Organic Photorefractive Composites Research Articles

Enhancement of the response time in organic photorefractive composites using alkoxy-substituted PDCST as a nonlinear optical chromophore: publisher's note.

This publisher's note contains corrections to Opt. Lett.45, 6767 (2020)OPLEDP0146-959210.1364/OL.409743.

Enhancement of the response time in organic photorefractive composites using alkoxy-substituted PDCST as a nonlinear optical chromophore.

The ease of the molecular orientation of a chromophore has an important effect on the electro-optical (EO) properties of polymeric photorefractive (PR) composites. A derivative of 4-piperidinobenzylidene-malononitrile (PDCST) with an alkoxy group added as a side branch was synthesized to improve the molecular orientation characteristics. Electrophoresis was performed on the polymeric PR composite to which the improved PDCST had been added. The optical properties and response times were examined to evaluate the effects of the substitution of the alkoxy group. PDCST substituted with the alkoxy group showed enhanced EO properties and a PR grating formation rate.

1064‐nm Sensitive Organic Photorefractive Composites

Organic photorefractive composites with sub-second response time and complete internal diffraction efficiency at low-intensity 1064 nm illumination are presented. Direct sensitization of the composites is provided by the C84 fullerene derivative [84]PCBM or the organic/inorganic hybrid Ni-dithiolene complex TT-2324. Holographic measurements on blends with varying contents of sensitizer are demonstrated.

Tunable color filter with surface plasmon resonance using organic photorefractive composite

We report on a tunable color filter with surface plasmon resonance (SPR), excited by a photorefractive (PR) diffraction grating. When a white light was incident at the diffraction grating formed by a PR effect, the SPR generated at a metal-dielectric material interface was absorbed, and the reflected light showed a complementary color. When the period of the PR diffraction grating was modified by alteration of the optic configuration, the wavelength at which the SPR excitation led to a reflection minimum changed and the spectrum of the reflected light also changed. A well-known equation was used to help us understand the experimental results. All experimental results are in good agreement with the calculation predictions. This result could lead to a new type of tunable color filter.

Tunable color filter with surface plasmon resonance using organic photorefractive composite

Tunable color filter with surface plasmon resonance using organic photorefractive composite

Chromophore Concentration Effect on Photorefractive Performance of Organic Photorefractive Composites

We investigated the effect of chromophore (DB-IP-DC) on the photorefractive performance in organic photorefractive composites. We prepared several photorefractive composites; PSX-Cz:TNF:DB-IP-DC:BBP = 69:1:x:(30 − x) wt% and measured photocurrent and PR grating build-up time. The photocurrent was measured by the competition between the hole trapping and detrapping rates from DB-IP-DC and PSX-Cz. The PR grating build-up rate increased with the increment of photocurrent.

Bipolar charge transport in an organic photorefractive composite

The authors report on tuning the near-infrared holographic recording speed in a poly(N-vinylcarbazole) based photorefractive composite by illuminating it at a wavelength of very strong absorption. Due to the small penetration depth of the light under these conditions this approach allows to flood the material with charge carriers from the side of the sample. Even at light levels much stronger than the write beams, this additional illumination does allow for grating recording. However, under these conditions competition between positive and negative charges leads to sign inversion of the two-beam coupling gain coefficient during recording. An improvement of the recording speed is demonstrated.

Determining the photoelectric parameters of an organic photoconductor by the photoelectromotive-force technique

We report on a theoretical model to describe the non-steady-state photoelectromotive-force (photo-EMF) effect in organic photoconductors. Unlike the conventional theory of the photo-EMF effect developed for crystalline materials, this model accounts for the field dependence of the charge generation quantum efficiency and charge carrier mobility. To verify our findings a detailed experimental study of the charge carrier generation and transport processes in a organic photorefractive composite was performed using the photo-EMF effect and ac photocurrent measurements. The investigated composite was based on a conjugated triphenyldiamine based polymer (TPD-PPV) sensitized with a highly soluble fullerene derivative (PCBM). Our results show that at zero and low dc field the dependence of the photo-EMF signal on frequency, grating period and external electric field is well described by the standard model originally developed for an inorganic monopolar photoconductor with finite charge carrier lifetime. In this regime the photo-EMF effect was used to determine zero- and low-field photoelectric material parameters including the low-field hole mobility $({\ensuremath{\mu}}_{0,h}=1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{V}\phantom{\rule{0.2em}{0ex}}\mathrm{s})$, the effective charge carrier lifetime $(\ensuremath{\tau}=45\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s})$, the diffusion length $({L}_{D}=114\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$, and the primary charge carrier generation efficiency $(\ensuremath{\Phi}=5.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}%)$. In addition, the validity of the Einstein relation $(D∕\ensuremath{\mu}=25\phantom{\rule{0.3em}{0ex}}\mathrm{meV})$ was verified for the low-field regime. At high electric fields the signal behavior deviates significantly from the trend predicted by the standard model for inorganic photoconductors. This behavior which is mainly attributed to the strong field dependence of the charge generation rate is well described by our model.

Effect of field-dependent photogeneration on holographic contrast in photorefractive polymers

The field-dependence of the charge photogeneration efficiency reduces the holographic contrast in an organic photorefractive composite. In this article, the Braun model for field-dependent photogeneration efficiency is incorporated into the standard model of photorefractivity. Using this formalism, the effect on the space-charge field, and thereby holographic index contrast, is calculated directly without the need for empirically found parameters. The dependence of the space-charge field on experimental geometry is also analyzed. A powerful description of the effective space-charge field is thus derived and is experimentally verified. This analysis is then used to compare the observed holographic contrast to that predicted from transmission ellipsometry measurements.