Two-color Emission Research Articles

2D soot volume fraction imaging in an ethylene diffusion flame by two-color laser-induced incandescence (2C-LII) technique and comparison with results from other optical diagnostics

The two-color laser-induced incandescence (2C-LII) technique can be used for soot volume fraction measurements with no use of a reference flame of known soot concentration. In this work we have exploited the 2C-LII technique with the development of a two-dimensional imaging arrangement. By utilizing an IR pulsed laser, a laser sheet with sharp edges, and controlled fluence, the maximum soot temperature was verified to be around 4000 K in all the investigated regions of an ethylene diffusion flame. The calibration-free 2D 2C-LII arrangement was then feasible and applied for soot imaging. Verification of the soot volume fraction measurements was carried out by comparison with other techniques such as “point” 2C-LII, laser extinction, 2D extinction, and 2D two-color emission techniques. Agreements and some discrepancies are discussed.

2-pyridone: The role of out-of-plane vibrations on the S1↔S spectra and S1 state reactivity

The S(1)<-->S(0) vibronic spectra of supersonic jet-cooled 2-pyridone [pyridin-2-one (2PY)] and its N-H deuterated isotopomer (d-2PY) have been recorded by two-color resonant two-photon ionization, laser-induced fluorescence and emission, and fluorescence depletion spectroscopies. By combining these methods, the B origin of 2PY at 0(0) (0)+98 cm(-1) and the bands at +218 and +252 cm(-1) are identified as overtones of the S(1) state out-of-plane vibrations nu(1) (') and nu(2) ('), as are the analogous bands of d-2PY. Anharmonic double-minimum potentials are derived for the respective out-of-plane coordinates that predict further nu(1) (') and nu(2) (') overtones and combinations, reproducing approximately 80% of the vibronic bands up to 600 cm(-1) above the 0(0) (0) band. The fluorescence spectra excited at the electronic origins and the nu(1) (') and nu(2) (') out-of-plane overtone levels confirm these assignments. The S(1) nonplanar minima and S(1)<--S(0) out-of-plane progressions are in agreement with the determination of nonplanar vibrationally averaged geometries for the 0(0) (0) and 0(0) (0)+98 cm(-1) upper states by Held et al. [J. Chem. Phys. 95, 8732 (1991)]. The fluorescence lifetimes of the S(1) state vibrations show strong mode dependence: Those of the out-of-plane levels decrease rapidly above 200 cm(-1) excess vibrational energy, while the in-plane vibrations nu(5) ('), nu(8) ('), and nu(9) (') have longer lifetimes, although they are above or interspersed with the "dark" out-of-plane states. This is interpreted in terms of an S(1) (') state reaction with a low barrier towards a conical intersection with a prefulvenic geometry. Out-of-plane vibrational states can directly surmount this barrier, whereas in-plane vibrations are much less efficient in this respect. Analysis of the fluorescence spectra allows to identify nine in-plane S(0) (') state fundamentals, overtones of the S(0) state nu(1) (") and nu(2) (") out-of-plane vibrations, and >30 other overtones and combination bands. The B3LYP6-311++G(d,p) calculated anharmonic wave numbers are in very good agreement with the observed fundamentals, overtones, and combinations, with a deviation Delta(rms)=1.3%.

In-flight behaviors of ZrO 2 particle in plasma spraying

In recent years, on-line measurement of particle in-flight behaviors including temperature, velocity and spatial distribution is one of the most important research fields, which can be used to directly analyze the influence of spray parameters and to control the coating quality real-time during plasma spray forming. According to the method of orthogonal experiments, plasma spraying of ZrO 2 has been carried out under different spray parameters in this paper. The particle in-flight behaviors have been measured by a two-color emission technique to analyze the influence of argon flow rate, hydrogen flow rate and electrical current on the particle temperature and velocity. The molten state of the particle has been analyzed. The results showed that the particle velocity increased remarkably with the increase of the argon flow rate. The particle temperature was mainly influenced by the hydrogen flow rate, and increasing electrical current resulted in the increase of the particle temperature and velocity to some extent. The molten state of the particle, affected by the particle in-flight behaviors in the plasma jet, could be used to analyze the deposition efficiency and coating quality.

Fluorobenzene−Nucleobase Interactions: Hydrogen Bonding or π-Stacking?

Studies on modified DNA oligomers and polymerase reactions have previously demonstrated that canonical nucleobases can exhibit stable and even selective pairing with shape-complementary fluorobenzene nucleotides. Because of the fluorination of the pairing edges, hydrogen bonds are believed to be absent, and the local DNA stability has been attributed to pi-stacking and shape complementarity. Using two-color resonant two-photon ionization and fluorescence emission spectroscopies, we show here that supersonically cooled complexes of the nucleobase analogue 2-pyridone with seven substituted fluorobenzenes (1-fluorobenzene, 1,2- and 1,4-difluorobenzene, 1,3,5- and 1,2,3-trifluorobenzene, 1,2,4,5- and 1,2,3,4-tetrafluorobenzene) are hydrogen-bonded and not pi-stacked. The S1 <--> S0 vibronic spectra show intermolecular vibrational frequencies that are characteristic for doubly hydrogen bonded complexes. The bands shift to the blue with increasing hydrogen-bond strength; the measured spectral blue shifts deltanu are in excellent agreement with the ab initio calculated shifts. The spectral shifts are also linearly correlated with the calculated hydrogen-bond dissociation energies D0, published in a companion paper (Frey, J. A.; Leist, R.; Leutwyler, S. J. Phys. Chem. A 2006, 110, 4188). This correlation allows us to reliably estimate the ground-state dissociation energies as D0 approximately 6 kcal/mol of the 2-pyridone.fluorobenzene complexes from the observed spectral shifts.

Matrix Screening of Substituted N-Aryl-1,8-naphthalimides Reveals New Dual Fluorescent Dyes and Unusually Bright Pyridine Derivatives

A 3 x 14 matrix of substituted N-aryl-1,8-naphthalimides was synthesized for the evaluation and discovery of dual fluorescence. Because of their unique photophysical properties, these dual fluorescent systems represent an exception to the widely studied TICT (Twisted Internal Charge Transfer) fluorescent dyes or tautomeric benzofluorescein class of two-color dyes. The matrix library was designed to investigate the effects of heterocycles, particularly pi-excessive and pi-deficient systems. Of the 42 compounds surveyed, five displayed well-resolved two-color emission in solvents as nonpolar as hexane. Based on the observed trends in fluorescence lambda(max) and quantum yield, a new model is proposed that predicts LW and SW emission for these systems. In addition, this model provides potential design features for the synthesis of new dual fluorescent species.

LIEE와 Mie 산란 방법을 이용한 직분식 가솔린 엔진의 스월 및 슬릿 인젝터의 분무 특성

The spray characteristics of DISI injector have a great role in gasoline engine efficiency and emission. Thus, many researchers have studied to investigate the spray characteristics of swirl and slit injectors that are used in a DISI engine. In this study, we tried to provide spray parameters, which affect on the spray characteristics such as injection pressure, ambient pressure and ambient temperature. In addition, we calculated to investigate the break up mechanism of test injectors and obtained to evaluate the spray characteristics. As the ambient pressure increases in case of slit injector, decreases. The laser-induced exciplex fluorescence (LIEF) technique, which is based on spectrally resolved two-color fluorescent emissions, has applied to measure the liquid and vapor phases for on evaporating spray simultaneously. The TMPD/naphthalene proposed by Melton is used as a dophant to detect exciplex signal. The temporal and spatial distribution of liquid and vapor phases during the mixture formation process was measured by this technique. In the LIEF technique, the vapor phase is detected by the monomer fluorescence while the liquid phase is tracked by the exciplex fluorescence. From this experiment, we found that the spray area of the vapor phase is increased with elapsed time after injection and the area of liquid is decreased when the ambient pressure is 0.1MPa. However, the area tends to increase until the end of injection when the ambient pressure is 1.0MPa.

Simulation on simultaneous estimation of non-uniform temperature and soot volume fraction distributions in axisymmetric sooting flames

For visualizing non-uniform absorbing, emitting, non-scattering, axisymmetric sooting flames, because conventional two-color emission methods are no longer suitable, a three-color emission method for the simultaneous estimation of temperature and soot volume fraction distributions in these flames is studied in this paper. The spectral radiation intensities at wavelengths of red, green, and blue, which may be derived from color flame images, are simulated for the inverse analysis. Then the simultaneous estimation is carried out from the spectral radiation intensities by using a Newton-type iteration algorithm and the least-squares method. In this method, a factor is used to balance the wide variation of spectral radiation intensities due to both the wide ranges of temperature and wavelength of the flame radiation. The results indicate that the three-color method is suited for the reconstruction of flame structures with single or double peaks with small difference between the peak and valley. For a double-peaked flame structure with larger peak and valley difference, reasonable result can be obtained just when the mean square deviations of measurement data are small, for example, not more than 0.01.

Luminescence from processible quantum dot-polymer light emitters 1100–1600 nm: Tailoring spectral width and shape

Electroluminescent devices combining two families of PbS colloidal quantum dots to achieve spectrally tailored two-color emission are reported. Depending on device structure selected—the use of two separated layers versus a mixture of nanocrystals—the structures demonstrated light emission either in two infrared frequency peaks corresponding to the spectral region 1.1–1.6 μm or in a wide band spanning this same spectral region. Separated-layer devices exhibit wide tunability in the relative intensity of the two peaks by varying excitation conditions. Replacing oleate with octodecylamine ligands increases the internal electroluminescence efficiency to 3.1%.

Soot pyrometry using modulated absorption/emission

A new method of optical pyrometry for sooting flames has been developed that combines absorption and emission measurements at the same wavelength, reducing the uncertainty in measured soot temperature when compared to commonly used two-color emission pyrometry. The new technique, modulated absorption/emission (MAE) pyrometry, utilizes combined emission and absorption at two wavelengths: 830 and 1300 nm. Large uncertainties in the wavelength-dependent soot refractive index in the infrared are avoided by measuring emissivity directly, eliminating the need to rely on a refractive index model when obtaining temperature. One-color and two-color MAE techniques are validated in this study in a rich laminar premixed ethylene/air flame using diode lasers for transmission measurements. The results show a reduction in the uncertainty of measured temperature in an example case from greater than ±50 K with conventional emission-only pryometry to ±20 K with MAE pyrometry. Advantages of MAE over the conventional method are greatest for soot volume fractions on the order of 10 −7 or greater, typical of laboratory flames used in soot formation and growth studies.

Approximate Two-Color Emission Pyrometry

Abstract Approximate methods for the determination of a temperature field using pure emission pyrometry applied to a two-dimensional nonoptically thin flame without variation along a line of sight are presented. In the absence of an absorption measurement, emission pyrometry depends on theoretical spectral information. Limitations of existing techniques stem from the fact that spectral information is a function of temperature only for the optically thin situation, by and large the situation to which current techniques apply, and temperatures above 1000 K. Through extensive narrow-band calculation using a simulated flame over polymethylmethacrylate, we show that the spectral information contained in the equivalent bandwidth ratio is approximately a constant for the 2.8 μm/1.8 μm band pair and appropriate bandwidths. The constant can be evaluated from emission measurements at a point where the temperature is known or can be estimated using, e.g., the maximum flame temperature of a simulated flame and the peak band intensities. The temperature field evaluated with this approximately constant value of the equivalent bandwidth ratio, Ar, is accurate to within five percent for temperatures down to 450 K. [S0022-1481(00)02601-3]

Two color emission from PPV-PTV copolymer and Alq3 hetero-sturcture EL device

An alternating copolymer of PPV and PTV, poly[2-methoxy-5-(3,7-dimethyl)octyloxy-1,4-phenylenevinylene-alt-2,5thienylenevinylene] (DAPPV-PTV) has been synthesized. Single layer EL device using DAPPV-PTV as an emitting layer between ITO and Al electrodes has been fabricated, and the light emission becomes visible at 3 V. The EL emission maximum of the device is about 620 nm. Double layer EL device using DAPPV-PTV and Alq3 has also been fabricated. The double layer EL device shows two-color emission depending on the applied voltage. The device emits a pale green color from 8 V, and then the color turns to red at about 18 V.

Determination of the Soot Volume Fraction in an Ethylene Diffusion Flame by Multiwavelength Analysis of Soot Radiation

The features of the multiwavelength emission technique for the measurement of soot volume fraction and temperature in an ethylene diffusion flame have been investigated. For this purpose we have exploited the emission spectra from 300 nm to 800 nm and a mathematical Abel inversion procedure. To interpret the measurements, the quantity f v / K abs = λ/(36π F(λ)), here called natural length for absorption, l abs , is modeled as a continuous function according to literature data. Soot temperature profiles were also obtained showing small variations in the investigated region of the flame. Extinction measurements on the same flame were compared, and good agreement was found between the two techniques. With respect to the more-common two-color emission technique, the use of a wide set of spectral data reduces the uncertainties due to the determination of the index of refraction of soot. Different sets of refractive index have been compared and the results are discussed.

Fluorescence cross-correlation: A new concept for polymerase chain reaction

In this article we present a new concept for the detection of any specifically amplified target DNA sequences in multiple polymerase chain reactions (PCR) based on fluorescence correlation spectroscopy (FCS). The accumulation of double-stranded target DNA is monitored by the cross-correlated fluorescence signals provided by two amplification primers which are 5′-tagged with two different kinds of fluorophores (Rhodamine–Green™ and Cy5™). Only the amplified target DNA sequence carrying both primers is observed. Its signal emerges from the background of non-incorporated or non-specifically incorporated primers. Down to 10–25 initial copy numbers of the template in the PCR compartment DNA can presently be detected. No external or internal standards are required for determining the size and the amplified copy number of specific DNA. The PCR amplification process is started with all ingredients in a single compartment (e.g. of a microtiter plate), in which amplification and measurement are performed. This eliminates the need for post-PCR purification steps. The homogeneous one-tube approach does not depend on fluorescence energy transfer between the fluorogenic dyes. Thus, it does not interfere with the enzymatic amplification reaction of PCR and allows the continued use of different conditions for amplifying DNA. The results exemplified by PCR-amplified 217- bp and 389-bp target DNA sequences demonstrate that the analysis based on two-color fluorescence cross-correlation is a powerful method for simplifying the identification of targets in PCR for medical use. For this purpose, an instrument optimized for two-color excitation and detection of two-color emission has been developed, incorporating the principle of confocal arrangement.

Three-color emission of organic electroluminescent device with vapor deposited multilayer structure

Multicolor electroluminescent (EL) device that emits red (R), green (G) and blue (B) lights has been realized by stacking a two-color emission part and a monocolor emission part. The former part consists of red and blue emission layers and an electron blocking layer, which can emit red and blue lights varied by changing the polarity of applied field, whereas the latter part consists of a hole transporting layer and a green emission layer, which can emit green light. The emission color from the R-G-B emission device can be modulated by applying various voltage to the two color part and to the monocolor part, separately.

The metalorganic chemical vapor deposition growth of AlAsSb and InAsSb/lnAs using novel source materials for Infrared Emitters

We have grown AlSb and ALAsxSb1-x epitaxial layers by metalorganic chemical vapor deposition (MOCVD) using trimethylamine or ethyldimethylamine alane, triethylantimony, and arsine. These layers were successfully doped p- or n-type using diethylzinc or tetraethyltin, respectively. We examined the growth of AlAsxSb1-x using temperatures of 500 to 600‡C, pressures of 65 to 630 Torr, V/III ratios of 1-17, and growth rates of 0.3 to 2.7 Μm/h in a horizontal quartz reactor. We have also grown gain-guided, injection lasers using AlAsSb for optical confinement and a strained InAsSb/lnAs multi-quantum well active region using MOCVD. The semi-metal properties of a p-GaAsSb/n-InAs heterojunction are utilized as a source for injection of electrons into the active region of the laser. In pulsed mode, the laser operated up to 210K with an emission wavelength of 3.8-3.9 Μm. The dependence of active region composition on wavelength was determined. We also report on the two-color emission of a light-emitting diode with two different active regions to demonstrate multi-stage operation of these devices.

Cascade Connected Organic El Diodes for Multi-Color Emission

AbstractMulticolor electroluminescent (EL) device which emits red (R), green (G) and blue (B) light has been realized by stacking a two-color emission part and a single-color emission part. The former part consists of two emissive layers of red and blue light, which can be selected by changing the polarity of applied field. The latter part consists of a single emissive layer of green light. The emission color from the R-G-B emission device can be modulated by the combination of applying various voltages to the two-color and to the single-color emission parts, separately.

Environment-sensitive Labels in Multiplex Fluorescence Analyses of Protein-DNA Complexes

Fluorescein is widely used for protein labeling because of its high extinction coefficient and fluorescence emission quantum yield. However, its emission is readily quenched by various pathways. We exploit these properties of fluorescein to examine the self-association of a DNA binding protein and determine the amount of the protein in gel-shifted complexes with specific DNA. A construct (HSFDT385SH) of the heat shock transcription factor (HSF) was expressed that contains the DNA-binding and trimerization domains, residues 192-385 of HSF, with four additional COOH-terminal residues, GMLC, and then labeled at the COOH-terminal cysteine with fluorescein 5-maleimide to form HSFDT385-Fl. The fluorescence increase accompanying the formation of heterotrimers on titration of HSFDT385-Fl with HSFDT385SH) led to an estimate of 3 x 10(-16) M2 for the equilibrium constant for trimerization of HSFDT385SH. HSFDT385-Fl fluorescence also increased 1.7-fold on binding to specific DNA, but not to nonspecific DNA. The protein and DNA content of the several gel-shifted complexes of HSFDT385-Fl (lambdamaxem 532 nm) with specific DNA labeled noncovalently with the energy transfer heterodimer TOTAB (lambdamaxem 658 nm) were accurately determined by a two-color fluorescence emission assay with 488 nm excitation.

Measurements of Time Delays in Superradiant Laser Emssions from Binary Dye Mixtures

The concentration dependence of the time delays, in the range of 80–800 ps, between two-color superradiant laser emissions from three enthanol solutions of the binary dye mixtures, C460/DF, DF/R640, and C460/R640, which were excited using a 1 ns transversely excited atmospheric (TEA) N2 laser was measured by a fast streak camera. While these time delays confirmed that radiative laser energy transfer as the predominant mechanism for multicolor laser emission from a single dye-mixture solution, these emissions were not usually obtained simultaneously, even when a broadband optical resonator was used.

Excited-state proton transfer in gas-phase clusters: 2-Naphthol⋅(NH3)n

Excited-state proton transfer was studied in supersonically cooled neutral acid-base clusters of 2-naphthol⋅(NH3)n with n=1-10, using size-selective two-color resonant two-photon ionization (R2PI) and fluorescence emission techniques. The smaller clusters (n≤3) show vibrationally resolved spectra and do not exhibit excited-state proton transfer. Two rotamers (cis and trans) were observed for each cluster size; these exhibit very different electronic-vibrational couplings to the intermolecular modes, reflecting the orientation of the (NH3)n cluster relative to the electronic transition dipole moment of the aromatic chromophore. Excited-state proton transfer occurs for n≥4, as evidenced by (a) a large spectral red shift (≊8000 cm−1) of the fluorescence emission band; (b) large increase in the emission bandwidth; (c) similarity of the fluorescence band position and width to that of 2-naphtholate anion in neutral or basic aqueous solution. In absorption, the S1←S0 bands are substantially broadened for clusters with n≥4, but are not shifted to the red, as is the case for the analogous 1-naphthol⋅(NH3)n clusters. The cluster-size dependence of the proton transfer reaction is mainly controlled by the cluster proton affinity.

Comparison of Raman and thermocouple temperature measurements in flames

A new method of optical pyrometry for sooting flames has been developed that combines absorption and emission measurements at the same wavelength, reducing the uncertainty in measured soot temperature when compared to commonly used two-color emission pyrometry. The new technique, modulated absorption/emission (MAE) pyrometry, utilizes combined emission and absorption at two wavelengths: 830 and 1300 nm. Large uncertainties in the wavelength-dependent soot refractive index in the infrared are avoided by measuring emissivity directly, eliminating the need to rely on a refractive index model when obtaining temperature. One-color and two-color MAE techniques are validated in this study in a rich laminar premixed ethylene/air flame using diode lasers for transmission measurements. The results show a reduction in the uncertainty of measured temperature in an example case from greater than ±50 K with conventional emission-only pryometry to ±20 K with MAE pyrometry. Advantages of MAE over the conventional method are greatest for soot volume fractions on the order of 10−7 or greater, typical of laboratory flames used in soot formation and growth studies.