Photorefractive Applications Research Articles

Orientation dependence of polarization-modulated photovoltaic effect of relaxor-based Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals

Noncentrosymmetry ferroelectric materials coupled with switchable polarization are promising candidates for photovoltaic applications because of their unique dissociation mechanism of photogenerated excitons associated with bulk polarization. Here, we study the photovoltaic properties of relaxor-based 24Pb(In1/2Nb1/2)O3–47Pb(Mg1/3Nb2/3)O3–29PbTiO3 (24PIN–47PMN–29PT) single crystals with a large remnant polarization and a proper optical bandgap along various crystallographic orientations. The 24PIN–47PMN–29PT single crystals are found to exhibit a modulated photovoltaic response by switching the poling direction, while their current–voltage curves present a linear relation. The superior photovoltaic response in the [111]C‐oriented crystal suggests that the photovoltage is strongly dependent on the crystallographic direction because of the polarization intensity difference. In addition, the domain configuration, phase structure, ferroelectric performance, and optical characteristics of 24PIN–47PMN–29PT single crystals are investigated, providing clues to the origin of the anomalous photovoltaic effect of these single crystals. Our results indicate that the photovoltaic performance of 24PIN–47PMN–29PT single crystals can expand their potential applications in photovoltaic devices, photorefraction, and photorefractive optical applications.

Effects of transition metal dopants on the electronic structure of potassium niobate

Potassium niobate (KNbO3) is an important ferroelectric and photorefractive material that finds multiple nonlinear optical and photorefractive applications such as two-beam coupling and dynamic holography. We employ standard Density Functional Theory to examine two defect complexes in KNbO3 doped with 3-d transition metals. These defect complexes involve the substitution of a Nb with a 3-d transition metal element and (1) a coordinating oxygen vacancy induced in the nearest-neighbor oxygen shell or (2) a non-coordinating oxygen vacancy induced in the supercell as far away as possible from substitution impurity. With the exception of Ti and V, the 3-d transition metal dopants studied here may represent viable dopants for purposes of extending the photorefractive spectral response of KNbO3. Our results indicate that each of these complexes introduces defect states into the gap of KNbO3. Furthermore, we notice that the distribution of impurity states changes quite systematically across the 3-d transition metal row, and we note the effects of the disruption of the crystal field in the case of the coordinating O vacancy on the position and ordering of defect states within the gap. Substituting KNbO3 with transition metal ions can, therefore, significantly affect its optical and infrared properties, exemplifying how a detailed understanding of the electronic structure can be an important tool in tailoring the properties of this material for ferroelectric and photorefractive applications.

Streptomerocyanine dyes

Abstract Dyes synthesized by condensation of e. g. 4-N,N-dialkylaminobenzaldehydes, 5-N,N-dialkylamino-2-thiophenaldehydes or 5-N,N-dialkylamino-2-furaldehydes, with open chain active methylene compounds have been given the labels merocyanine, neutrocyanine, methine or styryl dyes. All these classifications are misnomers. In terms of systematic nomenclature, their proper classification is as streptomerocyanine dyes. They are used in textile coloration and in dye diffusion thermal transfer printing (D2T2). Furthermore, they have been investigated for their potential as sensitizer dyes in dye sensitized solar cells (DSSC) and for photorefractive applications.

A calix[4]resorcinarene-based hyper-structured molecule bearing disperse red 1 as the chromophore with enhanced photorefractive performance under non-electric field

A hyper-structured molecule (HSM) CRA-DR1 and a model molecule Ph-DR1 for photorefractive (PR) application under non-electric field were designed and synthesized via highly reactive “click” reaction between alkynyl derivatives of calix [4]resorcinarene (CRA) or resorcinol and an azide derivative of disperse red 1 (DR1) in satisfactory yields. XRD pattern and UV–Vis absorption spectra indicated that the CRA-DR1 with three-dimensional (3D) CRA core could effectively decrease the aggregation, packing and crystallization of the nonlinear optical (NLO) chromophores. AFM images showed a smooth and pinhole-free morphology of the CRA-DR1 film. Two-beam coupling (TBC) experiment was used to test the photorefractive performance in optically transparent films of Ph-DR1 and CRA-DR1 doped with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as a photosensitizer and N-ethyl-carbazole (ECz) as a plasticizer. Without poling and without external electric filed, the coupling gain coefficient obtained in the CRA-DR1-based composite is 147.4 cm−1, which is higher than that of Ph-DR1-based composite (132.6 cm−1) owing to its asymmetrical 3D CRA core. Coupled with its convenient synthesis and commercial DR1, CRA-DR1 could serve as a good candidate for PR application.

Study on the photoconductive properties of charge carriers in donor-acceptor copolymer P(EDOT-FL) and P(EDOT-FL):PCBM blend

The photoinduced charge transfer properties of low band gap donor-acceptor π-conjugated copolymer poly(2,5-(3,4-ethylenedioxythiophene)-alt-2,7-(9,9-dioctylfluorene)) labelled as P(EDOT-FL) has been investigated through solvatochromic and photoconductivity studies. The effect of strong acceptor, Phenyl-C61-butyric acid methyl ester (PCBM) on the photogeneration of free carriers is studied by comparing the fluorescence spectra and photoconductive properties of the polymer-PCBM blend [P(EDOT-FL):PCBM] films with the pristine polymer films. The positive solvatochromism exhibited by the P(EDOT-FL) revealed its photoinduced charge transfer nature of the absorption and emission bands. The blend films exhibited quenching of the fluorescence intensity and showed increased photoconductivity. Internal photocurrent efficiency and photoconductive sensitivity of the pristine P(EDOT-FL) films and P(EDOT-FL):PCBM blend films were calculated as a function of electric field, by measuring the photocurrent generated in the sample. Blend films exhibited higher internal photocurrent efficiency of 86% and photoconductive sensitivity of 5.44×10−7 SW−1cm at 70V/μm. The obtained photoconductive sensitivity at low electric field (<10V/μm) is sufficient for photorefractive applications.

Photorefractive Photonics 2017

PrefaceThis volume of Journal of Physics: Conference Series represents a selection of the contributions presented in the Photorefractive Photonics 2017 (PR17) conference which was held in Qingdao, Shandong, China from July 17 through July 20, 2017. The conference is the successor of the traditional Photorefractive (PR) Conference Series: the International Conference on Photorefractive Effects, Materials and Devices. The first PR Conference was held in Los Angeles, California, USA in 1987. After that, the PR Conference was held every two years around the world: Aussois, France (1989), Beverly, Massachusetts, USA (1991), Kiev, Ukraine (1993), Aspen Lodge, Colorado, USA (1995), Chiba, Japan (1997), Elsinore, Denmark (1999), Delevan, Wisconsin, USA (2001), Nice, France (2003), Sanya, Hainan, China (2005), Olympic Valley, California, USA (2007), Bad Honnef, Germany (2009), Ensenada, Mexico (2011), Winchester, UK (2013) and Villars, Switzerland (2015). The Conference was renamed to be Photorefractive Photonics Conference in 2015. The PR17 conference was organized by Nankai University, Qingdao University and Qingdao Society of Physics.The scientific topics of the PR17 conference include, but not limited to, wave mixing and its applications (T1), nonlinear light-matter interaction and its applications (T2), material engineering and photonic micro-structures (T3), photorefractive lattice photonics (T4), digital photorefractive photonics (T5), and novel photorefractive effects, materials and applications (T6). Note that both traditional topics such as photorefractive wave mixing and new topics such as energy photonics and nano/micro-structures based on photorefractive effects and materials are included, especially, basic issues such as the influence of pyroelectric effect on the photorefractive wave-mixing are considered, and much attention was paid to the development of new applications of photorefractive effects and materials, which reflect the current state of the art of photorefractive research.We would like to thank all scientific topic chairs for their suggestions of invited talks, Prof. Fang Bo for his patience to communicate with the conference attendees, and Dr. Feng Xia for his technical support during the conference preparation. We are also very indebted to the international scientific committees, the conference scientific topic chairs and the local organizing committee for the success of this conference and the quality of this volume.This PR17 conference is financially supported by the National Natural Science Foundation of China, Nankai University and Qingdao University.EditorsGuoquan Zhang, Nankai UniversityWeijin Kong, Qingdao UniversityJingjun Xu, Nankai University

Photorefractive Effect in Plasmonic Waveguides

In this paper, for the first time, the photorefractive effect in plasmonic waveguides is theoretically modeled and investigated in detail. A metal- LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -metal nanostructure is considered, with the LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> being doped with donor and acceptor impurities. The interaction between symmetric and antisymmetric interfering SPP modes is studied. It is shown that a strong symmetric mode can be coupled to a week antisymmetric mode by the mean of photorefractive effect. When the modal losses are taken into account, it was found that losses can limit the interaction length. However, by choosing the proper waveguide length, doping concentration, and amplitude inputs, the photorefractive coupling process is shown yet to be viable despite losses. The coupling effect can be conducted either as an amplification or mode conversion process, promising novel future application. For instant, several known photorefractive applications in microphotonics can be borrowed and implemented in the plasmonic field.

Synthesis and characterization of polytriphenylamine based graft polymers for photorefractive application

Novel graft copolymers, PTPA-g-PEAs containing poly(triphenylamine) (PTPA) backbone and poly(ethyl acrylate) (PEA) branches were synthesized by the oxidative coupling polymerization of triarylamine monomers followed by grafting of ethyl acrylate via an atom transfer radical polymerization (ATRP). Photorefractive (PR) composites based on the graft copolymers showed good static PR properties and fast response time under moderate conditions. The highest diffraction efficiency (19.7% at 45 V/μm) was observed with the composite containing the graft polymer with 18 mol% of graft density and 27 wt% of PTPA. And the fastest response (8 ms at 50 V/μm) was achieved when PTPA content was 68 wt%.

Crystalline perfection, Raman, UV-VIS-NIR and prism coupler investigations on Cz-grown pure and Zn-doped LiNbO3 single crystals

Pure and Zn-doped (1 mol%) LiNbO3 single crystals have been grown by the Czochralski technique. From powder X-ray diffraction analysis, the crystal structure and the lattice strains have been evaluated. The crystalline perfection analysis by high resolution X-ray diffraction revealed that the pure crystal is free from structural grain boundaries and contains predominantly vacancy defects whereas the doped crystal contains low angle structural grain boundaries. The Raman spectral studies indicate no variation in lattice vibrations with slight changes in the peak width and intensity. The Zn doping in crystals leads to an enhancement in optical transparency over the entire visible and near-infrared wavelength range and optical band gap. The prism coupler, refractive indices and birefringence measurements infer that the doped crystal is suitable for photorefractive applications in the ultraviolet wavelength region. The evaluated Li concentration by Raman and UV, as well as birefringence depicts that the grown crystals are congruent in nature with a slight deviation from stoichiometry.

Synthesis and Characterization of Triarylamine-Based Block Copolymers by Combination of C-N Coupling and ATRP for Photorefractive Applications

Poly(4-butyltriarylamine)s with t-butyldimethylsilyl terminal protecting group (PBTPA-TBS) with various molecular weights were prepared by C-N coupling polymerization. The resulting precursors were postfunctionalized and subse- quently used as macroinitiators for atom transfer radial polymerization (ATRP) of n-butyl acrylate (n-BA) and ethyl acrylate (EA). Both the polymerization processes were controlled and the polymers were characterized by 1H NMR, gel permeation chromatography (GPC) and thermal properties, which confirmed the successful synthesis of all the poly-mers. The microphase separated behaviors of the poly (4-butyltriarylamine)-block-poly (butyl acrylate) (PBTPA-b-PBA) were examined by AFM in the film showing phase separation structures for all the polymers. The photorefractive property of the composite based on PBTPA-b-PBA block copolymer was evaluated by two-beam coupling experiment. A relative high gain coefficient of 42.7 cm?1 was obtained at the electric field of 31 V/?m.

Improved ultraviolet photorefractive properties of vanadium-doped lithium niobate crystals

A series of vanadium-doped lithium niobate (LN:V) crystals has been grown and their photorefractive properties were investigated. For 0.1 mol. % V-doped LiNbO(3), a fast photorefractive response of 160 ms was obtained with a 351 nm laser and a total light intensity of 583 mW/cm(2). The measurements of the x-ray photoelectron spectrum and electron paramagnetic resonance show that V(3+), V(4+), and V(5+) ions exist in these LN:V crystals. V(3+) and V(4+) ions correspond to the 420 and 475 nm absorption peaks, respectively. The fast photorefractive response and high sensitivity indicate that LN:V is a suitable candidate for UV photorefractive applications.

Iron doping of lithium niobate by thermal diffusion from thin film: study of the treatment effect

Thermal diffusion from thin film is one of the most widespread approaches to prepare iron doped regions in lithium niobate with limited size for photorefractive applications. In this work, we investigate the doping process with the aim of determining the best process conditions giving a doped region with the characteristics required for photorefractive applications. Six samples were prepared by changing the atmosphere employed in the diffusion treatment in order to obtain different combination of diffusion profiles and reduction degrees and also to check the effect of employing a wet atmosphere. The compositional, optical, and structural properties are then extensively characterized by combining Secondary ion Mass Spectrometry, UV, visible and IR spectrophotometry, High Resolution X-Rays Diffraction, and Micro-Raman Spectroscopy. Moreover, the sample topography was checked by Atomic Force Microscopy. An analysis of all our data shows that the best results are obtained performing a double step process, i.e. diffusion in oxidizing atmosphere and subsequent reduction at lower temperature in an hydrogen-containing atmosphere.

Structural and compositional characterization of LiNbO 3 crystals implanted with high energy iron ions

Iron ions were implanted with a total fluence of 6 × 10 17 ions/m 2 into lithium niobate crystals by way of a sequential implantation at different energies of 95, 100 and 105 MeV respectively through an energy retarder Fe foil to get a uniform Fe doping of about few microns from the surface. The implanted crystals were then annealed in air in the range 200–400 °C for different durations to promote the crystalline quality that was damaged by implantation. In order to understand the basic phenomena underlying the implantation process, compositional in-depth profiles obtained by the secondary ion mass spectrometry were correlated to the structural properties of the implanted region measured by the high resolution X-ray diffraction depending on the process parameters. The optimised preparation conditions are outlined in order to recover the crystalline quality, essential for integrated photorefractive applications.

Photorefractive waveguides in He^+ implanted pure and Te-doped Sn_2P_2S_6

We have demonstrated for the first time, to the best of our knowledge, photorefractive two-wave mixing in He+ implanted waveguides in one of the most promising materials for infrared photorefractive applications, the ferroelectric semiconductor Sn2P2S6. The high optical nonlinearity is preserved after implantation and at the telecommunication wavelength λ=1.55 μm, a maximal two-wave mixing gain of 2.5 cm−1 has been measured in Te-doped waveguides. In the nominally pure material an increase of the effective number of traps after implantation has been observed, resulting in an increase of the two-beam coupling gain by a factor of almost 2 in the 633-1064 nm spectral range. In 1% Te-doped Sn2P2S6 the effect of ion implantation to the photorefractive response is completely different than in pure materials. While the dominant contribution by holes is not considerably affected, a strong, thermally induced charge compensation is observed in the He+ implanted Te-doped waveguides.

Non-linear optical polymers for photorefractive applications

Photorefractive materials can be used to record and erase holograms many times without the need for chemical processing. This places photorefractive materials at the cutting edge for use in updatable holographic display applications. This feature article reviews the basic principles of polymer photorefractivity and the properties of a newly developed bis-triarylamine side-chain photorefractive polymer sensitive at visible and near-infrared wavelengths. The photorefractive composites developed using this polymer exhibit stable dynamic properties under continuous operation combined with video-rate compatible dynamics, and long shelf lifetimes. Recent improvements in the polymer compositions have led to the development of an updateable holographic 3D display, capable of recording and displaying new images every few minutes.

高分子半導体の合成とナノ構造制御

This article describes the synthesis of hole transporting polymers containing triphenylamine (TPA) unit either in side chain or main chain for electroluminescent devices, and photorefractive applications. Radically polymerized polyacrylate having tetraphenyldiaminobiphenyl (TPD) unit showed higher drift mobility compared with conventional poly(N-vinylcarbozole) (PVK). TPA derivatives were reacted with paraformaldehyde or benzaldehyde in the presence of p-toluenesulfonic acid to yield polymers soluble in common organic solvents. Acid catalyzed Friedel-Crafts reactions between TPA derivatives and divinylbenzene were also applied to prepare the main chain polymers. TPA derivatives were oxidatively coupled to afford polymers with well-defined structure. Resulting polymer sensitized with fullerene showed much higher photoconductivity than PVK. Electron transporting polymers having oxadiazole, fluorene, or thioxanthene unit are also introduced. For the further improvement of device performance, molecular design for multifunctional and multiphased materials including block copolymers and rod-coil type polymers is described.

Synthesis and characterization of novel photoconducting carbazole derivatives in main-chain polymers for photorefractive applications

We have prepared hole-transporting polymers that have carbazole and 3,3′-dicarbazole in the main chain by polycondensation based on Fridel–Craft reaction via cations generated by proton of p-toluene sulfonic acid catalyst. In the device, they display high diffraction efficiency at low external electric field. The DiCz composite had a high diffraction efficiency of 82.4% at 52 V/μm and a photorefractive response time constant of 1.18 s at an electric field of 50 V/μm and a writing intensity of 60 mW/cm 2. The samples have excellent properties with respect to optical quality and shelf-lifetime.

Holographic gratings in photorefractive materials: A review

In this paper, the fundamental characteristics of the photorefractive effect, both in bulk crystals and waveguides, as well as some of the most important photorefractive materials, their properties, and applications, are reviewed. In the last section, we report some experimental considerations on diffracted power from holograms written in pure LiNbO3 and Fe:LiNbO3 crystals and waveguides.

Synthesis of Optically Active Photoresponsive Multifunctional Polymer Containing the Side‐Chain Azocarbazole Chromophore

AbstractSummary: A new optically active photochromic polymethacrylate containing the carbazole moiety, deriving from the chiral monomer (S)‐(4‐cyanophenyl)‐(3‐{9‐[2‐(2‐methacryloyloxypropanoyloxy)ethyl]carbazolyl})diazene [(S)‐MLECA] has been prepared and fully characterized with the aim to obtain a multifunctional derivative possessing at the same time chemical moieties suitable to NLO and optical storage, to chiroptical switches, and to photorefractive and photoconductive applications. Spectroscopic, thermal and chiroptical characterizations clearly indicate the occurrence of dipolar interactions between chromophores and the presence of an ordered chiral conformation of one prevailing helical handedness, at least for chain segments of the macromolecules.Structure of poly[(S)‐MLECA].magnified imageStructure of poly[(S)‐MLECA].

Demonstration of an Fe doped KNbO3 photorefractive hybrid

Highly birefringent liquid crystals are attractive for photorefractive applications but device operation, usually restricted to the Raman-Nath regime, can be degraded by small phase shifts between the optical and refractive index gratings and coarse grating spacings with narrow beam intersection angles. Having to apply external electric fields and tilt the cell at an angle to the grating k vector cause further complications. In this letter, two-beam coupling in a hybrid photorefractive cell comprising a nematic liquid crystal layer influenced by an Fe doped KNbO3 window is described. The KNbO3 window determines photorefractive properties while the liquid crystal amplifies the overall refractive index modulation. Full Bragg matched gain and large beam intersection angles, with perfect 90° phase shifts between the optical and refractive index gratings, at normal incidence, without the need for an external field are demonstrated.