Canek Fuentes-Hernandez

High-performance photorefractive polymers sensitized by cadmium selenide nanoparticles

We report on efficient and fast hybrid photorefractive polymer sensitized with cadmium selenide (CdSe) quantum dots. The surface of the quantum dots was treated with 4-methylbenzenethiol. This surfactant is responsible for efficient photoinduced charge generation in the composite, leading to fast grating build-up times of 100ms and below. Overmodulation of the diffraction efficiency was observed at an applied field of 60V∕μm.

Stabilization of the response time in photorefractive polymers

The optical and photoconductive fatigue of fast photorefractive polymers have been studied in a family of C60-sensitized polymer composites containing styrene-based chromophores with varying ionization potential. Changes in response time and in photoconductivity were studied for exposures up to 104u2002J/cm2. Increasing the chromophore ionization potential beyond that of the polyvinylcarbazole host was found to stabilize the response time. Studies of the electric-field dependence of the steady-state diffraction efficiency in various samples confirm the role of C60 anions as possible traps.

Photorefractive polymers sensitized by two-photon absorption

We demonstrate the recording of holograms and their nondestructive readout in a photorefractive polymer, using two-photon absorption. Sensitivity is provided by the excitation of the electroactive chromophore with femtosecond pulses, followed by charge injection into the photoconducting poly(N -vinylcarbazole) matrix. The holograms can be fully erased with a pulsed laser source but are insensitive to cw laser beams with the same wavelength. Studies of the field and intensity dependence of the diffraction efficiency indicate that the holograms are formed through the photorefractive effect.

Video-rate compatible photorefractive polymers with stable dynamic properties under continuous operation

We report on photorefractive polymer composites that exhibit stable dynamic properties under continuous operation. These materials are based on a bis-triarylamine side-chain polymer matrix with a low ionization potential. The evolution of the response time for exposures up to 4kJ∕cm2 was studied and compared with that obtained in poly(n-vinylcarbazole) (PVK) based composites. In the composites, operational stability is combined with video-rate compatible dynamics, large dynamic range at moderate fields, and long shelf lifetimes.

Photorefractive Polymers with Non-Destructive Readout

Photorefractive polymers are suitable for real-time holographic applications. Since the recording and readout of a hologram is carried out with laser beams with the same wavelength, the readout process partially erases the stored information, a problem common to all current photorefractive materials and referred to as destructive readout. In this paper we describe photorefractive polymers that are sensitized by two-photon absorption. Holographic recording is achieved with high-intensity writing beams and readout using low light intensity, but high power beams. Using this nonlinear recording scheme, non-destructive readout was demonstrated.

Photorefractive polymer composites fabricated by injection molding

We report on the fabrication of bulk samples of photorefractive polymers using the injection molding technique. The photorefractive properties of these materials are evaluated by four-wave mixing and two-beam coupling experiments. Samples with good optical quality, high diffraction efficiency, and net optical gain are obtained.

Photorefractive polymers based on bis-triarylamine side-chain polymers

We report on the photorefractive properties of two polymer composites that utilize a new bis-triarylamine side-chain polymer matrix. Correctly locating the frontier orbitals of the new transport manifold with respect to the HOMO levels of chromophores, allows stable continuous operation over exposure levels of more that 4 kJ/cm2 when samples are electrically biased at 57 V/μm. This operational stability is combined with video-rate compatible grating build-up times and a dynamic range that allows index modulations of 3 x 10-3 and gain coefficients on the order of 100 cm-1 at moderate fields. The thermal stability of one of the composites reported is excellent, showing no signs of phase separation even after one week at 60°C. A comparison with the stability of composites where the new matrix was replaced by PVK is also presented.

Efficient photorefractive polymers sensitized by CdSe nanoparticles

We report on an efficient and fast hybrid photorefractive polymer sensitized with CdSe quantum dots. The surface of the quantum dots was treated with 4-methylbenzenethiol. This surfactant allows the quantum dots to have an efficient photoinduced charge generation when mixed with a mixture of chromophores. The enhanced photoconductive properties lead to fast grating build-up times of 100 ms and below. In four-wave mixing experiments, overmodulation of the diffraction efficiency was observed at an applied field of 60 V/μm and gain coefficients on the order of 20 cm-1 at moderate fields.

Trapping mechanisms and dynamics in bis-triarylamine-based photorefractive polymer composites

We report on the trapping mechanisms in bis-triarylamine (PATPD) based polymer composites. Although exceptional stability under continuous operation has been reported in PATPD-based composites, a small degradation of the response time in photorefractive devices under continuous operation has been found when improved styrene-based chromophores, with high figure-of-merit, are used. The accumulation of relatively large densities (~1017 cm-3) of filled traps is observed even though to first approximation the transport manifold has the lowest ionization potential of all the moieties in the composite, so no apparent deep trapping sites are to be present. The results of spectroscopic studies where the formation of chromophore aggregates is explored and correlated with the formation of hole-trapping sites that dominate the temporal evolution of the photogenerated current density and C60 anion accumulation after several minutes of continuous operation will be presented and compared with numerical simulations considering a two-trapping site model in materials containing the chromophore DBDC.

Efficient Green and Blue Electrophosphorescent Light-Emitting Diodes using a Combination of Solution and Vacuum-Processed Materials

The performance of organic light-emitting diode devices with a spin-coated hole-transporting layer and a thermally deposited emissive layer consisting of a bis-sulfone small molecule, as a host for the blue phosphorescent emitter will be presented.