Blue amplified spontaneous emission from 2, 1, 3-benzothiadiazole attached polyfluorene semiconductor polymer with high photoluminescence efficiency

The amplified spontaneous emission properties of a 2, 1, 3-benzothiadiazole attached polyfluorene semiconductor polymer were studied. The conjugated polymer shows a high photoluminescence quantum efficiency of 67% and emits a narrowed blue emissive spectrum with a full width at half-maximum of 3.6 nm when optically pumped, indicating better lasing action. A threshold energy as low as 0.22 mJ pulse(-1) cm(-2), a net gain of 40.54 cm(-1) and a loss of 7.8 cm(-1) were obtained, demonstrating that this conjugated polymer could be a promising candidate as the gain medium for the fabrication of blue polymer lasers.

Enhanced amplified spontaneous emission using layer-by-layer assembled cowpea mosaic virus

Layer-by-layer assembly technique was used to construct ultrathin film of cowpea mosaic virus (CPMV) by electrostatic interactions, and the film was employed as a precursor on which an OF8T2 film was deposited by spin coating. Amplified spontaneous emission (ASE) was observed and improved for the OF8T2 film. Compared with OF8T2 film on quartz, the introduction of CPMV nanoparticles reduced the threshold and loss, and remarkably increased the net gain. The threshold, loss, and gain reached 0.05 mJ/ pulse, 6.9 cm(-1), and 82 cm(-1), respectively. CPMV nanoparticles may enormously scatter light, resulting in a positive feedback, thus the ASE is easily obtained and improved.

Templated assembly of mu(5)-CO32- decanuclear praseodymium and neodymium clusters through spontaneous fixation of atmospheric carbon dioxide

Reactions of Ln(III) acetate (Ln = Pr and Nd) and a polydentate Schiff-base in a mixture of methanol and acetonitrile resulted in the unprecedented assembly of novel Ln(10) aggregates containing two Ln(5) pentagons templated by mu(5)-CO32-, introduced via spontaneous fixation of atmospheric carbon dioxide. Magnetic analysis using an expression including the ligand field effects and molecular field approximation indicates weak antiferromagnetic coupling between the metal ions. This synthetic approach may represent a promising new route toward the design of new lanthanide clusters and novel multifunctional materials.

Spontaneous formation of two-dimensional gold networks at the air-water interface and their application in surface-enhanced Raman scattering (SERS)

Two-dimensional (2-D) gold networks were spontaneously formed at the air-water interface after HAuCl4 reacted with fructose at 90 degrees C in a sealed vessel, in a reaction in which fructose acted as both a reducing and a protecting agent. Through fine-tuning of the molar ratio of HAuCl4 to fructose, the thus-formed 2-D gold networks can be changed from a coalesced pattern to an interconnected pattern. In the coalesced pattern, some well-defined single-crystalline gold plates at the micrometer-scale could be seen, while in the interconnected pattern, many sub-micrometer particles and some irregular gold plates instead of well-defined gold plates appeared. It is also found that the 2-D gold networks in the form of an interconnected pattern can be used as substrates for surface-enhanced Raman scattering (SERS) because of the strong localized electromagnetic field produced by the gaps between the neighboring particles in the 2-D gold networks.

Improvement of amplified spontaneous emission performance by doping tris(8-hydroxyquinoline) aluminum (Alq3) in dye-doped polymer thin films

A well-known red fluorescent dye 4-(dicy-anomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB) was codoped with an electron transport organic molecule tris(8-hydroxyquinohne) aluminum (Alq3) in a host matrix of polystyrene (PS), and the amplified spontaneous emission (ASE) was studied by optically pumping. It was found that the ASE performance was significantly improved by the introduction of Alq3. The Alq3:DCJTB:PS blending thin films showed a low threshold (2.4 mu J/pulse) and a high net gain coefficient (109.95 cm(-1)) compared with the pure DCJTB:PS system (threshold of 15.2 mu J/pulse and gain of 35.94 cm(-1)). The improvement of the ASE performance was considered to be attributable to the effective Foster energy transfer from Alq(3) to DCJTB. Our results demonstrate that the Alq(3):DCJTB could be a promising candidate as gain medium for red organic diode lasers.

Improved amplified spontaneous emission by doping of green fluorescent dye C545T in red fluorescent dye DCJTB : PS polymer films

Amplified spontaneous emission (ASE) characteristics of a red fluorescent dye, 4-(dicy-anomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), and a green fluorescent dye, (10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1] benzopyrano [6,7,8-ij]quinohzin-11-one) (C545T) codoped polystyrene (PS) as the active medium were studied. It was found that the performance of ASE is greatly improved due to the introduction of C545T. By optimizing the concentrations of C545T and DCJTB in PS, an ASE threshold of 0.016 mJ pulse(-1), net gain of 52.71 cm(-1), and loss of 11.7 cm(-1) were obtained. The efficient Forster energy transfer from C545T to DCJTB was used to explain the improvement of the ASE performance in the coguest system.

Synthesis of a novel electroactive ABA triblock copolymer and its spontaneous self-assembly in water

An electroactive triblock copolymer of poly(ethylene glycol) (PEG) and aniline pentamer (AP), PEG-block-AP-block-PEG (PAP), was synthesized via polycondensation in the presence of N,N'-dicyclohexylcarbodiimide (DCC). The UV-vis spectra and cyclic-voltammograms (CV) spectra exhibited an excellent electroactivity of the triblock copolymer. The amphiphilic triblock copolymer self-assembles spontaneously into uniform micellar aggregates when the triblock copolymer was added directly to the aqueous solution. The size of the aggregates can be changed with the oxidation state of the AP segment in the PAP copolymer and the aggregates were pH-sensitive to the surrounding water solution, which provides a potential application in controlled drug release.

Synthesis of tellurium nanorods via spontaneous oxidation of NaHTe at room temperature

Trigonal phase of tellurium (t-Te) nanorods with tapered ends have been synthesized through spontaneous oxidation of NaHTe by dissolved oxygen at room temperature. Utilization of sodium dodecyl benzenesulfonate was found to help to obtain high-quality nanorods. The product was characterized by X-ray diffraction and Transmission electron microscopy. In addition, the possible nucleation and growth mechanism of the t-Te nanorods was discussed.

Hydrothermal synthesis and crystal structure of a sulfur-bridged binuclear copper(II) coordination polymer generated by a spontaneous reduction

A simultaneous reduction SO42- to S2- by 2,5-pyridinedicarboxylate under hydrothermal conditions produced a new binuclear copper(II) coordination polymer [CuS(4,4'-bipy)](n) (4,4-bipy = 4,4'-bipyridine) (1). Single crystal X-ray analysis revealed that compound I consisted of sulfur-bridged binuclear copper(II) units with Cu-Cu bonding which were combined with 4,4-bipy to generate a three-dimensional network constructed from mutual interpenetration of two-dimensional (6,3) nets. Crystal data for 1:C10H8CuN2S, tetragonal 14(1)/acd, a = 14.0686(5) Angstrom, b = 14.0686(5) Angstrom, c = 38.759(2) Angstrom, Z = 32. Other characterizations by elemental analysis, IR, EPR and TGA analysis were also described in this paper.

Amplified spontaneous emission and gain from optically pumped films of dye-doped polymers

The amplified spontaneous emission and gain characteristics of various fluorescent dyes, 2-(1,1-dimethylethyl)-6(2-(2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H-benzo[ij] quinolizin-9-1)ethenyl)-4H-pyran-4-ylidene) propanedinitrile (DCJTB) and 4-dicyanomethylene-2-methyl-6-(p-dimethyl-aminostyryl)-4H-pyran (DCM), doped in polystyrene (PS) matrices were studied and compared. It was found that DCJTB has a larger net gain, 40.72 cm(-1), a lower loss, 2.49 cm(-1), and a lower threshold, 0.16 (mJ/pulse)/cm(2), than DCM, which has a net gain of 11.95 cm(-1), a loss of 9.25 cm(-1), and a threshold of 4(mJ/pulse)/cm(2). The improvement of performance in DCJTB PS films is attributed to the larger free volume of DCJTB caused by the introduction of steric spacer groups into the DCJTB molecule.

Low threshold amplified spontaneous emission based on coumarin 151 encapsulated in mesoporous SBA-15

Amplified spontaneous emission (ASE) characteristics of a blue dye coumarin 151 encapsulated in a highly ordered mesoporous SBA-15 were studied. The spectra narrowing was observed and found that the threshold and loss were greatly reduced, and the gain is significantly increased compared with spin-coated coumarin 151 doped poly(4-vinylphenol) film. The ASE threshold, gain, and loss, respectively, reached 0.55 mJ pulse(-1) cm(-2), 44.78 cm(-1), and 8.9 cm(-1) for the coumarin 151 encapsulated in mesoporous SBA-15 film. The optimized lasing action owes much to the effects of the better spatial confinement of the molecules in the ordered mesoporous structure of the host SBA-15.

Spontaneous emission properties of organic film in plane optical microcavity

The spontaneous emission properties of a single layer organic film in plane optical microcavities were studied. Optical microcavity was formed by a Tris(8-quinolinolato) aluminium (Alq) film sandwiched between a distributed Bragg reflector (DBR) and a Ag metallic reflector. Two kinds of microcavities were devised by using a different DBR structure. Compared with a Alq film, significantly spectral narrowing and intensity enhancement was observed in the two microcavities, which is attributed to the microcavity effect. The spectra characteristics of the two microcavities showed that the structure of DBR has much influence on the emission properties of a microcavity. (C) 2000 Elsevier Science S.A. All rights reserved.

Spontaneous assembly of the inclusion complexes of viologen-attached alkanethiols and alpha-, beta-cyclodestrin on gold electrode

Electroactive self-assembled monolayers (SAMs) with well-defined electrochemical responses were prepared by spontaneous assembly of the inclusion complexes (CD/C8VComegaSH) of viologen-attached alkanethiols (C8VComegaSH) and alpha- and beta-cyclodextrin (CD). They were characterized by X-ray photoelectron spectroscopy and cyclic voltammetry. The results demonstrate that the chemisorption process of CD/C8VComegaSH on gold substrate occurs through S-Au bonds, and that the redox sites in SAMs of CD/C8VComegaSH are in a much more uniform environment than those in SAMs of C8VComegaSH.

MEASUREMENT AND CALCULATION OF SPONTANEOUS EMISSION BRANCHING RATIOS, RELATIVE OSCILLATOR-STRENGTHS, TRANSITION-PROBABILITIES AND LEVEL LIFETIMES FOR ATOMIC URANIUM

We propose a laser induced sensitized fluorescence spectrometry for measuring the spontaneous emission branching ratios o?the transitions from the ten levels 5f36d7s7p-7M7, 5f36d7s7p-7L6, 5f37s27p-5K6, 5f26d27s2 - 5L7, 5f46d7s - 7L6, (17,070cm-1)-5L6, 5f26d27s2-5K6, 6d7s7p-7L5, 5f36d7s7p-7K5 and 5f26d27s2-5I5 to the ground state of atomic uranium (UI) for the first time. Their relative oscillator strengths have been measured by means of hollow cathode discharge (HCD) emission spectrometry. The radiative...

MEASUREMENT OF SPONTANEOUS EMISSION BRANCHING RATIOS IN MO(I) TRANSITIONS BY LASER-INDUCED SENSITIZED FLUORESCENCE

I. TNTRODUCTIONThe emission spectroscopic method is usually used to measure spontaneous emission branching ratios. As emission spectra cannot be detected in atomic beams, the laser-induced fluorescence or ion detection method is often used. When the fluorescence method is used to measure branching ratios, it is usually necessary to detect