Luminescence properties of rhodamine 6G intercalated in surfactant/clay hybrid thin solid films

To develop the solid-state laser oscillator based on laser dye compounds, the incorporation of rhodamine 6G (R6G, a laser dye) in cetyltrimethylammonium (CTA+) cationic surfactant/montmorillonite clay hybrid (HpC) thin solid films was investigated. The R6G/HpC samples were prepared by immersing the HpC films into a R6G aqueous solution with various concentration. X-ray diffraction patterns of the films of HpC, measured before and after the intercalation of R6G, proved the coexistence of both the dye and surfactant in clay interlayer spaces. All prepared thin films exhibited luminescence. It indicates that CTA+ molecules play a role as a partial suppressor of the aggregation of R6G molecules which prevents fluorescence. Moreover, the luminescence property of the present thin films was observed to be dependent on the co-intercalated degree of R6G molecules, indicating that the R6G intercalating in HpC interlayer space molecules exist as two or more luminescence species in the clay interlayer space.     

Characterization of supported solid thin films of Laponite clay. Intercalation of rhodamine 6G laser dye

The morphology of thin films of Laponite (Lap) clay elaborated by the evaporation method and spin-coating technique was analyzed by atomic force microscopy and scanning electron microscopy, indicating a better quality film for the latter procedure. Rhodamine 6G (R6G) laser dye was intercalated into these films by ion exchange mechanism, performed by immersing the clay film into adequate dye solutions in which the effect of the dye concentration, immersion time, and nature of the solvent on the adsorption process were checked. The adsorption of R6G at the interlayer space of Lap was analyzed by the X-ray diffraction technique, and the presence of several R6G species (monomers and aggregates) was characterized by absorption and fluorescence spectroscopies. Less viscous solvents lead to higher dye loadings, suggesting a diffusional process for the intercalation of the dye in the interlayer spaces of Lap, and polar solvents favor the swellability of the interlayer space giving rise to a more homogeneous distribution of R6G molecules through the film and decreasing the dye aggregation. With the aging of the samples, the dye molecules can migrate through the interlayer spaces, leading to a more expanded distribution of R6G molecules and to the dye deaggregation.     

罗丹明6G的荧光光谱

在苯-甲醇混合溶剂中测量了罗丹明6G的吸收光谱和荧光光谱,发现体系中荧光强度和光密度随甲醇浓度的增长而增长.这可解释为甲醇浓度增加,溶液的介电常数也增加,这样自由离子浓度增加,未解离分子浓度减少.结果表明无论由吸收光谱和由荧光光谱都说明荧光来源于R6G离子.     

Photoresponse and anisotropy of rhodamine dye intercalated in ordered clay layered films

In order to elaborate organized two-dimensional arrangements of fluorescent dyes in host solid layered materials, rhodamine 6G (R6G) is encapsulated in supported thin films of laponite (Lap) clay. Clay films are elaborated by the spin-coating technique and their surface morphology is analyzed by scanning electron (SEM) and atomic force (AFM) microscopies. The internal order of the stacked clay layers is checked by X-ray diffraction technique (DRX). The thermostability of R6G in the Lap films is discussed on the basis of several thermogravimetric and calorimetric techniques (TG, DTA and DSC). The R6G adsorbed species in Lap films are characterized by absorption and fluorescence (steady-state and time-resolved) spectroscopies. Monomers, dimers and higher-order aggregates are identified for very low (<0.1%), moderate (1–25%) and high (>40% of the total cation exchange capacity, CEC, of the clay) dye content, respectively. Both non-fluorescence H-type and fluorescent J-type aggregates of R6G in Lap films are characterized.Absorption and fluorescence techniques with linearly polarized light are applied to evaluate the anisotropic photoresponse of R6G in Lap films, from which the preferential orientation of dye molecules with respect to the clay layers can be evaluated. The validity of the newly established fluorescence polarization is contrasted with the well-established absorption polarization method, and the emission spectroscopy with linearly polarized light can be applied to establish the preferential orientation of fluorophore molecular probes incorporated in any rigid and ordered 2D host materials, including monolayers and biological membranes.     

Fluorescent plasma nanocomposite thin films containing nonaggregated rhodamine 6G laser dye molecules

This letter reports a novel methodology for the synthesis of dye-containing nanocomposite thin films containing fluorescent rhodamine 6G (Rh6G) laser dye molecules. The nanocomposites are deposited in one step at room temperature in a downstream microwave plasma operating at low pressure and power. By controlling the plasma chemistry, it is possible to reduce the formation of dye dimers and higher aggregates that quench the fluorescence of the dye molecules. The films are intensely absorbent and fluorescent, insoluble in water, mechanically stable, and present good adhesion to the substrate. Besides, the method is compatible with the present silicon technology and therefore particularly interesting for the fabrication of integrated optoelectronic devices.     

Aggregation states of rhodamine 6G in electrospun nanofibrous films

Novel fluorescent composite nanofibrous films of rhodamine 6G (Rh6G) and polyacrylonitrile (PAN) are first prepared by electrospinning. The aggregation states of Rh6G in electruspun nanofibrous films are studied as a function of concentrations and characterized by UV–vis absorption spectroscopy and emission and excitation fluorescence spectroscopy. We have also used casting films as reference material to compare the effect of incorporation of Rh6G in electrospun nanofibrous films and casting films. The large specific surface area of the nanofibers and fast evaporation of the solvents in the electrospinning process reduced the aggregation of Rh6G. The appearance of fluorescent J-type dimers, even at higher dye concentration in elctrospun films, demonstrates that the electrospun films are an ideal material for incorporation of fluorescent dyes.     

The study of the photophysics and primary photochemistry of rhodamine 6G aggregates

The decay processes of the excited singlet and triplet states of rhodamine 6G aggregates were investigated. It was shown that aggregation results in a substantial increase of the quantum yield of intersystem crossing. The triplettriplet (TT) absorption spectra of rhodamine 6G aggregates were measured. The decay kinetics of the triplet state of dye aggregates were studied. It was shown that the main pathways of triplet state deactivation are unimolecular decay and TT interaction. A correlation between the values of the rate constants of unimolecular triplet state decay and of some properties of the solvents is discussed. The mechanism of electron transfer in photoreactions of rhodamine 6G aggregates was considered. It was shown that electron transfer occurs via the triplet state of aggregates by TT interactions and reactions with electron donors and acceptors. The ability of the triplet state of rhodamine 6G aggregates to sensitize redox reactions was established. Spectra of ion radical species and the values of rate constants for some elementary steps were determined.     

Absorption and fluorescence spectroscopy of rhodamine 6G in titanium dioxide nanocomposites

A comparison has been made between the spectroscopic properties of the laser dye rhodamine 6G (R6G) in mesostructured titanium dioxide (TiO(2)) and in ethanol. Steady-state excitation and emission techniques have been used to probe the dye-matrix interactions. We show that the TiO(2)-nanocomposite studied is a good host for R6G, as it allows high dye concentrations, while keeping dye molecules isolated, and preventing aggregation. Our findings have important implications in the context of solid state dye-lasers and microphotonic device applications.     

Adsorption of fluorescent R6G dye into organophilic C12TMA laponite films

The absorption and fluorescence properties of rhodamine 6G (R6G) in organophilic laponite (Lap) clay films are studied. For this purpose, organo-Lap clays are synthesized by the incorporation of dodecyltrimethylammonium (C12TMA) as surfactant into the interlayer space of Lap clays. Two organo-Lap clays are prepared: one with moderate surfactant content (around 70% of the total cation-exchange capacity (CEC) of the clay) and a second with a high surfactant loading (about 130% CEC). Supported films are elaborated by the spin-coating technique and characterized by several techniques such as atomic force microscopy, elemental CHN analysis, X-ray diffraction, and thermogravimetry. IR spectroscopy reveals that the intercalation of R6G into organo-Lap films takes place at the detriment of the adsorbed C12TMA molecules. The photophysical properties of R6G monomers in the interlayer space of Lap films are improved by the presence of surfactant molecules. Moreover, organophilic environments can reduce the dye aggregation and favor the formation of fluorescent J-type aggregates, enhancing the fluorescence ability of dye/clay films with high dye contents. This improvement depends on the surfactant content.     

Analysis of thin solid films and surfaces by infrared spectroscopy

Thin solid films and surfaces are characterized by IR spectroscopy, based on reflectance and transmittance measurements, in particular with polarized light at oblique incidence. Thus two independent data sets fors- andp-polarization are available. Atp-polarization additional absorption lines at the zeros of the dielectric function are observed (Berreman-mode). The interpretation of the measured spectra is carried out by a fit procedure to simulate the observed spectra. As a result the specimens are characterized in terms of vibronic resonances and their oscillator strengths or concentration, thicknesses of various films in a stack of layers, profiles of depth depending chemical composition, or concentration and mobility of conduction electrons.All examples are relevant for application in technology, as microelectronics, thin film technology, catalysis, e.g. The results of the IR analysis are compared with those of other analytical methods as SIMS, RBS, and AES. The agreement is very good. One important advantage of the IR analysis, however, is the fact that it is a non-destructive method.     

Characterization of thin metastable vanadium oxide films by Raman spectroscopy

Thin films are potentiodynamically generated on vanadium in Ba²⁺/acetate electrolyte systems at high voltages. The influence of the anodic potential up to 400 V on the composition and structure of the about 500 nm thin anodic conversion films are investigated. Raman spectroscopy indicates that different film types depend on the electrochemical process parameters. The relationship between the Raman laser excitation power and the amorphous or microcrystalline film structure is also discussed. Beside metastable disordered structures the films contain crystalline phases of V₂O₅, V₄O₉ and barium vanadate, respectively. Received: 15 July 1997 / Revised: 16 February 1998 / Accepted: 21 February 1998     

Characterization of thin metastable vanadium oxide films by Raman spectroscopy

Thin films are potentiodynamically generated on vanadium in Ba²⁺/acetate electrolyte systems at high voltages. The influence of the anodic potential up to 400 V on the composition and structure of the about 500 nm thin anodic conversion films are investigated. Raman spectroscopy indicates that different film types depend on the electrochemical process parameters. The relationship between the Raman laser excitation power and the amorphous or microcrystalline film structure is also discussed. Beside metastable disordered structures the films contain crystalline phases of V₂O₅, V₄O₉ and barium vanadate, respectively.     

Interaction of phospholipids with rhodamine 6G in toluene.

Upon interaction of various glycerophospholipids with Rhodamine 6G in toluene, a typical difference spectrum with an absorption maximum at approximately 515 nm is obtained . This spectrum is obtained with phosphatidylcholine only after treatment with NaCl, which presumably weakens intra- and/or inter-molecular electrostatic binding between the negatively charged phosphate moiety and the protonated nitrogen in this molecule. Absorption at 515 nm was linear for all of the phospholipids investigated from a concentration of approximately 1.2 microM up to at least 50 microM. The highest extinction coefficient was obtained for diphosphatidylglycerol (251 mM-1 cm-1) and all of the compounds tested, with the exception of phosphatidylethanolamine, demonstrated extinction coefficients higher than that of palmitic acid. Thus, the absorption spectrum which results from the interaction of purified glycerophospholipids with Rhodamine 6G in organic solvent is a sensitive measure of the amount of phospholipid present.     

Spectral properties of TMPyP intercalated in thin films of layered silicates

The objective of this study was to investigate the spectral characteristics of tetracationic porphyrin dye (TMPyP), intercalated into films of three smectites. The smectites represented the specimens of high (Fluorohectorite; FHT), medium (Kunipia F montmorillonite; KF), and low layer charge (Laponite; LAP). Intercalation of TMPyP molecules was proven by XRD measurements. The molecular orientations of the dye cations were studied by means of linearly polarized ultraviolet-visible (UV-vis) and infrared (IR) spectroscopies. Both the UV-vis and the IR spectroscopy proved the anisotropic character of the films. The spectral analysis of the polarized UV-vis spectra and consequent calculations of tilting angles of the transition moments in the region of Soret band transitions were in the range of 25-35 degrees . The determined angles indicated that the molecular orientation of the dye cations was almost parallel to the surface of the silicates. Slightly higher values, determined for a FHT film, indicated either a slightly more tilted orientation of the dye cations or the change of molecular conformation after the intercalation of the dye. Quenching of TMPyP fluorescence was observed, resulting from the formation of bimolecular layer arrangements with sandwich-type assemblies of the dye molecules.     

Characterization of metal oxide surfaces and thin semiconductor films by inelastic electron tunneling spectroscopy.

Inelastic electron tunneling spectroscopy (IETS) is a unique surface and interface analytical technique using electron tunneling through a metal/insulator/metal tunneling junction at cryogenic temperatures. It gives the vibrational spectrum of a very thin (nm) insulator film and the adsorbed species on it. The high sensitivity, good resolution, and wide spectral range inherent in IETS enable us to analyze the surface and interface of the insulator in detail. The tunneling junction is a good model system for oxide catalysts, electronic devises, and solid state sensors. Information about the surfaces of alumina and magnesia, the adsorption states and chemical reactions of adsorbed species occurring on these oxides can be obtained through an analysis of the tunneling spectra. The structures and properties of evaporated thin semiconductor films can also be studied. In this review, the surface characterization of alumina and magnesia, the adsorption and surface reactions of organic acids, esters, amides, and nitryls on these oxides, and the characterization of thin evaporated films of Si, Ge, and the oxides are summarized.     

Spectroscopic studies of rhodamine 6G dispersed in polymethylcyanoacrylate

We report here electronic absorption, fluorescence and resonance Raman studies of rhodamine 6G laser dye dispersed in the polymethylcyanoacrylate matrix. In the electronic absorption and fluorescence spectra of dispersed rhodamine 6G, band maxima are red shifted compared to solution. Raman spectra show some new bands. These spectral changes arise due to matrix effect and interaction between rhodamine 6G and the host material involving amine group of rhodamine.     

DFT vibrational calculations of rhodamine 6G adsorbed on silver: analysis of tip-enhanced Raman spectroscopy

The tip-enhanced near-field Raman (TERS) bands of Rhodamine 6G (R6G), that we reported earlier [Chem. Phys. Lett. 2001, 335, 369.], are assigned on the basis of density-functional theory (DFT) calculations at the 6-311++G(d,p) level. The Raman and infrared intensities as well as frequencies of the vibrational modes are used for band assignments. These vibrational modes, in combination with characterization of resonant electronic transitions using time-dependent DFT calculations, predict spectral changes in resonant Raman and surface-enhanced resonant Raman scatterings of R6G. Moreover, the TERS spectra of R6G are analyzed in detail, where interactions between the tip and R6G molecules and their enhancement mechanisms are discussed. Finally, we propose a novel Raman spectroscopy technique capable of detecting molecular vibrations at sub-nanometer scale.     

Characterization of iron-silicon thin films by means of electron diffraction and X-ray spectroscopy

Iron-silicon thin films have been characterized by means of analytical transmission electron microscopic methods. Under certain conditions — composition and annealing temperature — these films exhibit thermoelectric behavior. In particular, the morphology and phase formation which results from annealing of these films, and doping with oxygen and nitrogen, are of interest. The thermoelectric phase -FeSi₂ is formed at temperatures above 500°C. This phase is transformed into electrically conducting phases at about 1000°C. A small oxygen content does not influence this crystallization process. If the oxygen content is higher than 15 atom-% the electrically conducting phases exist even at 500°C. The presence of a small nitrogen content inhibits the formation of the -FeSi₂ phase. The development of silicon and iron nitrides is possible.     

Characterization of ultra‐thin polymer films by polarization modulation FTIR spectroscopy

Self assembly monolayers of octadecyltrichlorosilane Cl₃‐Si‐(CH₂)₁₇‐CH₃ and 17‐cyanopentadecyltrichlorosilane Cl₃‐Si‐(CH₂)₁₇‐CN on silicon wafers have been prepared by adsorption from solution. The molecular orientation within the monolayers was investigated by using Polarisation Modulation FTIR spectroscopy. Quantitative analysis reveals that both types of silanes – monofunctionalised and bifunctionalised – form highly ordered monolayers. A high degree of ordering as well as a small tilt angel of the molecular backbones with respect to the surface normal are indicated by the strength of the Si‐O‐Si stretching modes and the weakness of the CH₂ stretching modes. The decomposition of the terminal nitrile group of the substituted silane into a carboxyl group could be identified. The decomposition is caused by a high local HCl concentration, which develops upon binding of 17‐cyanopentadecyltrichlorosilane to the OH groups of the silicon surface.     

Modeling disorder in polymer aggregates: the optical spectroscopy of regioregular poly(3-hexylthiophene) thin films

Absorption and emission in polymer aggregates is studied theoretically, taking into account excitonic (intermolecular) coupling, exciton-phonon (EP) coupling, and disorder, all treated on equal footing within a generalized Holstein Hamiltonian with numerically generated eigenmodes and energies. The disorder is modeled as a Gaussian distribution of molecular transition frequency offsets of width sigma and spatial correlation length l(0). Both herringbone (HB) and lamellar aggregate morphologies are considered. The emission spectral line shape is shown to undergo marked changes in response to increasing disorder, with the intensity of the ac-polarized 0-0 emission peak generally increasing relative to the replica intensities (0-1,0-2,[ellipsis (horizontal)]) as sigma increases and/or as l(0) decreases. This is contrary to the behavior of the b-polarized component of the 0-0 intensity, which, in HB aggregates, decreases with increasing disorder. Comparisons are made to analogous trends in oligomer aggregates. Analytical results are obtained in the strong EP coupling regime appropriate for conjugated polymers while treating the disorder perturbatively. A method for uniquely determining sigma and l(0) from the emission and absorption spectra is presented. Applications are made to absorption and low-temperature emission in thin films of regioregular poly(3-hexylthiophene), with excellent agreement between theory and experiment obtained for a spatial correlation length of only 3-4 molecules.