ, which gave a peak intensity of 5GW/cm² in 33um core. A portion of the emitted fluorescence was guided to the end of the fiber and a portion of it escaped the cladding and radiated into the air.

A simple casting film of Poly(6-[4-(4- cyanophenyl)diazenylphenyl oxy] hexyl methacrylate) (PM6ABCN) was made on an untreated surface of a glass substrate and adopted as a typical sample to study photoinduced orientation of azobenzene liquid crystalline side chain homopolymers. Below Tg and after irradiation of light at 366 nm, 400 nm, and 436 nm, respectively, the same;l shows different UV spectra which can give an expedition on the steady state of the photoinduced orientation. Under various conditions photoinduced orientation of PM6ABCN was examined, and results show that the orientation process is not only dependent on the light strength, but also on the temperature and the wavelength of polarized light used. The maximum extent of orientation below Tg can be obtained within 100 s under irradiation of polarized light of 20 mW/cm² at 400 nm, and irradiation at 366 nm causes a lower extent of orientation than that by irradiation at 400 nm and 436 nm because relative more cis isomer was produced in the steady state.

Phenanthrenequinone (PQ)-doped poly(methyl methacrylate) (PMMA) is a photopolymer holographic recording material that can be made in large thicknesses and does not exhibit any shrinkage. Hologram are made permanent by a post-recording diffusion amplification process. PQ-doped PMMA thus exhibits may properties which make it an ideal candidate as a high- density read-only holographic data storage medium. Recently we reported the holographic recording characteristics of phenanthrenequinone (PQ) doped PMMA. We now demonstrate the holographic storage of binary data in this material. Shift multiplexing is used to store multiple holographic data pages in millimeter thick material samples. Each data page consists of a random array of binary 40 micron pixels. Recording is performed near the Fourier transform plane of the data mask, allowing high bit-densities to be achieve.d The signal to noise ratio of stored data pages is used as an indication of hologram quality and data integrity. Bit density limitations are discussed with respect to the current performance of the recording material.

Bacteriorhodopsin (BR) films with dimension of 100 mm X 100 mm have been developed for applications in non- destructive testing. Films made from the photochromic retinal protein BR have been successfully employed in a variety of optical applications. Among them holographic interferometry for non-destructive testing which is one of the applications where the aperture of the BR-films used for recording plays an important role. The BR-films available earlier had an aperture of about 2/3 inch. Due to this limit size it was necessary to focus the light scattered from the object under investigation to the BR-film by means of lenses which in turn limit the optical resolution of the whole system. Now BR-films with a more than 50-fold larger are have been developed which allow lensless recording of the holograms. The optical quality of the films, in particular the spatial homogeneity of their optical density and their light sensitivity, is constant over the full aperture within a few percent. Applications of this new type of BR-films in non-destructive testing of ceramic parts are presented.

The characterization of monomode passive polymer optical devices fabricated according to the POPCORN technology by methods originated from electron, ion and optical spectroscopy is summarized. Impacts of observed waveguide perturbations on the optical characteristics of the waveguide are evaluated. In the POPCORN approach optical components for telecommunication applications are fabricated by photo-curing of liquid halogenated (meth)acrylates which have been applied on moulded thermoplastic substrates. For tuning of waveguide material refractive indices with respect to the substrate refractive index frequently comonomer mixtures are used. The polymerization characteristics, especially the polymerization kinetics of individual monomers, determine the formation of copolymers. Therefore the unsaturation as function of UV-illumination time in the formation of halogenated homo- and copolymers has been examined. From different suitable copolymer system, after characterization of their glass transition temperatures, their curing behavior and their refractive indices as function of the monomer ratios, monomode waveguides applying PMMA substrates have been fabricated. To examine the materials composition also in the 6 X 6 micrometers ² waveguides they have been visualized by transmission electron microscopy. With this method e.g. segregation phenomena could be observed in the waveguide cross section characterization as well. The optical losses in monomode waveguides caused by segregation and other materials induce defects like micro bubbles formed as a result of shrinkage have been quantized by return loss measurements. Defects causing scattering could be observed by convocal laser scanning microscopy and by conventional light microscopy.

Photo-induced birefringence is proposed as a tool for mode- control applications in integrated optical devices, such as waveguides, fibers, etc. Various geometries of photo- exposition are theoretically considered for the examples of a plane waveguides. Analytical solutions are obtained that provide information about the resulting polarizational behavior of the guide. The presence of birefringent Bragg gratings is then considered and conditions are identified to obtain polarization insensitive spectral filters.

The polarizability and first and second hyperpolarizabilities of several 4,4'-disubstituted trans- stilbene (tSB) derivatives, which include the NO₂ group as an acceptor (A) and several lithium containing donors (D) have been computed. Ab initio theory using a 6-31G basis set at the SCF and MP2 levels has been sued to optimize the structure of tSB and the disubstituted derivative which includes the NO₂ (A) and the NLi₂ (D). Their polarizabilities and hyperpolarizabilities have also been computed at the SCF level. MP2 theory has been used to assess the effect of correlation on the largest polarizability and second hyperpolarizability components of the above compounds. The preset results, together with our recent work show that the second hyperpolarizabilities of some lithiated derivatives depend quite a lot on the molecular geometries and lithiation leads to a big increase of the hyperpolarizabilities of the resulting derivatives. This finding suggests that at lest some of the lithiated derivatives are very likely to be useful for non-linear optical applications.

In the field of organic semiconductor devices, such as electroluminescent diodes or photovoltaic cells, a rectifying junction is mandatory to improve their efficiency. In order to build single polymer film photovoltaic cells, we realize an equivalent distributed p-n junction in a polymeric monolayer. For this purpose, we propose an inter-disciplinary principle derived from the application of nonlinear optical techniques to the technology of polymer semiconductors. We give experimental evidence that molecular rectification induced in an oriented amorphous polymer bearing polar chromophores improves efficiency of polymeric semiconductor device such as photovoltaic cells. Orientation is performed through DC- field ordering of the polar molecules contained in the polymer. Second harmonic generation is used as a probe of the molecular order and permits optimization of the sample orientation parameters, i.e., orientation-field, sample temperature, poling duration and cooling conditions to achieve the largest stable orientation. Additionally, to establish a model which describes charge injection and transport through such device, we propose to use Solid Electric Field Induced Second Harmonic Generation (SEFISHG) as an in situ internal field measurement technique. In this way, before orientation of the molecules, SEFISHG provides the electron work function difference between the two electrode materials, and after orientation, SEFISHG permits the measure of the internal field stored in the structure.