Experimental and Theoretical Study on Terahertz Spectra for Regenerated Cellulose.

In this work, regenerated cellulose films were prepared with an iced dissolution method, while the physical morphologies and crystal types of the products were systematically characterized with scanning electron microscope (SEM), Fourier transform infrared(FTIR), while X-Ray Diffraction (XRD). The results demonstrate that the as-prepared continuous and uniform films are indeed cellulose Ⅱ, whose morphology and crystal type are significantly different from those of the degreased cotton. Moreover, Terahertz time domain system (THz-TDS) and FTIR were employed to measure the THz spectra of the regenerated cellulose films. Accordingly, the THz characteristic peaks for the regenerated cellulose films are experimentally identified for the first time. In addition, the increase of the THz transmittance with the decrease of the wavenumber is attributed to the existence of amorphous components in the regenerated cellulose films. Although the shapes of Far-IR spectra in the range of 100～700 cm-1 are similar, the absorption peaks of the regenerated cellulose films move to lower wavenumbers (blue shift) compared with those of the degreased cotton. Based on this, we developed a new approach to distinguish the allomorphism of cellulose Ⅱ and cellulose Iß by Far-IR. Particularly, geometry optimization and IR calculation for the crystal structure of cellulose Ⅱ have been successfully processed by Density Functional Theory (DFT) using periodic boundary condition via CASTEP package. The calculated absorption peak positions are in good agreement with those experimentally measured. Consequently, the THz characteristic peaks of the regenerated cellulose films have been systematically and successfully assigned. Theoretical calculations reveal that the peaks at 42 and 54 cm-1 are assigned to the lattice vibration modes coupled with translational mode and rotational mode, respectively. Moreover, the absorption peaks in the range of 68～238 cm-1 are related with the torsion vibration of ­CH2OH group and deformation vibration of C­H bond and O­H bond, while those in the range of 351～583 cm-1 are assigned to the skeletal vibration of C­O­C bond and pyranoid ring, and those at 611 and 670 cm-1 are originated from the out-of-plane bending vibration of O­H bond. Each absorption peak is involved in more than single vibration mode. The THz spectra presented in this work, together with the theoretical simulations, indicate that the THz responses of regenerated cellulose are closely associated with both its chemical constituents and molecular structure. These results will be helpful not only for better understanding the relations between the molecular structure of the regenerated cellulose and its THz spectrum, but also for providing valuable information for future studies on the physical mechanisms of THz responses of other partially-crystalline polymers and organic biological macromolecules.

[Study on Characteristics of Terahertz Spectra of Organic Functional Groups].

Fourier transform infrared (FTIR) was exploited to measure terahertz (THz) spectra in the wave number range of 30-300 cm(-1) for saturated straight chain organic molecules at room temperature. The results reveal that different organic functional groups exhibit different THz spectral characteristics. The absorption peaks of vibration modes of organic crystal lattice locate in high frequency range of THz, while those of vibration modes of intermolecular hydrogen (H) bonds appear in low frequency range of THz. Moreover, a typical absorption peak of intermolecular H bonds caused by saturated straight-chain monohydric alcohol hydroxyl functional groups locates at 57 cm(-1), while a characteristic absorption peak of intermolecular hydrogen bonds caused by triacontanoic acid carboxyl functional groups appears at 74 cm(-1). The intermolecular H bonds not only result in that the THz absorbing abilities of triacontanol and triacontanoic acid are significantly stronger than that of triacontane, but also cause regular red-shift and blue-shift of the THz absorption peaks of triacontanoic acid, as compared with those of triacontanol. In addition, density functional theory (DFT) B3LYP/6-311G(d,p) basis set was employed to simulate the THz spectra of saturated straight-chain alkane, alkanol and acid, respectively. The simulation results indicate that for the organic molecules with stronger intermolecular H bonds, lower consistent degree of the THz spectrum simulated from monomer molecule with the THz spectrum experimentally measured will occur. Moreover, the simulation results of dimer structures agree well with the measured spectra as compared to those simulated from monomer molecule structures. The results presented in this work are of great significance not only to the study of the THz spectral characteristics of other organic functional groups, but also to the clarification of the vibration modes of organic molecules. Particularly, our results are also helpful for clarifying the THz response theory of organics, and for exploiting the applications of organic materials in THz devices.

[Advances in infrared spectrum zoom imaging system research].

Compared with the infrared spectrum fixed focal length system and infrared spectrum dual-zoom system, infrared spectrum continuous zoom imaging system which has continuous variational field of view can track targets sequentially, so it is a research direction in infrared spectrum imaging technology. Some new technologies are presented overseas in order to improve the detection performance, reduce cost and have good athermalized performance in infrared spectrum continuous zoom imaging system. Infrared material, infrared detector and variable aperture, those new technologies are su mmarized and the idiographic application of those new technologies in infrared spectrum continuous zoom imaging system are presented in the paper, for example athermalization of an infrared spectrum zoom lens system with new infrared material for target detection, dual band infrared spectrum continuous zoom imaging system with mid-wave infrared and long-wave infrared, infrared spectrum continuous zoom imaging system with high ratio, nfrared spectrum continuous zoom imaging system with dual F/number. It is useful for the development of chinese infrared continuous zoom imaging system.

[Design and study of middle infrared spectrum system with variational field of view].

In order to track and capture target at the same time with a set of equipment, a middle infrared spectrum variational field of view (fov) detection system with a large focal plane array was designed for a 640 x 512 novel large focal plane array infrared detector with the picture element size of 15 m x 15 m. The spectrum range was 3.7-4.8 m, F number was 4.0, narrow FOV and wide FOV was 0.45 and 0.90 respectively. The manner of variational FOV was accomplished by pitching two lenses into the narrow FOV system layout with mechanism framework. Reimaging technology not only minished the diameter of front fixed group, but also met 100% cold shield efficiency to minish stray light into the infrared detector. Two common infrared materials Ge and Si were used in the variational FOV detection system. The aspheric technology was used in order to correct the off axis aberration and higher order aberration and assure the fixedness of image plane. At the spatial frequency 33 lp x mm(-1), the modulation transfer function(MTF) was above 0.2 for both the narrow FOV and wide FOV. Moreover, the distortion is below 0.5%. The middle infrared spectrum variational FOV detection system has excellent image. The image quality of the middle infrared spectrum variational field of view detection system changed little in the working temperature range -35-55 degrees C.

[Electroluminescent performance and spectral characteristics of a novel (t-bt)2Ir(acac) phosphorescent iridium complex].

The photoluminescence (PL) spectra and UV-Visible absorption spectra of a novel yellow phosphor dye of bis[2-(4-tert-butylphenyl)benzothiazolato-N,C2'] iridium (acetylacetonate) denoted as (t-bt)2Ir(acac) were systematically investigated, which were measured in solution and film states with various concentrations. The results showed that the highest PL intensity was achieved when the solution concentration was 3 x 10(-4) mol L(-1), and it decreased dramatically when the concentration kept on increasing because of concentration quenching of the phosphor dye. A red shift for PL spectra and UV-Vis absorption spectra of films compared to those of solutions were found, which is due to the shorter distance, aggregation effect, and stronger interaction of dye molecules in solid state. Based on the spectrum characterization, organic light-emitting diode was fabricated with an ultrathin structure based on this phosphor dye, which showed a high luminescence of 18 367 cd m(-2) at a bias of 13.2 V.

[Spectral characteristics of novel small molecular fluorene derivative for organic light-emitting device].

Double-layer organic light-emitting devices (OLEDs) based on a blend system of novel small molecule fluorene material 6,6'-(9H-fluoren-9,9-diyl) bis(2,3-bis(9,9-dihexyl-9H-fluoren-2-yl) quinoxaline) (BFLBBFLYQ) and hole transporting material N, N'-biphenyl-N, N'-bis-(3-methylphenyl)-1, 1'-biphenyl-4, 4'-diamine (TPD) were fabricated. The structure of the double-layer device was ITO/BFLBBFLYQ : TPD/tris(8-hydroxyquinolinato) aluminum(Alq)/Mg : Ag. The photoluminescence (PL) spectra of BFLBBFLYQ and TPD were located at 447 and 414 nm, respectively. The spectral characteristics of the blend system and the double-layer device were investigated, which indicated that a new long wavelength emission peaking at 530 nm was appeared both in PL spectra and electroluminescence (EL) spectra. The exciplex between BFLBBFLYQ and TPD may play the role in long wavelength emission in the blend device and the spin-coated film. Based on the absorption spectra of a red fluorescent dye 4-(dicyanomethylene)-2-tert-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as probe and the PL spectra of the blend system showing good overlap, energy transfer from the blend system to DCJTB could be expected. There fore, DCJTB could be selected as a molecular dopant to investigate the influence on EL spectra and the recombination of the devices. It was found that the excitons recombine at the interior Alq layer near to the BFLBBFLYQ : TPD layer.

[Spectral characteristics of white organic light-emitting devices based on a novel nitrile fluorescence dye].

A white organic light-emitting device with a blend polymeric emissive system consisting of a novel nitrile fluorescence (2Z, 2'Z)-3, 3'-(1,4-phenylene)bis(2-phenylacrylonitrile) (BPhAN) as dopant and poly(N-vinylcarbazole) (PVK) as host was fabricated. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was introduced into bilayer device as an electron transporting layer (HTL) and a hole blocking layer (HBL), respectively. By adjusting the doping ratio of BPhAN, a series of devices with different concentration proportion of PVK : BPhAN were constructed. The photoluminescence (PL) and electroluminescence (EL) characteristics of the devices were systemically studied. The Förster energy transfer mechanisms and direct carrier trapping mechanisms were specially investigated. The results showed that effective Förster energy transfer from PVK to BPhAN existed in the blending system as well as carrier trapping. However, at the identical bias voltage, the performance of devices was affected mainly by the carrier trapping mechanisms. Nevertheless, at different bias voltages, the performance of devices was affected by both of the two mechanisms. When the doping ratio of BPhAN reached 4 wt%, bright white light was obtained. The peaks of EL spectra were located at 425 and 556 nm corresponding to the Commissions Internationale De L'Eclairage (CIE) coordinates of (0.33, 0.37) at 6 V and (0.32, 0.33) at 16 V, respectively. The slight shift of CIE coordinates was attributed to that energy transfer probability from PVK to BPhAN and BPhAN charge carrier trapping efficiency both decreased with the increase in voltages.

[Fluorescence spectra of rubrene dopant for organic light-emitting devices].

The effect of concentration of 5, 6, 11, 12-tetraphenylnaphthacene (rubrene) yellow dye in solution on fluorescence performance was studied through various concentrations. Also the photoluminescence (PL) spectra of rubrene solution with various concentrations were measured to investigate the concentration effect, which is beneficial to obtaining an optimum concentration at maximum PL intensity without concentration quenching. One hand was to focus on the range of concentration for quenching. The other hand was to change the solution concentration in the range of concentration. The results showed that the PL intensity was the highest at a rubrene concentration of 2 x 10(-3) mol x L(-1), which was fixed on a concentration range from 10(-3) to 10(-2) mol x L(-1). And it was decreased only 11% with the increase in concentration after the optimum concentration. The PL spectra of rubrene: N,N'-Bis(naphthalen-1-y)-N,N'-bis(phenyl)benzidine (NPB) blending system with various proportions in solution were also measured, indicating that the inefficient energy transfer between NPB and rubrene leads to white fluorescence light emission. It was better to realize blue and yellow fluorescence from NPB and rubrene, so the white light was obtained.

[Influence of fluorescent dye ultrathin layer on luminescence spectra in organic light-emitting diodes].

By using an ultrathin dopant dye layer deposited on the top of host materials, the influence of concentration of three fluorescent dyes, dimethylquinacridone (DMQA), 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), and 5,6,11,12-tetraphenylnaphthacene (rubrene), on the luminescence spectra of OLEDs was studied. The characteristic of the brightness-efficiency-bias voltage performance was investigated. The results showed that compared to the conventional doping devices, the devices consisting of ultrathin dye layer exhibited a weak peak originating from host matrix, and the more obvious concentration quenching was existent. The degree of concentration quenching for the three ultrathin doping dyes from high to low is in the order of DMQA, DCJTB and rubrene. Meanwhile, the authors used the photoluminescence spectra of these three dopants dilute solution to testify the relationship between EL properties of OLEDs and concentration quenching of these dyes.