Influence of scattering on superluminescence in composites dye solution – nanoparticles

Spectral and energy luminescence characteristics of R6G dye solutions in ethanol with addition of Ag nanoparticle suspensions in different aggregate states are experimentally investigated. It is demonstrated that incorporation of non-aggregated and aggregated nanoparticles causes the superluminescence thresholds in R6G solutions to decrease. It is established that the optical properties of the laser beam propagation channel are transformed when low-power (20 mW) cw laser radiation passes through the suspension of nanoparticles. This is manifested through the occurrence of a region with enhanced nanoparticle density in the laser beam center, on which diffraction of laser radiation is observed.     

Spectral and temporal characteristics of fluorescence of drops comprising dissolved dye excited by the IR laser radiation

Fluorescence of solutions of rhodamine 6G in the form of single drops of millimeter sizes excited by the intense IR and visible laser radiation (with duration of laser pulses of ∼10 ns and wavelengths of 1064 and 532 nm) is experimentally investigated. It was found that the power thresholds of fluorescence excitation for drops comprising the dissolved dye are, by an order of magnitude, less than for a cell with dissolved dye. The dichromatic drop fluorescence has been revealed, which is manifested through the occurrence of two maxima in the fluorescence spectrum of drops comprising dissolved rhodamine 6G. The first maximum coincides with that of the dye fluorescence spectrum, while the second maximum is shifted by ∼1000 cm⁻¹ and is on the slope of the fluorescence line profile. It is shown that the duration of drop fluorescence does not exceed the duration of the exciting pulse.     

Optically excited secondary emission spectra of photonic crystals based on synthetic opals

The photonic dispersion, the group-velocity dispersion, the effective mass, refractive index, and the spectral distribution of the density of photonic states near the edge of the photonic stop band are numerically calculated in the one-dimensional model for photonic crystals based on synthetic opals. The fluorescence spectra of rhodamine 6G and 2,5-bis(2-benzoxazolyl)hydroquinone molecules infiltrated into a synthetic opal are measured. For both substances, it is observed that the spontaneous emission intensity in the range of the photonic stop band is appreciably suppressed. A blue shift of the fluorescence spectrum of rhodamine 6G molecules is revealed. Secondary emission of synthetic opals infiltrated with colloidal silver is observed in the Stokes range under excitation of opals by radiation at λ = 400 nm. The spectrum of the secondary emission is located in the range 450–590 nm, which contains the stop band and intervals near its edges.     

S0-S n two-photon absorption dynamics of rhodamine dyes

The intensity-dependent transmission of picosecond ruby laser pulses of different duration through methanolic and ethanolic solutions of rhodamine B and rhodamine 6G is analysed. The transmission is affected by S₀-S _n two-photon absorption, by stimulated emission at the pump-laser frequency, by amplified spontaneous emission and by excited-state absorption. Various parameters involving the two-photon absorption dynamics are determined by comparing experiments with numerical simulations.     

Remote Detection of Asymmetric Dimethylhydrazine in the Atmosphere

The possibility of remote atmospheric detection of an ecotoxicant (asymmetric dimethylhydrazine) by means of a fluorescing mark is considered. The effect of asymmetric dimethylhydrazine on the spectral-luminescent properties of rhodamine 6G, nonsubstituted rhodamine, and amino- and hydroxysubstituted derivative of phenalenone is studied. It is shown that the molecules containing amino groups change their spectral properties and lose emitting properties in the presence of dimethylhydrazine. The hydroxysubstituted derivative of phenalenone in dimethylhydrazine generates laser radiation when pumped by a Nd:YAG-laser and shows the stimulated fluorescence effect in aerosols.     

Laser-Induced Silver Nanoparticles Deposited on Optical Fiber Core for Surface-Enhanced Raman Scattering

We report on surface-enhanced Raman scattering （SERS） probes based on silver nanopaxtieles which axe deposited on the core of the distal end of standard single mode fibers, by means of the very simple, versatile, and lowcost laser-induced nanoparticle technique. The morphological features of the Ag nanoparticles vary according to the experimental conditions such as laser power, illumination time, and concentration of the reaction solution. The SERS activity of the probes is demonstrated with the detections of rhodamine 6G aqueous solutions. The detections are made from both ends of the probes, i.e., in direct detection mode from the end with nanoparticles and in remote detection mode from the distal end, respectively.     

Specific Features of XeCl*-Laser Radiation Absorption by Concentrated Solutions of Organic Dyes

The transmission of focused laser radiation with power densities in the range (1–250) MW/cm² through solutions of laser dyes (substituted paraterphenyls and rhodamine 6G) is investigated. The dependence of the transmission on the exciting radiation power density is measured, and numerical modeling is used to estimate the lifetime of the fluorescent state of molecules and the influence of stimulated emission on the lifetime of the S ₁ state. The effect of scattering on the transmission of highly absorbing media is demonstrated under nanosecond excitation.     

Spectroscopic and Laser Studies of Mixed Rhodamine 6G and 10-Phenyl-9-acetoxyanthracene Solutions

The spectroscopic and laser parameters of a mixed donor (10-phenyl-9-acetoxyanthracene derivations)-acceptor (rhodamine 6G) solutions have been determined. The studies performed show that rhodamine 6G is responsible for the lasting of the mixed solution. The 10-phenyl-9-acetoxyanthracene added to the R6G lasing solution decreases the spectral range of lasing and the gain value, G(), of the solution. These changes in the lasing parameters are caused by electron energy transfer processes of different types. The results of fluorescence studies of the mixed donor-acceptor solutions point out that the long-range dipole-dipole interaction mechanism of the static quenching accompanied by the formation of nonemitting complexes in the dye mixture is responsible for the noted lasing and fluorescence changes.     

银溶胶的合成、表征及其表面增强拉曼散射特性研究

报道了一种简单的合成均匀、稳定的银溶胶的方法,通过透射电子显微镜(TEM)观察其形貌,并利用UV-Vis谱、XPS等手段对其进行表征,以罗丹明6G(R6G)作为探针分子研究在银溶胶纳米粒子上的表面增强拉曼效果,结果表明所合成的银溶胶具有较强的表面增强拉曼散射效果。     

Particular features of manifestation of energy migration toward impurity in nanoparticles of metal complexes

We measure the fluorescence quantum yields (q _fl) of complexes of Al, Sc, Y, In, Lu, and Gd with dibenzoylmethane in aqueous and isopropanol solutions at different concentration ratios of ions and dike-tone. We reveal that, for the examined solutions, qfl of complexes varies more than by two orders of magnitude under the influence of the heavy atom. It is found that a considerable decrease in q _fl and τ_fl of ligands of complexes of listed ions caused by the influence of heavy atoms weakly affects the intensity of sensitized fluorescence of Nile red and rhodamine 6G molecules introduced into nanoparticles from these complexes in aqueous solutions. The revealed result is explained by the comparability of the singlet exciton free path length and the dimension of nanoparticles under study. We show that a lower fluorescence intensity of heavy metal complexes makes it possible to decrease its contribution in the range of the cofluorescence maximum of rhodamine 6G and to monitor the occurrence of the dye in the aqueous solution down to the concentration of 0.05 nM. We show that, in nanoparticles from Eu complexes, further fluorescence quenching of dibenzoylmethane is observed, as well as the appearance of cofluorescence of rhodamine 6G, the intensity of which is comparable with its intensity in nanoparticles of other complexes. The appearance of this cofluorescence cannot be explained by the existence of S-S energy migration.     

Photophysical and laser characteristics of pyrromethene 567 dye: Experimental and theoretical studies

Narrow-band laser performance of alcohol solutions of pyrromethene 567 (PM567) and rhodamine 6G (RH6G) dye was investigated using a home-made GIG-configured dye laser, excited by the second-harmonic radiation (at 532 nm) of a pulsed Nd:YAG laser. Higher laser efficiency was observed with PM567 dye (∼23% peak) in comparison to the commonly used RH6G dye (16.5%), in spite of much lower fluorescence quantum efficiency of the PM567 (0.83) vis-à-vis RH6G (0.98) dye solutions in ethanol. First principle-based electronic structure calculations were performed on PM567 dye in the ground (S ₀) and excited states (S ₁) using density functional theory to elucidate the structure and photophysical properties of the dye.     

Nonlinear luminescence of high-concentration rhodamine solutions: On the problem of pulsed laser cooling

The conditions of occurrence of collective photoinduced luminescence in model solutions are determined. The transmittance and luminescence of concentrated solutions of rhodamine 101 under excitation by laser pulses in the Stokes and anti-Stokes spectral ranges are studied. It is shown that, at high pump energies, collective photoinduced luminescence, which competes with induced radiation, plays a significant role in luminescence generation. Temperatures of heating and cooling of solutions are estimated. The photodynamics of cooling of solutions of complex molecules under their pulsed (Stokes and anti-Stokes) excitation is analyzed.     

Photoluminescence of aromatic compounds in photon traps under resonant pulse-periodic excitation

The photoluminescence spectra of aromatic compounds in a photon trap under ultraviolet pulse-periodic excitation are recorded. It is shown that the photoluminescence spectrum shape depends on the material layer thickness in a cell, physical state of the sample, and exciting radiation characteristics: as the layer thicknesses decreases, the intensity is significantly redistributed, which is explained by the transition from spontaneous luminescence to superluminescence.     

Experimental and theoretical evidence for the chemical mechanism in SERRS of rhodamine 6G adsorbed on colloidal silver excited at 1064 nm

The evidence for the existence of a chemical mechanism in surface‐enhanced resonance Raman scattering (SERRS) of rhodamine 6G (R6G) adsorbed on colloidal silver excited at 1064 nm is reported on the basis of experimental and theoretical analyses. A weak absorption peak at around 1060 nm for R6G‐functionalized silver nanoparticles was observed, which is not present in the individual spectra of R6G or silver nanoparticles. Theoretically, the charge difference density reveals that this weak absorption is a metal‐to‐molecule charge transfer excited state. Copyright © 2010 John Wiley & Sons, Ltd.     

纳米银粒子对表面吸附罗丹明B的光谱学性质的影响及电解质效应研究

基于贵金属纳米粒子的局域场增强效应,利用透射电子显微镜、紫外-可见分光光度计和荧光分光光度计等分析手段研究了纳米银粒子对表面吸附罗丹明B的光谱学性质的影响以及罗丹明B-纳米银体系中加入电解质离子后,电解质离子与纳米银、染料分子间的相互关系和作用.研究结果表明,当罗丹明B溶液的浓度小于0.6 μmol·L－1时,微量纳米银可使其荧光强度略增加,继续增加纳米银浓度则造成荧光强度下降.当罗丹明B溶液的浓度高于0.6 μmol·L－1时,纳米银总是引起溶液的荧光强度下降.KNO3、KCl、Ca(NO3)2、MgCl2和CaCl2电解质可造成纳米银粒子不同程度的聚集和生长.引起的纳米银粒子的聚集程度关系为:CaCl2>MgCl2>KCl>Ca(NO3)2>KNO3.随着电解质加入量的增加,溶液的荧光强度先下降,而后又逐渐增强,直至达到定值.各电解质对罗丹明B-Ag溶液的荧光强度影响强弱关系为Ca(NO3)2>CaCl2>MgCl2>Cl>KNO3.     

Laser-induced photoprocesses in solutions and films of the CdSe/ZnS nanoparticles

The photophysical properties of solutions and films with relatively high concentrations of CdSe/ZnS nanoparticles are studied in the presence of the visible laser irradiation in a wide range of power densities. The short-wavelength wing detected in the photoluminescence spectra of the solutions of quantum dots is due to the selective laser excitation of small-size nanoparticles. A comprehensive analysis of the anti-Stokes photoluminescence of the nanoparticles in solutions and films indicates the thermal mechanism of this phenomenon. The dimensional quantization effect, narrow spectra, and a relatively high luminescence yield are retained in the films with a high nanoparticle concentration. The luminescence spectra of the films remain unchanged when the laser flux density increases to 1 × 10⁶ W/cm². The effect of the laser radiation on the nanoparticle films is studied at the flux densities exceeding the damage threshold (5 × 10⁶–1 × 10⁹ W/cm²).     

Sensitization of fluorescence of dye molecules in nanoparticles of metal complexes

We studied the dependence of absorption and fluorescence spectra of complexes of Al, In, Sc, Y, and La with dibenzoylmethane and naphthoyltrifluoroacetone, as well as the dependence of sensitized fluorescence of dyes in nanoparticles of these complexes, in relation to the water pH, the ratio between ions and diketones, and the ion selection. We showed that the ability of complexes of ions to form nanoparticles that efficiently sensitize dye molecules incorporated into them is determined by stability constants of these ions with organic ligands and by their ability to compete with the formation of hydroxy complexes of these ions. We found that nanoparticles consist of diketonates of different compositions and that Nile red incorporated into nanoparticles is an indicator of the dependence of the composition of nanoparticles on the selection of the central ion of complexes and conditions of their formation. We revealed that complexes M(diketone)(OH)₂ self-assemble into nanoparticles with an admixture of dye molecules and efficiently sensitize dyes upon excitation into absorption bands of complexes. We showed that, at concentrations of rhodamine 6G in water smaller than 50 nM, the use of a solution that contains 50 μM of Al(III), In(III), or Sc(III) + 50 μM of naphthoyltrifluoroacetone makes it possible to increase the sensitivity of the luminescence analysis by 20-fold for the presence of rhodamine 6G in an aqueous solution.     

Comparative laser performances of pyrromethene 567 and rhodamine 6G dyes in copper vapour laser pumped dye lasers

Narrowband laser performances and photochemical stability of alcoholic solutions of pyrromethene 567 and rhodamine 6G dyes, under high-repetition rate copper vapour laser (at 510 nm), as well as, high-peak intensity Nd:YAG laser (at 532 nm) excitation have been investigated. We have observed that pyrromethene 567 dye solutions offer higher efficiency, wider tuning range, but lower photochemical stability and higher lasing threshold than that of rhodamine 6G dye solutions. An addition of about 100 mM DABCO, as a singlet oxygen quencher, in pyrromethene 567 dye solutions improved its photochemical stability close to that of rhodamine 6G. The observation of higher slope efficiency, in spite of higher threshold pump energy for pyrromethene 567 dye than that of rhodamine 6G dye solutions, was explained by a predictive model on gain characteristics of both dye solutions as a function of pump energy. PACS 42.55.Mv; 42.55.Rz; 42.70.Hj; 42.70.Jk     

Surface-enhanced Raman scattering from silver nanostructures with different morphologies

Scanning electron microscopy and X-ray diffraction reveal that four different types of crystalline silver nanostructures including nanoparticles, nanowires, nanocubes, and bipyramids are synthesized by a solvothermal method by reducing silver nitrate with ethylene glycol using poly(vinylpyrrolidone) as an adsorption agent and adding different quantities of sodium chloride to the solution. These nanostructures which exhibit different surface plasma resonance properties in the ultraviolet–visible region are shown to be good surface-enhanced Raman scattering (SERS) substrates using rhodamine 6G molecules. Our results demonstrate that the silver nanocubes, bipyramids with sharp corners and edges, and aggregated silver nanoparticles possess better SERS properties than the silver nanowires, indicating that they can serve as high-sensitivity substrates in SERS-based measurements.     

环己烷/水界面自组装纳米银膜及性能研究

在环己烷/水界面以自组装的方式将单层密排的银纳米粒子膜转移到亲水性的硅片上,以罗丹明6G(R6G)为探针分子,通过与直接滴加银胶溶液和混合R6G后的银胶溶液得到的两种SERS基底对比,密排银纳米粒子膜展现了极高的灵敏度(R6G的检测极限为10-9 mol/L)和信号再现性。结合有限时域差分法(FDTD)对其增强原因进行了模拟分析,实验结果与理论模拟基本相符。