Large three-photon absorption and intramolecular charge transfer of the bis-donor fluorene-based molecules

Three-photon absorption (3PA) of two fluorene-based molecules with D-pi-D structural motifs (abbreviated as BPAF and BCZF) has been determined by using a Q-switched Nd: YAG laser pumped with 38 ps pulses at 1064 nm in DMF. The measured 3PA cross-sections are 222 and 140 x 10(-78) cm(6) s(2) for BPAF and BCZF, respectively. AM1 calculations show that attaching different donors changes the charge density distribution of the fluorene skeleton, and it is observed that the 3PA cross-section can be enhanced with increasing intramolecular charge transfer character, measured by the parameter Delta p(1)/Delta p(2)/Delta p(1)'. (c) 2005 Elsevier B.V. All fights reserved.

Synthesis and Characterizations of Poly(9,10-bisarylethynyl-2,6-anthrylene)s and Poly(9,10-bisalkynyl-2,6-anthrylene)

A poly(9,10-bisalkynyl-2,6-anthrylene) (PI) and five poly(9,10-bisarylethynyl-2,6-anthrylene)s(P2-P6) as soluble conjugated polymers have been synthesized and characterized. All polymers exhibit two-dimensional conjugated characteristics as indicated by absorption spectra comprising multi-bands in the range of 300-600 nm. Compared with P1, polymers P2-P5, which contain phenylethynyl substituents with the longer conjugation than alkynyl groups, exhibit a similar to 60 nm red shift of absorption edge. However, further increasing the conjugation length of the arylethynyl substituents (longer than phenylethynyl) has only a no effect on the conjugation of the polymer chains, while comparing the absorption spectra of P6 with those of P2-P5.

Phase-dependent properties for absorption and dispersion in a closed equispaced three-level ladder system

It is shown that in a closed equispaced three-level ladder system, by controlling the relative phase of two applied coherent fields, the conversion from absorption with inversion to lasing without inversion (LWI) can be realized; a large index of the refraction with zero absorption can be gotten; considerable increasing of the spectrum region and value of the LWI gain can be achieved. Our study also reveals that the incoherent pumping will produce a remarkable effect oil the phase-dependent properties of the system. Modifying value of the incoherent pumping can change the property of the system from absorption to amplification and enhance significantly LWI gain. If the incoherent pumping is absent, we cannot get any gain for any value of the relative phase. (c) 2007 Elsevier GmbH. All rights reserved.

Absorption and luminescence of the surface states in ZnS nanoparticles

A broad absorption band around 500 nm is observed in ZnS nanoparticles. The absorption becomes more intensive and shifts to the blue as the particle size is decreased. The absorption energy is lower than the band gap of the particles and is considered to be caused by the surface states. This assignment is supported by the results of the fluorescence and of the thermoluminescence of the surface states. Both the absorption and the fluorescence reveal that the surface states are size dependent. The glow peak of the semiconductor particles is not varied as much upon decreasing size, indicating the trap depth of the surface states is not sensitive to the particle size. Considering these results, a new model on the size dependence of the surface states is proposed, which may explain our observations reasonably. (C) 1997 American Institute of Physics.

Absorption and Raman spectra of Se-8-ring clusters in zeolite 5A

Samples with different weight ratio of Se to zeolite 5A (Se composition) have been prepared by loading Se into the cages of zeolite 5A and the measurements of the absorption and Raman spectra have been carried out for the prepared samples. The measured absorption edges of the samples close and blue shifted to the value for monoclinic Se containing Se-8-ring, suggesting the formation of Se-8-ring clusters dagger in the cages. The continuous and broadening features of the absorption spectra are interpreted by the strong electron-phonon coupling in Se-8-ring clusters. The sample with high Se composition has a red shift of the absorption band edge relative to the samples with less Se composition. It is tentatively attributed to the reason that with different Se composition, single Se-8-ring clusters and double Se-8-ring clusters are formed in the cages of zeolite 5A. A single broad band at about 262 cm(-1) is observed in the Raman spectra, that gives the further support of the formation of Se-8-ring clusters. Copyright (C) 1996 Elsevier Science Ltd

Injection, Transport, Absorption and Phosphorescence Properties of a Series of Blue-Emitting Ir(III) Emitters in OLEDs: a DFT and Time-Dependent DFT Study

Quantum-chemistry methods were explored to investigate the electronic structures, injection and transport properties, absorption and phosphorescence mechanism of a series of blue-emitting Ir(III) complexes {[(F-2-ppy)(2)Ir(pta -X/pyN4)], where F-2-ppy = (2,4-difluoro)phenylpyridine; pta = pyridine-1,2,4-triazole; X = phenyl(1); p-tolyl (2); 2,6-difluororophenyl (3); -CF3 (4), and pyN4 = pyridine-1,2,4-tetrazolate (5)}, which are used as emitters in organic light-emitting diodes (OLEDs). The mobility of hole and electron were studied computationally based on the Marcus theory. Calculations of Ionization potentials (IPs) and electron affinities (EAs) were used to evaluate the injection abilities of holes and electrons into these complexes.

Synthesis and characterization of Y0.9-xGdxEu0.1BO3 phosphors by spray drying process

Y0.9-xGdxEu0.1BO3 phosphors were synthesized by spray drying (SD) method, and the results were compared with those by conventional solid state (SS) and citrate gel (GC) methods. The PL intensity of phosphors increases with the increase of x value in Y0.9-xGdxEu0.1BO3 (prepared by SD) due to an energy migration process like Gd3+ - (Gd3+)(n) - Eu3+ occurred in the material. Compared with the latter two methods, the phosphor particles prepared by spray drying method have a better morphology, such as homogeneous size (about 1similar to3 mum) with spherical shape and smooth surface. Furthermore, the spray drying-derived phosphors have higher photoluminescence (PL) intensity than those by citrate gel method, but still a little lower than those by the solid state method.

Attenuation of photosynthetically available radiation by chlorophyll, chromophoric dissolved organic matter, and tripton in lake Donghu, China

The attenuation coefficient of photosynthetically available radiation [K-d(PAR)] and three water quality parameters [chlorophyll a (chl a)], chromophoric dissolved organic matter (CDOM) and tripton] were measured at three stations in shallow, subtropical Lake Donghu from April 2003 to March 2004. The multiple regression equation of K-d(PAR) versus chl a, CDOM, and tripton was: K-d(PAR) = 0.44 + 0.019 chl a + 1.88 CDOM + 0.016 tripton, which revealed the relative contributions of the three parameters to K-d(PAR). The effects of water and CDOM on K-d(PAR) were of minor importance (19-26%), while chl a and tripton were the two greatest contributors, accounting collectively for 74-81%.

Linear and nonlinear optical properties of the PbSe quantum dots doped germane-silica glass optical fiber

We report development of a new fiber doped with PbSe quantum dots for nonlinear optical applications. PbSe quantum dots related absorption peaks were obtained at 1021, 1093 and 1351 nm. The resonant optical nonlinearity and attenuation at 1500 nm were measured to be 9.4 × 10−16 m2/W and 0.01 dB/m, respectively. The emission around 1540 nm was observed upon near resonant pumping at 1064 nm.

Hole-transporting polymers containing carbazol-3,9-diyl and 1,4-phenylene fragments in the main chain

New carbazole-based polymers, which contain various content of electro-active fragments in the main chain connected via alkylene spacers, have been synthesized by Ni(0)-catalyzed Yamamoto-type aryl-aryl coupling reactions. These compounds represent amorphous materials of high thermal stability with glass-transition temperatures of 139-151 degrees C and thermal decomposition starting at temperatures above 400 degrees C. UV-vis absorption and photoluminescence emission spectra of the materials confirmed that the conjugated segments in the macromolecules are rather short.

Synthesis and chain-length dependent properties of monodisperse oligo(9,9-di-n-octylfluorene-2,7-vinylene)s

A series of monodisperse oligo(9,9-di-n-octylfluorene-2,7-vinylene)s (OFVs) with fluorene units up to 11 has been synthesized following a divergent approach. Chain length was found to affect not only photophysical properties but also thermal properties. Absorption and photoluminescence spectra are red-shifted with increasing chain length. The effective conjugated length has been extrapolated to be as long as 19 fluorene vinylene units, indicative of a well-conjugated system. With the number of fluorene units > 5, the oligomers exhibit nematic mesomorphism. Glass transition temperature (T-g) and clearing point temperature (T-c) increase with increasing molecular length and with those of OFV11 up to 71 and 230 degrees C, respectively. The oligomers can form uniform films by solution casting for fabrication of light-emitting diodes. With a device structure of ITO/ PEDOT:PSS/OFV11/Ca/Al, a current efficiency of 0.8 cd.A(-1) at a brightness of 1300 cd.m(-2) along with a maximum brightness of 2690 cd.m(-2) have been realized. This performance is notably superior to that of the corresponding polymer.