This pdf file contains the Front Matter associated with SPIE Proceedings Volume 7722, including the Title page, Copyright information, Table of Contents, and Conference Committee listing.

In these days, the basic performances of white OLEDs are dramatically improved and application of OLEDs to "Lighting" is expected to be true in the near future. We have developed various technologies for OLED lighting with the aid of the Japanese governmental project, "High-efficiency lighting based on the organic light-emitting mechanism." In this project, a white OLED with high efficiency (37 lm/W) and high quality emission characteristics (CRI of 95 with a small variation of chromaticity in different directions and chromaticity just on the black-body radiation curve) applicable to "Lighting" was realized by a two-unit structure with a fluorescent deep blue emissive unit and a phosphorescent green and red emissive unit. Half-decay lifetime of this white OLED at 1,000 cd/m² was over 40,000 h. A heat radiative, thin encapsulation structure (less than 1 mm) realized a very stable emission at high luminance of over 3,000 cd/m². A new deposition source with a hot-wall and a rate controllable valve was developed. Thickness uniformity within +/- 3% at high deposition rate of over 8 nm/s, high material utilization of over 70 %, and repeatable deposition rate controllability were confirmed.

We investigate high finesse organic planar microcavities under different optical pumping conditions. The design of the cavities is chosen to realize the smallest possible cavity thickness of λ/2. We use different coherent light sources to pump the structures optically. 120 fs pulses out of an amplifier system and pulses of 1 ns length from a 532 nm solid state laser are applied. Emission properties of an organic microcavity are further investigated when incoherent light, emitted from an inorganic light emitting diode, is used to excite the cavity layer. A monolithically integrated device is realized, where a high quality organic microcavity is deposited directly onto the surface of a light emitting diode. A set of modified rate equations is applied to simulate input-output curves of different organic microcavities under different optical pumping conditions. In addition to the modified spontaneous emission rates due to the resonator, which are described by the standard set of rate equations, our model takes the finite number of the molecules per mode into account. This limits the upper bound for the number of photons emitted into the mode since absorption saturation takes place during the pumping process by short optical pulses. An analysis of the experimental results show that this effect can substantially modify the lasing characteristics of lambda-half organic microcavities.

We investigate a planar organic microcavity under spatially periodic optical excitation. The host:guest system of Alq3:DCM is the emitting layer embedded in between two dielectric mirrors. Excitation by an interference field of two femtosecond laser pulses generates an array of lasers spaced by few microns. The far field of the cavity response shows conventional stimulated emission at k=0 and, in addition, two stripes of laser emission at oblique angles. The excitation pattern generates a periodic modification of the optical properties of the cavity, a dynamic diffraction grating with a period of few microns. This enhances the spontaneous emission in the direction of the Bragg angle, which depends on the distance of the interference stripes. Via the angle of incidence of the excitation beams, we can optically tune output angle and the wavelength of lasing. Measurements are confirmed by simulations of the mode dynamics inside a lossy cavity with small excitation spot sizes, where the local gain exceeds the total mirror and absorptive losses. We find that adjacent cavity quasimodes couple out of phase at certain separation distances, which critically depend on the quasimode radius and, thus, on the residual absorption. Thus, we gain insight into the development of coherence and mode-locking in microcavities.

We present a theoretical and experimental analysis of operation and degradation of model fluorescent blue bilayer polymer organic light emitting diodes (P-OLED). Optical and electrical simulations of bilayer P-OLEDs are used to highlight the key material and device parameters required for efficient recombination and outcoupling of excitons. Mobility data for a model interlayer material poly (9,9-dioctylfluorene-N-(4-(2-butyl)phenyl)-diphenylamine) (TFB) and a model fluorescent blue light emitting material poly-(9,9'- dioctylfluorene-co-bis-N, N'-(4-butylphenyl)-bis-N,N'- phenyl-1,4-phenylenediamine) (95:5 mol%) (F8-PFB random copoloymer), is shown to satisfy the key charge transport characteristics required to ensure exciton formation at the optimum location for efficient extraction of the light where μ_h (LEP) < μ_e (iL) < μ_e (LEP) < μ_h (iL). A method to measure the photon generation zone profile and dipole orientation is presented and shown to follow the expected behavior. The efficiency drop of P-OLEDs during device operation is a known issue, the understanding and prevention of which is key for the commercial success of P-OLED technology. We present a detailed degradation study of devices containing model materials, and highlight the generation of fluorescence quenching sites as the key factor limiting the operational stability. A striking feature of this degradation is its partial (~50%) reversibility upon baking above the LEP glass transition temperature. Some reversibility is also observed in the conductivity, suggesting a common origin to the optical and electrical degradation. We also show that the species responsible for the generation of the reversible PL quenching sites are the excitons themselves, and that optically excited excitons can also generate many of the features characteristic of electrical stressing. Finally we demonstrate that materials with a dramatically improved lifetime also suffer from a similar, although slowed down, degradation mechanism, where the reversible component is increased to almost all (>90%) of the quenching sites produced. This highlights the importance of understanding these reversible phenomena in improving P-OLED lifetime and commercial adoption of the technology.

The orientation of the emissive dipole moments in organic light-emitting diodes (OLEDs) has a major impact on the optical outcoupling efficiency and, consequently, on the device performance as well as on possible optimization strategies. In this contribution we discuss a general method to quantify the amounts of parallel and perpendicular emissive sites in OLEDs. The presented in-situ-method is based on measurements of the far-field emission of an electrically operating device and corresponding optical reverse simulations. For the reverse simulation we take advantage of the fact that perpendicular dipoles only contribute to transverse-magnetic polarized light emission. In general, the method can be applied to all classes of emissive materials for OLEDs, including small-molecule and dendrimer materials. In the present study we utilize bottom emitting polymeric OLEDs with two different stack architectures: (A) a conventional OLED stack optimized for maximum performance and (B) a well adapted OLED stack, where the contribution of perpendicularly oriented dipoles to the radiation pattern in air is optically enhanced. We demonstrate that for OLED (A) perpendicular dipoles are "invisible" in the optical far-field, because almost all light from perpendicularly oriented dipoles is trapped inside the OLED stack. Consequently, no information about the emitter orientation can be gained from the radiation pattern of this device. In contrast, OLED (B) clearly shows that the radiation pattern is generated by 93.5 % parallel and 6.5 % perpendicular dipoles. Assuming a Gaussian distribution of dipole orientations in the particular emissive material, the dipoles stagger around the preferred parallel direction with an 1/e-angle of ± 22°.

In this paper, we introduce an extension of the coupled electronic-optical model to simulate organic light-emitting devices (OLEDs). We couple the influence of the optical environment to the exciton transport equation which yields a position dependent exciton lifetime. Thereby we get a more accurate spatial distribution of excitons, namely the emission profile. We show that the emission profile is dependent on the intrinsic quantum efficiency. In a second part of this paper, an extended numerical algorithm for extraction of the emission profile from emission spectra is presented. The extended extraction algorithm takes the influence of the optical environment into account. We call it the excitonic lifetime fitting method (ELF) and compare it to a conventional linear fitting method. On the basis of consistency checks we demonstrate the influence of noisy emission spectra and device thicknesses. Our investigations show the impact of the ELF method, which improves the accuracy and robustness of the extracted emission profile considerably up to 120 %.

We report on the latest progress in the field of organic p-i-n tandem solar cells. The external quantum efficiencies of a tandem solar cell with two complementary absorbing bulk heterojunctions with an efficiency of 6.07% (certified by Fraunhofer ISE) with an active area of about 2cm² is analyzed. These solar cells are extremely stable: a reduction of only 3% of its initial power conversion efficiency was measured when stored at 85°C for 5000 hours. The solar cell does not show any reduction in efficiency when stored under continuous illumination of a tungsten lamp corresponding to 1.5 suns for 5000 hours. Furthermore, we present the latest results on optimized tandem solar cells showing a power conversion efficiency of 7.66 % (certified by Fraunhofer ISE, active area of 1.1cm²).

Besides efficiency and cost, lifetime is another important factor for the commercialisation of small molecule organic solar cells. To quickly achieve results one has to perform accelerated measurements. Thus, knowledge about accelerating factors is necessary to relate these results with measurements under real working conditions. Here, we compare different conditions for accelerated lifetime measurements of organic solar cells. The investigated p-i-n-devices contain a bulk heterojunction of Zinc-Phthalocyanine (ZnPc) and the fullerene C60 as photoactive materials. Doped layers of a large triarylamine-based amorphous wide gap material (Di-NPB) and C60 are used as hole and electron transport layer, respectively. For all devices, the IV characteristics are recorded during the entire measuring time. Unencapsulated solar cells show a rapid degradation due to the strong impact of atmospheric gases like oxygen or water vapour. Lifetimes (t80) of 43 to 110 hours are observed. Devices illuminated by blue light show a faster degradation than those exposed to red light. Additionally, the degradation is further accelerated when the intensity of blue light is increased. The comparison of external quantum efficiency measurements performed before and after ageing verifies that the used photoactive materials are stable. The intensity has the largest influence on degradation dynamics. Our results for solar cells illuminated by white light LEDs show that at intensities up to 100mW/cm² the power conversion efficiency increases with time. This effect was observed over nearly 2000 hours of operation. An intensity of more than five suns is required to reduce the efficiency of our solar cells with time. This reduction is mainly driven by losses in the Fill Factor and a slight decrease of short circuit current density. Nevertheless, extrapolated lifetimes of up to 5000 hours are still observed.

Typically high efficient OLED device structures are based on a multitude of stacked thin organic layers prepared by thermal evaporation. For lighting applications these efficient device stacks have to be up-scaled to large areas which is clearly challenging in terms of high through-put processing at low-cost. One promising approach to meet cost-efficiency, high through-put and high light output is the combination of solution and evaporation processing. Moreover, the objective is to substitute as many thermally evaporated layers as possible by solution processing without sacrificing the device performance. Hence, starting from the anode side, evaporated layers of an efficient white light emitting OLED stack are stepwise replaced by solution processable polymer and small molecule layers. In doing so different solutionprocessable hole injection layers (= polymer HILs) are integrated into small molecule devices and evaluated with regard to their electro-optical performance as well as to their planarizing properties, meaning the ability to cover ITO spikes, defects and dust particles. Thereby two approaches are followed whereas in case of the "single HIL" approach only one polymer HIL is coated and in case of the "combined HIL" concept the coated polymer HIL is combined with a thin evaporated HIL. These HIL architectures are studied in unipolar as well as bipolar devices. As a result the combined HIL approach facilitates a better control over the hole current, an improved device stability as well as an improved current and power efficiency compared to a single HIL as well as pure small molecule based OLED stacks. Furthermore, emitting layers based on guest/host small molecules are fabricated from solution and integrated into a white hybrid stack (WHS). Up to three evaporated layers were successfully replaced by solution-processing showing comparable white light emission spectra like an evaporated small molecule reference stack and lifetime values of several 100 h.

We report on monochrome top emitting organic light emitting diodes (OLEDs) with inverted layer structure and discuss the optical and electrical optimization of OLED devices comprising the orange phosphorescent emitter Ir(MDQ)₂(acac). We show that first, charge balance within the emitting layer is an important factor for efficient generation of light and second, optical outcoupling is a critical issue in top-emitting devices. We demonstrate the use of doped charge transport layers for efficient injection of charge carriers and optical modeling to improve outcoupling. The latter one is done via optimized cavity tuning and application of a dielectric capping layer. Finally, driving voltages of 4.2V at 1000 cd/m², 19 lm/W and 17% external quantum efficiency (EQE) from devices made on metal substrates are reached.

Charge transport in disordered organic blends is studied theoretically by numerically solving the Pauli master equation. The influence of temperature, electric field, and charge carrier concentration on blend mobility are assessed. Important differences between neat materials and blends are found: The dependence of mobility on charge carrier concentration is more pronounced in blends and it is influenced by the electric field strength. At low charge carrier densities, blend mobility is found to decrease with increasing field.

Accurate mobility determination is essential to model and improve the efficiency of organic solar cells. A frequently used method to determine charge carrier mobilities is called CELIV(charge extraction by a linearly increasing voltage). In this technique a voltage ramp is applied to the device in order to extract the free charge carriers inside the cell. With an extended method called photo-CELIV the free charge carriers are first generated by a short laser pulse and are then extracted after an adjustable time. To analyse the experiment analytical formulas are used. We simulate the CELIV and photo-CELIV method with a fully coupled electro-optical model. Our numerical model allows us to reveal the limitations of analytical expressions used to analyse CELIV transients. The influence of the mobility, the series resistance, the voltage slope and the illumination intensity on the CELIV transients are studied. We show that using the analytical formulas only the order of magnitude of the mobility can be determined. We also perform CELIV measurements on organic bulk heterojunction solar cells based on a PT5DPP:PCBMC70 blend. By fitting the numerical simulation to the measured transients we extract charge carrier mobilities, the recombination efficiency and the series resistance.

Semiconducting single wall carbon nanotubes (s-SWNT) are unique monodimensional material of particular interest in photonics for their direct band-gap, allowing tunable near-IR luminescence from electron-hole recombinaison. However, the presence of metallic nanotubes and impurities in real carbon nanotubes samples creates several non radiative relaxation mechanisms, leading to an effective quenching of s-SWNT photoluminescence and limiting their usability in photonics devices. Recently, we have developed a process to selectively extract s-SWNT and embedded them in polyfluorene (PFO) thin films. A removal of metallic nanotubes leads to an enhancement of the photoluminescence properties, with a 6-fold increase of the photoluminescence intensity of (8,6) s-SWNT. Development of nanotubes based photonics devices is also reported. The SWNT-based layer was inserted between two Bragg mirrors to form a Fabry-Perot cavity, leading to a huge photoluminescence enhancement by a factor of 30 in comparison with an identical film and by a factor of 180 in comparison with a non s-SWNT enriched film.

We present a combined quantum-chemical and Monte Carlo approach for calculating exciton transport properties in disordered organic materials starting from the molecular scale. We show that traps and energetic disorder are the main limitations for exciton diffusion in conjugated polymers. An analytical model for exciton hopping in a medium of sites with uncorellated energetic disorder gives a quantitative description on the dependence of the diffusion length to both the energetic disorder strength and temperature. We demonstrate how traps and energetic disorder can pin down the diffusion length in conjugated polymers to values below 10 nm.

Charge mobility is a key parameter for understanding the performance of organic semiconductor devices and materials. A range of techniques is available that can measure charge mobility with varying accuracy and precision. We review the dark injection transient current method from a metrology perspective with a particular emphasis on quantification of uncertainties that arise from the technique itself and from the inherent variability of devices and materials. We have carried out a systematic study of the space-charge-limited dark injection transient current technique as a method of measuring charge mobility in polymer organic light emitting diodes, paying particular attention to varying the amplitude, duration and repetition rate of the applied voltage and to environmental factors such as changes in the ambient temperature. We show that the results of the experiment depend strongly on the previous history of the device and that both long-term and short-term effects can be identified. As a result, we are able to quantify the contribution of these effects to the uncertainties associated with estimates of charge mobility obtained using the dark injection method.

Corresponding to their relative low work function, Ca and Mg are interesting metals for cathodes in organic light emitting devices. In this study, the interaction of these metals with the blue phosphorescent emitter material Ir(cnpmbic)₃ is investigated by in-situ infrared spectroscopy. Thin films of the organic material are deposited by vapour sublimation under ultra-high vacuum conditions. Further deposition of Ca on the organic layer at room temperature gives rise to new features in the infrared spectrum of the sample. The new features indicate diffusion of Ca into the organic layer and do not appear at much lower temperature (110 K). They are attributed to dynamic charge transfer processes that may occur at rough metal surfaces. On the other hand, Mg deposited at room temperature does not stick on the organic material.

The fabrication and characterization of highly efficient and photostable second-order distributed feedback lasers (DFB), based on polystyrene films doped with a perylenediimide (PDI) derivative as active laser material, is reported. DFB gratings were obtained via thermal nanoimprint lithography and transferred to SiO₂ substrates by reactive ion etching. The influence of the PDI concentration on the laser performance has been investigated. The best results were obtained for the device based on the 0.5 wt% PDI-doped film, that emits at a wavelength of 571 nm, with a threshold of 2.5 μJ/pulse and a photostability halflife of around 500 min; i.e. 300000 pump pulses. The effectiveness of the DFB grating is evidenced by the decrease in threshold in two orders of magnitude with respect to the amplified spontaneous emission threshold obtained for a similar film deposited over a SiO₂ substrate without grating.

Holographic surface relief gratings written in azobenzene containing films were studied for the use as masters for polymeric thin film distributed feedback (DFB) lasers. Light induced mass transport driven by E-Z isomerization in azobenzene containing materials have shown to be attractive for all optical and one-step fabrication of periodic surface structures with varying parameters for different optical applications. Based on new azobenzene materials and their holographic processing deep surface relief gratings were generated with grating pitches in the range of 400 nm as resonant structures for second order DFB lasers emitting in the VIS range. Nanoimprint techniques enabled multiple duplications of azobenzene master gratings in UV adhesives. The replicas were coated via spin casting with thin films of red light emitting polymer layers to form DFB thin film lasers. These active layers are guest-host-systems consisting of an UV-light absorbing conjugated polymer as host transferring its excitation via Förster resonant energy transfer to a red emitting conjugated polymer. Simple adjustment of grating depth via controlling of illumination time allowed it to investigate the influence of the corrugation depth and thereby the coupling of laser light and grating on the lasing behavior of second order DFB lasers in the red region. For this purpose multiple surface structures with different corrugation depths of up to 130 nm were generated holographically, duplicated and coated.

We report on the fabrication of large-scale surface gratings by laser interference lithography and reactive ion etching on which we evaporated a thin film of the organic semiconductor tris(8-hydroxyquinoline) aluminum doped with the laser dye 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyril)-4H-pyrane. We created a thickness gradient by using a rotating shadow mask evaporation technique. This allowed us to continuously tune the emission wavelength from 606 nm to 661 nm on a single substrate. After encapsulation, we demonstrated the usefulness of such low-cost and tunable organic semiconductor lasers by conducting simple fluorescence excitation and transmission spectroscopy measurements using a minimal amount of additional optical components.

The power conversion efficiency of a polysilicon solar cell is nearly 20%, while that of an amorphous silicon solar cell exceeds 15%. However, as silicon material is inorganic, the simple fabrication of a flexible, lightweight and inexpensive inorganic solar cell is difficult. These limitations of inorganic materials have fuelled active study and considerable progress in the domain of organic thin film solar cells on a global scale. After a bulk-hetero junction structure was introduced in an organic thin film solar cell, one of the latter with power conversion efficiency exceeding 6% was reported. In this study, ethanol, a weak solvent, was added to the 0.01w%P3HT, the 0.01w%PCBM, and the mixed solution of the 0.01wt%P3HT respectively, all of which were dissolved in chloroform. From thin films fabricated by these solutions, P3HT grains and PCBM aggregations are observed with, and evaluated by AFM images and UV-vis spectra.

As organic thin film solar cells fabricated by the active layer of organic materials are economical, lightweight, and flexible, as well as generating no CO₂, and being easy to fabricate, they have attracted significant attention as green energy sources from a past decade to date. Therefore, their power conversion efficiency (PCE) has been investigated and studied worldwide. In organic thinfilm solar cells, the effect of the performance depends not only on the adopted active material but also relates to the molecular orientation on the electrode. Using a mixed solution of Poly(3-hexylthiophene) and PCBM, both of which were dissolved in a solvent, the organic thin films were fabricated using the paint and spray methods, while the morphology of the thin film was evaluated by an AFM image, UV/vis spectra, and so forth. Based on these data, an organic thin-film solar cell using both solution methods for the active layer was fabricated, and the performance evaluated and examined. For organic thin film solar cells fabricated using a spin-coating method, the open-circuit voltage (Voc) is 0.41V, the short circuit current density (Jsc) is 2.07mA/cm², and the fill factor is 0.34, while the efficiency η of PCE become 0.29%. In the spray method, the short circuit current (Isc) is 2.5 mA/cm², the open circuit voltage (Voc) is 0.45 V, the fill factor (FF) is 0.28, and the power conversion factor (PCE) 0.35%. The area of organic solar cells fabricated by spin coating and spray methods is 1 cm² respectively. The organic solar cells are not thermally treated, and hence have high respective power conversion efficiencies.

Organic solar cells have been attracting attention due to their economic and lightweight nature that facilitates processing. However, they also have low power conversion efficiency and short lifespans. Therefore, with practical organic solar cells in mind, solving these problems is important. To improve the power conversion efficiency of organic solar cells, the organic solar cell performance of poly(3-hexylthiophene-2,5-diyl)(P3HT)/PCBM thin film using poly(3-ocxylthiophene) was studied with the bulk heterojunction structure. It was shown that a red shift occurred by adding P3OT to the P3HT/PCBM mixture film at the absorption wavelength area of the active layer. This indicates that the formation of the P3HT grain and the aggregate of the PCBM molecule occur because of the P3OT addition. In the heat-treatment sample, it also emerges that the heat-treatment has an effect similar to the P3OT addition because it causes red shifts in both the P3HT/PCBM and P3OT/P3HT/PCBM thin films. This indicates that the formation of the P3HT grain and the aggregate of the PCBM molecule occur because of the P3OT addition. In the heat-treatment sample, the heat-treatment is understood to have an effect similar to the P3OT addition because it causes red shifts in both the P3HT/PCBM and P3OT/P3HT/PCBM thin film. Under preparatory conditions without thermal or solvent annealing, the power conversion efficiency, short circuit current, and open voltage and fill factor are 0.6%, Isc=3mA/cm², Voc=0.7V and 0.28, respectively.

For diode device structures, the vertical transport of charge carriers across the device is expected to dominate its' performance. In planar organic molecules, where the π-stacking direction is normal to the main body of the molecule, charge transport is highly anisotropic and related to the orientation of the molecules relative to the substrate. On ITO, we have confirmed with AFM and X-ray scattering (reflectivity and grazing incidence X-ray diffraction ) that PTCDI-C₈, an electron accepting photoactive molecule, forms large crystalline domains consisting of tilted, up-right standing molecules. Similarly to that observed on SiO₂ substrates, the domain size can be tuned by adjusting the substrate temperature during growth. In such a configuration, the charge transport is dominated by carrier movement parallel to the substrate, along the π-stacking direction, with vertical transport limited by hopping between layers. We observed that in diodes using such films, the developed charge density increased with the lateral island size. In the vertical direction, charge transport is best described by a thermally activated hopping mechanism. This type of behaviour can have significant implications for nanostructured bulk heterojunctions of such films, when combined with electron donors such as pentacene or diindenoperylene, to be used in small molecule solar cells.

Most commercially available photovoltaic solar cells are crystalline silicon cells. However, in indoor environments, the efficiency of silicon solar cells is poor. Typically, the light intensity under artificial lighting conditions is less than 10 W/m² as compared to 100-1000 W/m² under outdoor conditions. Moreover, the spectrum is different from the outdoor solar spectrum and there is more diffuse than direct light. Taken into account the predicted cheaper costs for the production of organic solar cells, a possible niche market for organic PV can be indoor applications. In this article, we study the influence of the narrow absorption window, characteristic for organic solar cells, for different indoor conditions. This comparison is made for typical artificial light sources, i.e. a common incandescent lamp, an LED lamp and a "warm" and a "cool" fluorescent tube, which are compared to the outdoor AM 1.5 spectrum as reference. The comparisons are done by simulation based on the quantum efficiencies of the solar cells and the light spectra of the different light sources. A classical silicon solar cell is used as reference. In this way we determine the appropriateness for indoor use of organic solar cells.

We present a spectroscopic study of the photoinduced excited-state processes in new materials for polymer solar cells and organic-light emitting diodes, which are based on extended conjugated terpyridine systems. Various spectroscopic tools were combined to investigate the photoinduced dynamics in such systems from the Franck-Condon point up to nanoseconds after light-absorption. The intriguing finding of dual luminescence from a novel class of terpyridine complexes are discussed.

We investigate the influence of particle plasmon resonance of Au nanoislands structures on the exciplex emission in the polymer blend of poly (9, 9'-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly (9,9'-dioctylfluorene-co-bis-N,N'- (4-butylphenyl)-bis-N,N'-phenyl-l,4-phenylenediamine) (PFB). The experimental results indicate that when the particle plasmon resonance of the gold nanoisland structures overlaps the spectral range of the exciplex emission, significant enhancement of the photoluminescence can be observed. Furthermore, longer lifetime has been measured for the red-shift emission of the exciplex. We proposed that the localized field due to the particle plasmon resonance of the Au nanoislands has modulated the mechanisms for the formation of exciplex, which may be related to the exciton diffusion, charge transfer, and phase separation at the interface between the two materials.

Photochromic polymer composites were fabricated by encapsulating dye solution in a polycarbonate membrane. The membrane contained through holes of 50 nm diameter. These nanoholes provided a sufficient free volume for the dye molecules to change their structure in the photochromic isomerization process. A polymer composite containing a toluene solution of diarylethene exhibited red color when it was irradiated with violet laser, and returned to the transparent state by green laser irradiation. Another polymer composite containing spiropyran turned to blue by ultraviolet lamp irradiation and returned to the transparent state by green laser irradiation. A nonlinear input-output characteristic and a rewritable-grating function were demonstrated by using these photochromic polymers.

The photopolymers with a hydrophilic matrix as poly(vinyl alcohol), PVA, are versatile holographic recording materials in hologram recording experiments. They use water as solvent and they can be made in layers with several thickness. One of the photopolymers more used is composed of acrylamide as polymerizable monomer, PVA and water as binder. The pair: triethanolamine, TEA, and the dye yellowish eosin, YE, is widely used as initiator system due to its high sensitivity and efficiency. TEA is the radical initiator more used with dyes derived from fluorescein as YE because they can generate a radical by redox reaction under dye excitation by light. The dye is bleached in this process because is decomposed in the photoinitiation reaction. The ethylenediaminetetraacetic acid EDTA has a molecular structure very similar to TEA and therefore could replace it in this kind of photopolymers. The 4,4' azo-bis-(4-cyanopentanoic acid), ACPA, is a radical initiator that is soluble in water and usually used in polymerizations in solution with thermal initiation. In this work, we use EDTA and ACPA in order to check their properties as radical initiator in the photochemical reaction that takes place inside the photopolymer while a hologram is being recorded. We will compare the results obtained with those derived from TEA and will evaluate the possibilities for these substances.

We present a procedure for the modeling of the dispersion of the nonlinear optical response of complex molecular structures that is based strictly on the results from experimental characterization. We show how under some general conditions, the use of the Thomas-Kuhn sum-rules leads to a successful modeling of the nonlinear response of complex molecular structures.

This paper presents latest own results in the development of reversible photochromic and irreversible photofluorescent polymer systems providing fabrication of multilayer recording media for 3D optical memory with super high information capacity. It was shown that synthesized thermal irreversible photochromic diarylethenes into plastic binders allow to prepare photochromic polymer layers providing nondestructive refractive read-out of optical information. These photochromic polymer layers were used for preparation of six-layer recording media tested with the positive results using the framed optical device. This device imitated layer-by-layer writing, erasure and read-out of optical signals. Experimental evidences for making photochromic polymer layers based on a mixture of photochromic diarylethene and dye - phosphor with nondestructive fluorescent read-out are presented too. Polymer systems based on light-sensitive chromones manifest an irreversible photochemical transformations of these non-fluorescing compounds into the fluorescent products under UV irradiation. Received results open perspectives for making multilayer optical discs for bitwise working (based on photochromic systems) and archival (based on irreversible photofluorescent systems) optical memory with information capacity more 1 TB.

We report on the measurement of the multi-photon absorption dispersion of polydiacetylene-decorated silver nanoparticles in water solution. They were prepared by self assembly of the monomer 10,12-pentacosadiynoic acid (PCDA) onto pre-formed chitosan-stabilized Ag nanoparticles (Chit-AgNps) followed by photopolymerization of the diacetylenic outer shell. Z-Scan technique with fs pulses in open aperture configuration was employed: the spectral range covered the region between 1150 and 1350 nm. We tentatively attribute our results to a two photon state (2A_g) which peaks at 600 nm. This result is consistent with the fluorescence spectrum that shows an emitting state lying at about 650 nm, in addition to a peak at 568 nm which is attributed to the emission of an orange form of the polymer. However we cannot rule out the possibility that we are also dealing with higher order absorption processes and further studies are needed to clarify this point and to provide a deeper insight into the origin of the emission spectrum.

The molecular linear and second-order nonlinear optical (NLO) properties of a series of donor (D)-π-acceptor (A) merocyanine molecules have been studied in three solvents, dimethylformamide (DMF), tetrahydrofuran (THF), and chloroform (CHCl₃). All the compounds have a cyanodicyanomethylidenedihydrofuran electron acceptor system with either a pyridinylidene or quinolinylidene donor group. In high polarity solvents the molecules with a quinolinylidene donor have larger first hyperpolarizabilities than those with a pyridinylidene donor, while the opposite is true in low polarity solvents. The molecules under investigation have an aromatizable donor unit, which leads to a high degree of charge separation in the ground-state; as a result they have a strong tendency to aggregate. To minimize these interactions arene-rich bulky groups have been introduced in a number of these compounds.

We demonstrate volume holographic recording in nanoparticle-polymer composites using thiol-ene monomers capable of step-growth polymerization by which shrinkage can be reduced as low as 0.2%. The reduced shrinkage is comparable to other low-shrinkage dry photopolymer systems such as those including a high content of inert binder components and using monomers capable of cationic ring-opening polymerization. It is shown that the thiol-ene based organic nanoparticle-polymer composites possess the refractive index modulation and the material sensitivity of 8×10^-3 and 1014 cm/J, respectively, in the green, larger than the minimum acceptable values of 0.005 and 500 cm/J for holographic data storage.

We describe an experimental investigation of the nonlinear optical properties of nanocomposites incorporating organic (hyperbranched polymer)-metallic (Au or Pt) nanoparticle complex embedded in polymer films. Zscan techniques are employed to measure the effective third-order nonlinear optical susceptibilities χ(3) eff of the composites with 35 ps pulses at 532 nm. The relative sign of the real and imaginary parts of χ(3) eff could be explained qualitatively by the Kramers-Kronig relation. The third-order nonlinear optical susceptibilities of Au and Pt nanoparticles from the measured values for χ(3) eff were also determined to be (-5.48 + 4.76i)×10^-8 and (4.43 - 0.65i)×10^-6 esu, respectively, at 532 nm.