Energy transfer and excited state lifetime of some anthracene laser dyes

The lifetimes of some anthrathene derivatives in different solvents have been determined using the phase modulation method. The lifetime of 10-phenyl-2-methyl-9-acetoxyanthracene and 10-(4-acetoxyphenyl)-2-methyl-9-acetoxyanthracene were found to equal 11 and 11 ns in methanol, respectively. Energy transfer from 10-phenyl-2-methyl-9-acetoxyanthracene and 10-(4-acetoxyphenyl)-2-methyl-9-acetoxyanthracene to rhodamine B and rhodamine 110 in different solvents has been studied by using steady-state emission measurements. The large values of the critical transfer distance R₀ and the rate constant of energy transfer k_ET suggest that the mechanism is long-range dipole–dipole energy transfer as described by Förster.     

Observation of laser-induced off-resonance intermolecular electronic energy transfer

We report the observation of off-resonance electronic energy transfer from an excited rhodamine 6G molecule to an azulene molecule in solution. The process requires the coupling of the radiation field in the transfer process. We demonstrate that the relation Y _A I ^1/2 between the acceptor's induced fluorescence intensity and the laser intensity, predicted by Jortner et al. is observed.     

Collective spontaneous emission of dye molecules and lasing

The threshold pump power density for lasing in dye solutions is found to depend on the photon energy of pumping radiation. An increase in the pumping photon energy can significantly lower the threshold pump power of dye lasers. For an ethanol solution of rhodamine 6G with a concentration of 4×10¹⁸ cm^?3, the threshold power density for pumping radiation with a wavelength of 532 nm is 20-fold higher than for pumping radiation with a wavelength of 347 nm. This phenomenon is associated with the competition of collective spontaneous emission, which can lead to the efficient deactivation of excited molecules in femtosecond times, and the dephasing of excited molecules due to the intramolecular nonradiative processes of absorbed-energy conversion. An increase in the dephasing rate with the increasing energy of exciting photons lowers the efficiency of collective spontaneous emission and increases the concentration of dephased excited molecules responsible for lasing.     

Fluorescence resonance energy transfer between acridine orange and rhodamine 6G and analytical application in micelles of dodecyl benzene sodium sulfonate

A new method for the determination of erythromycin by energy transfer fluorescence quenching of acridine orange (AO)—rhodamine 6G (R6G) in micelles solution studied and established. It was found that the effective energy transfer could occur between AO and R6G in the dodecyl benzene sodium sulfonate at and Britton-Robinson buffer (BR, pH=5.72). The fluorescence intensity of R6G had been increased sharply. Erythromycin diminished the fluorescence intensity of R6G. The detection limit was up to 0.316 mg l⁻¹. The range of determining concentration of erythromycin was 0.75-15 mg l⁻¹. The relative standards deviation were 0.66-1.38% for six parallel determinations of erythromycin. The recoveries of erythromycin were 96.95-101.41%. The measurement was applied to the determination of capsules of erythromycin with good results.     

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.     

Diffusion Coefficients of Several Rhodamine Derivatives as Determined by Pulsed Field Gradient–Nuclear Magnetic Resonance and Fluorescence Correlation Spectroscopy

Rhodamine derivatives are popular, photostable fluorophores that are used in a number of fluorescent based techniques, including fluorescence correlation spectroscopy (FCS). Indeed, in FCS, both rhodamine 6G (R6G) and rhodamine 110 (R110) are used as calibration standards to determine the dimensions of the instrument confocal volume. In spite of a requirement for precise values of the diffusion coefficients, literature values are scarce and vary over an order of magnitude. In this paper, the diffusion coefficients of four rhodamine fluorophores (rhodamine 6G (R6G), rhodamine B (RB), rhodamine 123 (R123), rhodamine 110 (R110)) were determined by pulsed field gradient nuclear magnetic resonance (PFG-NMR) spectrometry and then validated by comparison with fluorescence correlation spectroscopy. With the objective of validating the FCS calibration, diffusion coefficients of several dextrans and a polystyrene nanoparticle were also determined and compared with literature values or theoretical values that were based upon the Stoke–Einstein equation. The work presented here lead us to conclude that the diffusion coefficients for R6G and R110 have generally been underestimated in the literature. We propose revised values of 4.4 × 10⁻¹⁰ m² s⁻¹ for R110 and 4.0 × 10⁻¹⁰ m² s⁻¹ for R6G. Using the revised D value for R110 to calibrate the FCS instrument, diffusion coefficients have then been systematically determined for different conditions of pH, ionic strength and concentration. To correct for differences due to solvent effects (D₂O vs. H₂O), an isotopic correction factor, of 1.23, was determined from both FCS and from the solvent auto-diffusion coefficients obtained by NMR.     

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     

A new family of lasing dyes from an old family of fluors

We report the development of a new series of laser dyes and describe the performance of these materials. This work was spurred by the realization that few laser dyes have an optimally shaped fluorescence emission for lasing action. Most of the dipole strength of the transition is concentrated in the 0.0 band, where lasing cannot occur, and very little is concentrated in the vibrational satellites 0–1 and 0–2 where lasing is possible. The new dyes are unsymmetrical materials which may be considered as a hybrid of a rhodamine molecule and a fluorescein molecule (fig. 1), and we consider them to be cyclized merocyanines. One dye in particular, 6-dimethylamino-9-o-carboxyphenylxanthen-3H-one (labelled SNH-8), has given power output and time stability better than the preferred lasing dye Rhodamine 6G. The effects of dye structure and of acid-base transitions on lasing activity will be discussed briefly. The theory of band-shaping and the detailed optical parameters of the new dyes will be presented separately.     

Laser dye stability

The experimental parameters for solution temperature, solvent purity, and ultraviolet (uv) light removal have been examined as they affect the first-order bleaching constant, lasing slope efficiency, lasing threshold, and laser half-life of three dyes using air as the cover gas. A±10°C change from the ambient temperature was found to reduce the lasing output of solutions of the dyes rhodamine 6G, LD-490, and coumarin 102. Improving the purity of the solvent made no dramatic effects but did tend to yield somewhat lower bleaching rates and longer lasing lifetimes. The first-order bleaching constant for the dye LD-490 in several solvents was found to decrease in the order methanol >95% ethanol>ethanol. Although LD-490 in ethanol had twice the laser lifetime of that in methanol, the use of uv light filtration reversed this order. However, LD-490 still bleached faster in methanol than it did in ethanol. Interestingly using the uv filter, germicil quartz, did not decrease the lasing slope efficiency, but it made a slight increase in both the lasing slope efficiency and the lasing threshold. The use of the more strongly absorbing pyrex filter did, however, decrease the lasing slope efficiency as well as increase the threshold.     

Emission of Concentrated Solutions of Organic Compounds Excited with High-Power Laser Radiation

Specific features of emission of concentrated (C 1.2·10¹⁹ cm^–3) solutions of organic molecules (rhodamine 6G, rhodamine C, phenalemine 512, and substituted paraterphenyl (LOC-1)) are investigated as functions of the exciting photon energy (at _exc = 308 and 532 nm) and power density of exciting radiation (up to 1 GW/cm²). One of the observed emission types – band emission – is studied. The intensity of band emission (its short- and long-wavelength maxima) is investigated versus the exciting radiation power density, and its time and polarization characteristics are also analyzed. The results obtained together with the specific features of the emission spectrum of concentrated rhodamine-C solution, measured after passage of sounding radiation with maximum at the wavelength equal to that of the short-wavelength maximum of band emission, demonstrate that the band emission is simply superfluorescence.     

回音壁模式光纤激光器的阈值特性研究

研究了一种新型光纤激光器——消逝波激励的回音壁模式光纤激光器的阈值特性.将不同直径的石英光纤分别浸入低折射率的罗丹明6G乙醇和乙二醇混合溶液中,采用沿光纤轴向光抽运消逝波激励染料增益的方式,发现回音壁模式光纤激光辐射的阈值能量和混合溶液的折射率存在不同的依赖关系.随折射率的增加,对小直径光纤,阈值能量随之增加;对大直径光纤,阈值能量单调缓慢递减;对直径适中的光纤,阈值能量先减后增,存在一个和最小阈值能量对应的最佳折射率.用消逝波激励的回音壁模式激光理论,导出了回音壁模式光纤激光的阈值能量公式.理论计算曲线 关键词： 光纤激光器 回音壁模式 激光阈值 消逝波     

Ionic Equilibria of Fluorophores in Organized Solutions: The Influence of Micellar Microenvironment on Protolytic and Photophysical Properties of Rhodamine B

Ionic equilibria and fluorescence decay of rhodamine B were studied in micellar solutions of sodium n-dodecyl sulfate (SDS) with various additives (NaCl, pentanol-1, crown ether, and tetra-n-butyl ammonium salt), and five nonionic surfactants (Brij 35, nonyl phenol 12, Triton X-100, Triton X-305, Tween 80), as well as in -cyclodextrin solutions. The apparent dissociation constants, , of rhodamine B (HR⁺ R + H⁺) were obtained. The distribution of the dye species HR⁺ and R in the ultramicroheterogeneous systems was studied using absorption and emission spectra, fluorescence life-times, , and the plots of p versus surfactant concentration. The p values under conditions of complete binding, p , were found to be markedly higher than that in water . The medium effects, , in organized solutions studied are in accord with the charge type of the acid-base couple +/±, confirming the zwitterionic nature of rhodamine B neutral species. Both and a values of the dye were shown to sense the changes in the micellar microenvironments, and the possibility of using rhodamine B as an interfacial acid-base indicator, for example, for monitoring of surface potentials and of bulk ionic strength, were demonstrated.     

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.     

Luminescent spectral properties of rhodamine derivatives while binding to serum albumin

We have studied the effect of blood serum albumin on the absorption and fluorescence spectra of rhodamine C (RC), rhodamine 6G (R6G), and rhodamine 3B (R3B). Interaction of the dye with protein is assessed using the binding parameters: binding constants and concentrations of binding sites. We have studied the effect of temperature on the binding parameters. We have observed that heating a mixture of the dye solution with protein for 30 min leads to an increase in the binding constant for rhodamine 3B with protein by a factor of 2, while the concentration of binding sites increases by a factor of 2.3. This is explained by features of the globular protein structure and a change in its conformation when heated. We have shown that rhodamine 3B at a concentration of 10⁻⁵ M is the most effective among the studied rhodamine dyes for application as a fluorescent probe when studying conformational changes in blood serum protein. Report given at the Third International Conference on Liquid State Physics: Current Problems, May 27–31, 2005, Kiev, Ukraine. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 380–384, May–June, 2006.     

Influence of the Structure of a Macromolecular System on the Processes of Association of Molecules of Rhodamine 6G in Aqueous‐Polyelectrolytic Solutions

The processes of association of rhodamine6G molecules in aqueous solutions of polyacrylic acid are studied by spectroscopic methods. The efficiency of formation of the dimers of rhodamine 6G as a function of the concentration of the polyelectrolyte and its chain length is established. The angles between monomer molecules in the dimers of rhodamine 6G are determined for different concentrations of the polyacrylic acid and lengths of the polyion chain.     

Efficient amplification of sub-picosecond pulses of a non-CW dye laser

Efficient amplification in a dye laser amplifier is investigated theoretically and experimentally. A five-level rate equation approach is considered including rotational relaxation of the dye molecules. The effects of the pump pulse duration and of the parameters of the input pulse are discussed. The results are compared with experimental data for 0.5 ps pulses of a pulsed dye laser. Conversion efficiencies >10% are achieved for a single pass amplifier using Nd:YAG pump pulses of 2 ns while an effective fluorescence lifetime of 1.7±0.2 ns is determined for the gain medium rhodamine 6G. The triple pass amplifier stage of the laser system achieves an energy conversion of 4% with 40 J output pulses.     

The influence of silver nanoparticles on the stimulated luminescence of rhodamine 6G solutions

The influence of silver nanoparticles on the spontaneous and stimulated luminescence of rhodamine 6G molecules in aqueous solutions is studied. It is found that the laser photoexcitation of the dye solution gives rise to spontaneous fluorescence, which, with increasing pump power, transforms into stimulated laser radiation and superluminescence. Addition of silver nanoparticles to rhodamine 6G solutions enhances all types of luminescence and lowers the generation threshold for both types of the stimulated emission. The dependences of the laser radiation and superluminescence intensities on the concentration of silver nanoparticles correlate with the data on the spontaneous fluorescence.     

Characterisation of solid-state dyes and their use as tunable laser amplifiers

This paper reports on the spectroscopic and photo physical characteristics of solid-state dyes and their use as tunable high-gain laser amplifiers. A comparison of the absorption and fluorescence spectra is made for the dyes pyrromethene 567, pyrromethene 597, pyrromethene 650, rhodamine 6G in the solid hosts, polymethyl methacrylate, polycom and ormosil, and compared to the case of the dyes in the solvent methanol. Results show a reduced Stokes shift and an increased fluorescence lifetime for dyes in the solid hosts compared to the solvent. The use of pyrromethene 650 in polymethyl methacrylate as a tunable laser amplifier was investigated. The dye amplifier was shown to exhibit photo-induced birefringence, and the fluorescence polarisation and intensity dependent anisotropy effects of gain and refractive index was characterised. The molecular reorientation time for pyrromethene 650 in the solid host was calculated to be 6.8 ns. The solid-state dye exhibited a single pass gain of 500at 616 nm. The saturation behaviour was investigated and values of emission cross-section determined. Operation of the solid-state dye in a laser oscillator showed effects of strong shift in the lasing wavelength as a function of the cavity Q due to the small Stokes shift of the dye in the solid host. PACS 42.55.Mv; 42.50.Lh; 42.70.Jk     

A Rhodamine-Based Off�COn Fluorescent Chemosensor for Selectively Sensing Cu(II) in Aqueous Solution

A novel chromogenic and fluorogenic chemosensor RhB-pMOSal comprising a rhodamine fluorophore and a salicylaldehyde receptor being connected by an iminohydrazine link was synthesized and fully characterized. Its sensing behavior toward various metal ions in neutral aqueous solution was investigated by absorption and fluorescence spectroscopy. RhB-pMOSal exhibited a reversible and sensitive ??turn-on?? response of absorption and fluorescence toward Cu²⁺ in aqueous acetonitrile solution. Approximate 65 and 6-fold enhancement in the absorbance at 556 nm and fluorescence intensity at 573 nm were estimated when equivalent Cu²⁺ was added to the RhB-pMOSal solution. Under the same conditions, RhB-pMOSal displayed more sensitive than a reported analogue RhB-Sal to Cu²⁺ ion. The competition experiments for Cu²⁺ mixed with common metal ions exhibited no obvious change in absorption and emission except Cr³⁺ ion that can induce the fluorescence quenching of RhB-pMOSal to some extent.     

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.