Jian-Yang Cho

Highly efficient green phosphorescent organic light-emitting diodes with simplified device geometry

We report on the performance of green phosphorescent organic light-emitting diodes based on the well-known host 4,4′-di(carbazol-9-yl)-biphenyl and the green phosphor emitter fac tris(2-phenylpyridinato-N,C2′) iridium. Using a spin-coated hole-injection/transport layer of poly(N-vinyl-carbazole) and a hole-blocking/electron-transport layer of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, devices with efficiencies of 21.2% and 72cd∕A at 100cd∕m2 were obtained in a simplified device geometry that requires the deposition of only two organic layers from the vapor phase.

Strong two-photon absorption at telecommunications wavelengths in nickel bis(dithiolene) complexes

The two-photon absorption spectrum of a nickel bis(dithiolene) complex with extended conjugation and pi-donor substitution is measured by using Z-scan and pump-probe techniques with femtosecond pulses over the spectral range from 1.20 to 1.58 microm, which includes much of the telecommunications range. The peak two-photon cross section of over 5000 GM (1 GM = 10(-50) cm4 s photon(-1) molecule(-1)) occurs at approximately 1.24 microm, with significant two-photon absorption (>440 GM) throughout the spectral range examined.

Synthesis of a Nickel Bis(dithiolene) Complex with Strong Near-Infrared Two-Photon Absorption

The diketones 4,4′-di[3,4-bis(n-dodecyloxy)styryl]benzil and 4,4′-di[3,4-bis(n-dodecyloxy)phenylethynyl]benzil have been synthesized from 4,4′-dibromobenzil using Heck coupling with the appropriate styrene and Sonogashira coupling with the appropriate phenylalkyne, respectively. Treatment of the distyrylbenzil derivative with phosphorus pentasulfide followed by nickel(II) chloride gave the corresponding extended nickel bis(dithiolene) derivative which shows strong near-infrared two-photon absorption with a cross-section of over 440 GM (1 GM = 10−50 cm4 s photon−1 molecule−1) throughout the telecommunications range and a peak cross-section of 5300 GM at ca. 1.2 μm.

Linear and nonlinear optical properties of highly transmissive one-dimensional metal-organic photonic bandgap structures

We present the design, fabrication and characterization of the optical properties of one-dimensional metal-organic photonic bandgaps (MO-PBGs) composed of a tetraphenyldiaminobiphenyl-based polymer and ultrathin electrically continuous Cu layers. The fabricated MO-PBGs achieve a peak transmission of around 44% at 620 nm combined with very large spectral, around 120 nm FWHM, and angular, more than 120° field-of-view, bandwidths. Using 140 fs pulses at various wavelengths we have found up to 10 × enhancements in the nonlinear optical (NLO) properties of the MO-PBGs when compared with the NLO response of ultrathin electrically continuous Cu layers.

Processible Polyacetylene-Based χ (3) Materials for Photonic Applications

A number of processing variations were carried out to optimize the morphology, third- order nonlinearity, and processability of substituted polyacetylene polymers. This allowed for spin coating of optical quality films with large nonlinearities.

Toward the realization of practicable materials for χ (3) based photonic applications

Two different routes were taken to develop materials for use in all-optical signal processing applications. Both systems exhibited large ultrafast nonlinearities, transparency in the near-infrared, and good processability for integration into photonic devices.