G. J. Zhang

Efficient organic red electroluminescent device with narrow emission peak

We report a red fluorescent material of 3-(dicyanomethylene)-5,5-dimethyl-1(4-dimethylamino-styryl)cyclohexene (DCDDC) and its use as emitter or dopant in tris-(8-hydroxyquinoline) aluminum based electrolumiescent (EL) devices. The DCDDC was synthesized by a simple “one-pot” reaction and shows bright red photoluminescence with a peak wavelength at 650 nm. EL properties of double-layer light-emitting diodes of indium tin oxide (ITO)/poly(N)-vinylcarbazole (PVK):N,N′-diphenyl-N,N-bis(3-methylphenyl)1,1–biphenyl-4,4′-diamine (TPD)/DCDDC/Mg:Ag and ITO/PVK:TPD/DCDDC(1%):Alq3/Mg:Ag using DCDDC as red emitters or dopants were characterized. The device with 1% DCDDC-doped Alq3 as emitting layer has a turn-on voltage of 5 V, and the highest luminance of 5600 cd/m2 is obtained at 15 V. The EL efficiency of the device at 100 cd/m2 is in the range of 1.1 l m/W, and the highest EL efficiency is 1.6 l m/W. The devices emit in the red region, and the full width at half maximum of the EL spectra is 70 nm.

Measuring anisotropic refractive indices and film thicknesses of thin organic crystals using the prism coupling method

Anisotropic refractive indices of the organic biaxial thin-film crystal, 2-methyl-4-nitroaniline (MNA), were determined by the prism coupling method. The experiment was carried out on an anisotropic waveguide of the MNA monocrystal film by an incorporated analysis of the TE and TM waves.

Nonlinear optical materials derived from biopolymer (DNA)-surfactant azo dye complex

This paper reports on optical and optoelectronic properties of DNA-surfactant complex films which were intercalated with a NLO dye, Disperse Red 13(DR-13). Circular dichroism (CD) analysis indicated that the orientation of the azo dye, DR-13 doped in DNA-surfactant complex film was achieved by inserting the dye molecules into the nano-size space between base pairs of DNA. The Disperse Red 13-doped DNA thin film displayed higher THG than that of CS2 about two orders. On the other hand, SHG signal could not be observed even in the presence of anisotropic ordering of the molecular chromospheres on template of the double helix of DNA, perhaps because of absorption of the dye for SHG light.

Optical quadratic nonlinearity in multilayer corona-poled glass films

Second order nonlinearity via corona poling at room temperature in a Corning 7059 glass film on a Pyrex glass substrate was studied. It was clearly pointed out that the origin of the induced nonlinearity in this waveguide was located at the interface region between a top layer glass film and a glass substrate. This region is formed to be a depletion layer in the consequence of a drift of positive ions towards a negative electrode during corona poling. X‐ray photoelectron spectroscopy measurement on the corona‐poled Pyrex glass substrate gave the evidence that the main mobile ions were sodium ions.

Second‐harmonic generation of a new chalcone‐type crystal

A new type of chalcone crystal was prepared. Anisotropic indices with wavelength dispersion were measured by the Brewster angle method. The two largest second‐harmonic generation (SHG) tensor components were determined by the wedge method and compared with d11 of 2‐methyl‐4‐nitroaniline. Calculated collinear and noncollinear phase‐matched SHG patterns reasonably fit the observed photographs.

Second order nonlinear optical properties in silica-based glass film waveguides

Phase-matched blue second harmonic generation was observed in a corona-poled Corning 7059 glass film waveguide. The induced quadratic optical nonlinearity was examined by second harmonic generation with a time dependent decay for multi-complex of SiO2,BaO,B2O3 and/or Al2O3. Glass films with every possible combination of composition were fabricated and examined, The glass composition of SiO2-BaO-B2O3 and/or SiO2-BaO-Al2O3 was found to play effective roles in maintaining the induced second order nonlinearity for a longer period of time. This is supposed to be related to distributed traps which come from complex of the glass components.

Time-dependent decay of quadratic non-linearity in corona-poled silicate glass films

Abstract Quadratic optical effects in corona-poled silicate glass films on glass substrates were investigated using second harmonic generation. A time-dependent decay of the quadratic non-linear coefficients observed at room temperature was found to be composed of two components which have different relaxation times. The slow decay component increased with an increase of BaO-B 2 O 3 or BaO-Al 2 O 3 in the glass composition and with a decrease in the film thickness. The quadratic non-linearity showing the slow decay is assumed to be ascribed to a microscopic change in a local structure of the glass films. On the other hand, the fast decay component is suggested to be caused by a static-electric field in the entire film which formed by the induced surface charge and the space charge at the interface between the film and the substrate.

Strongly luminescent rare-earth-ion-doped DNA-CTMA complex film and fiber materials

A rare-earth chelate, Europium 6,6.7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5,-octanedionate, (Eu3+-FOD) doped DNACTMA complex as fiber and film materials was prepared by casting solution method and gel-spinning method. The Eu-FOD-DNA-CTMA complex was luminescent and has 750 μs of fluorescence lifetime, sharply-spiked emission spectra, excellent film and fiber formability, moderate absorption (40000M-1cm-1) at 327 nm and high quantum yield forlanthanide emission. By comparison of fluorescence lifetime of Eu-FOD doped DNA-CTMA solid matrix with that of Eu-FOD doped in PMMA, it was clear that energy transfer from DNA to FOD leads to enhancement of fluorescence emission at 613 nm. Analysis results for fluorescence spectra and fluorescence relaxation time of Eu3+ doped in the materials indicated that Eu3+-FOD is chemically bond within the DNA-CTMA matrix. Amplified spontaneous emission (ASE) at 612 nm by pumping with UV laser (355 nm) was observed in the materials. Fluorescence lifetime of the Eu-FOD doped in the DNA-CTMA solid matrix was evaluated to be 750 μs, which is ca. 230μs longer than that of Eu-FOD doped in PMMA solid matrix. Efficient Energy transfer from base of DNA to FOD, then to Eu, occurred when irradiated by UV light or 355 laser beams.

Optical properties of photochromic-compound-doped marine-biopolymer DNA-surfactant complex films for switching applications

Optical properties of spiropyran-doped DNA-CTMA films have been studied. They strongly depended on molar ratio of DNA/spiropyran. Switching experiments was performed for 1.55-μm signal light. Measured slow transition times indicate much precise adjustment and optimization.

Theoretical analysis of the spatial phase-matching loci for second-harmonic generation and multiwave-mixing interactions.

We report a theoretical analysis on spatial noncolinear phase matching of multiwave mixing and its application to a second-harmonic-generation (SHG) experiment. From the numeric calculations, the noncolinear phase-matching properties in general situations were determined. The theory gives the applicability for all noncolinear phase matching. Fine coincidences between theoretical calculations and observed spatial loci on noncollinear phase-matching SHG were confirmed. Relations that allow the calculation of the noncollinear phase-matching angle for any case of SHG are established. As an example, the noncolinear phase-matched SHG pattern on a screen is calculated numerically in the case of SHG of 1064 nm from a Nd:YAG laser under the phase-matched condition for two organic nonlinear crystals: 1-(2-thienyl)-3-(4-methyphenyl) propene-1 (TC-28), which is biaxial, and (2-furyl) methacrylic anhydride (FMA), which is uniaxial. Experimental results compared quite favorably with the theoretical analysis. Noncolinear phase matching may be of great practical interest in optical multiwave-mixing processes, such as optical parametric oscillation and optical parametric amplification. This technique also can be used for the measurement of crystal optical constants.