Spectral-Kinetic Properties of Laser Dyes in Active Elements on the Basis of Sol-Gel Matrices

The absorption and photoluminescence spectra as well as the photoluminescence lifetimes of laser dyes (Phenylamine 430, Rhodamine 6G, Rhodamine 6G zwitterion, Rhodamine 4C, and Rhodamine 101) in new matrices are studied. These matrices represent the hybrid of two types of porous glasses (microporous and sol-gel glass). Chemical transformations of the dye molecules in the matrices are not found. The dye dimers mentioned above are also absent for concentrations up to 10^-4 M. The luminescence efficiencies of the dyes in the matrix and in the ethanol solutions are compared. The difference in concentration dependences of the photoluminescence spectrum of Rhodamine 6G in the matrix and ethanol solution is found and discussed. The collective emission of the dyes in new matrices is observed at a power density of exciting radiation of 10²⁵ cm^-2s^-1 and a concentration of 10^-4 M. The energies and collective emission spectra of the dyes in the matrix are compared with those in the solutions.     

Influence of temperature and ethanol content on aggregation of rhodamine 6G molecules in aqueous ethanol solutions

The effect of temperature on absorption spectra of Rhodamine 6G at concentrations of 10⁻⁶ and 10⁻³ M in water:ethanol solutions of various ethanol content was studied. The dimeric molecular fraction of Rhodamine 6G (10⁻³ M) was found as a function of temperature and ethanol content in the aqueous solution. It was shown that the absorption spectrum of Rhodamine 6G dimers (10⁻³ M) is dependent on temperature and ethanol content in the aqueous solution. Based on the relationship between J-and H-bands in the absorption spectrum of Rhodamine 6G dimers, both the angle between planes of associated Rhodamine 6G dye molecules and the free enthalpy of association were calculated. The structure of Rhodamine 6G dimers depends essentially on the ethanol content and aqueous ethanol solution temperature while experiencing the most temperature changes at an ethanol concentration of 25%. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 640–645, September–October, 2008.     

Optical properties of Rhodamine B and Rhodamine 6G on silver surfaces

The transmission spectra of Rhodamine B and Rhodamine 6G dyes coated on silver island films for various thickness were recorded. A strong coupling between the silver particle plasma resonance and the dye molecules is observed. The absorption of dye molecules increases when the absorption band of individual dyes and silver particles overlaps. In higher silver film thicknesses, transmission increases. The theoretical calculation using Maxwell-Garnett theory and Wang and Kerker’s results qualitatively supports the observed phenomenon. A red shift in the absorption peak of dyes on silver surfaces in comparison to solution phase absorption peak indicates photobleaching.     

Spectral-Luminescent Properties of Deposited Rhodamine 6G Films

We have investigated the absorption and fluorescence spectra of Rhodamine 6G thin (20–100 nm) films vacuum-deposited on solid dielectric substrates: quartz and borosilicate glasses and polymer films. By the absorption spectra several molecular absorption centers — monomers, dimers, and complex associates — have been revealed. For the first time luminescence of vacuum-deposited Rhodamine 6G films has been obtained and investigated. We classified it as fluorescence of plane dimers and dimers of the house-of-cards type and also as luminescence of complex associates. The dependence of the spectral composition of the films on the excitation wavelength in the 293–353 K temperature range has been studied. It has been proposed that amorphous Rhodamine 6G films obtained by the vacuum deposition method contain crystalline zones and microclusters of adsorbed water molecules.     

Investigation of Rhodamine 6G in oleic acid solution fluorescence under high pressure

Interesting behavior has been observed in the absorption spectra of the solution of Rhodamine 6G [C₂₈H₃₁N₂O₃Cl] in oleic acid [C₁₈H₃₄O₂] [K. Wieja et al., Pressure-induced changes in electronic absorption spectrum in oleic acid, High Press. Res. 30 (2010), pp. 130–134]. Application of high pressures to the solution has caused the reshaping of the absorption spectra curve, and the maximum of absorption has been shifted towards the longer wavelength. One of the most possible explanations of the changes in the absorption spectra is the formation of charge-transfer complexes in the solution. Pressure-induced changes of the VIS absorption spectrum in the mixture of Rhodamine 6G and oleic acid have been observed in comparison with the absorption spectrum of the mixture of Rhodamine 6G in ethanol. Moreover, changes have been observed in the fluorescence spectrum of the examined mixture, which indicated a fluorescent electronic band of a CT complex.     

Transient excited singlet state absorption in Rhodamine 6G

Transient excited singlet state absorption (ESSA) has been studied in Rhodamine 6G in ethanol using a nitrogen laser and nitrogen laser-pumped dye laser. Broad absorption with several submaxima and possible shoulders, which represent the vibrational structure, has been observed in Rhodamine 6G in the region, 4175–4640 Å. The position of the lowest vibrational level of the first excited singlet stateS ₁ has been determined from the crossing point of the long and short wavelength spectral wings of absorption and fluorescence respectively. The energy level scheme of the molecule has been obtained with the help of the absorption and fluorescence spectra recorded. The observed structure in ESSA has been tentatively interpreted to be due to transitions from the different vibrational levels ofS ₁ to one or more vibrational levels of the upper singlet electronic stateS ₄.     

Nanostructuring of thin Au films by means of short UV laser pulses

The particle size distribution, morphology and optical properties of the Au nanoparticle (NP) structures for surface enhanced Raman signal (SERS) application are investigated in dependence on their preparation conditions. The structures are produced from relatively thin Au films (10–20 nm) sputtered on fused silica glass substrate and irradiated with several pulses (6 ns) of laser radiation at 266 nm and at fluencies in the range of 160–412 mJ/cm². The SEM inspection reveals nearly homogeneously distributed, spherical gold particles. Their initial size distribution of the range of 20–60 nm broadens towards larger particle diameters with prolonged irradiation. This is accompanied by an increase in the uncovered surface of the glass substrate and no particle removal is observed. In the absorption profiles of the nanostructures, the broad peak centred at 546 nm is ascribed to resonant absorption of surface plasmons (SPR). The peak position, halfwidth and intensity depend on the shape, size and size distribution of the nanostructured particles in agreement with literature. From peak intensities of the Raman spectra recorded for Rhodamine 6G in the range of 300–1800 cm⁻¹, the relative signal enhancement by factor between 20 and 603 for individual peaks is estimated. The results confirm that the obtained structures can be applied for SERS measurements and sensing.     

Spectral–Luminescent and Generation Characteristics of a Gel–Like Gelatin Doped with a Dye

We present the results of comparative measurements of spectral–luminescent characteristics of Rhodamine 6G and Rhodamine C in water and water–gelatin solutions. We found that gelatin added to a water solution disaggregates the molecules of the dye. The maxima of the absorption and luminescence spectra of the solution shift then to the longwave region. The quantum yield of luminescence and the efficiency of generation of the solutions investigated are measured. The generation intensity of the gel is shown to depend on its composition and the dye selected. Measurement of spectral–luminescent characteristics of water–gelatin solutions makes it possible to select dyes that would generate most efficiently in gel solutions.     

Singlet-singlet energy transfer in liquid solution between Rhodamine 6G and benzophenone in presence of non-linear absorption

Results are presented on non-linear absorption of benzophenone in a methanol solution. Using a mixture of Rhodamine 6G and benzophenone, we show the possibility of singlet-singlet energy transfer between these two molecules.The experimental data give a value for the energy transfer probability of 10¹² M^?1 sec^?1.     

Localized Surface Plasmon Resonance of Cu@Cu2O core-shell nanoparticles: Absorption, Scattering and Luminescence

By co-deposition via RF-Sputtering and RF-PECVD methods and using Cu target and acetylene gas, we prepared Cu@Cu₂O core-shell nanoparticles on the a-C:H thin film at room temperature. Mie absorption of Cu cores, scattering from Cu₂O shell and luminescence that rises from carrier transfer in Cu@Cu₂O interface were employed to fit the whole range of visible extinction spectrum of these core-shells. From simulation it was found that scattering and luminescence have an important effect on the energy, width and shape of LSPR absorption peak. Shift of LSPR peak is more affected by the dielectric coefficient of shell than Cu core size particularly for Cu core diameter above 4 nm. Also, the LSPR absorption peak is damped by decreasing Cu core size and dielectric coefficient of shell. The energy of LSPR absorption peak is independent of shell thickness and host dielectric coefficient. The LSPR peak is damped by increasing shell thickness and host dielectric coefficient too. The scattering contribution in extinction spectra was affected more by shell size than dielectric coefficient. These points are important for detection techniques based on LSPR peak.     

I-scan thermal lens experiment in the pulse regime for measuring two-photon absorption coefficient

We present a new pump-probe mode-mismatched thermal lens method for pulse excitation aimed to the measurement of nonlinear absorption coefficient in optical materials. We develop a theoretical model based on the Fresnel diffraction approximation and their predictions are verified experimentally with samples of Rhodamine 6G and Rhodamine B in ethanol solution. The principal advantage of this technique is that it does not require any mechanical movement during measurement. Below we perform the new type of thermal lens experiment in the pulse regime for the measurement of nonlinear absorption coefficient in transparent samples and we demonstrate the validity of theoretical predictions using an alternative method to the classical thermal lens technique.     

Synthesis and luminescence properties of nanocrystalline Gd2O3:Eu by combustion process

The nanocrystalline Gd₂O₃:Eu³⁺ powders with cubic phase were prepared by a combustion method in the presence of urea and glycol. The effects of the annealing temperature on the crystallization and luminescence properties were studied. The results of XRD show pure phase can be obtained, the average crystallite size could be calculated as 7, 8, 15, and 23 nm for the precursor and samples annealed at 600, 700 and 800 °C, respectively, which coincided with the results from TEM images. The emission intensity, host absorption and charge transfer band intensity increased with increasing the temperature. The slightly broad emission peak at 610 nm for smaller particles can be observed. The ratio of host absorption to O²⁻-Eu³⁺ charge transfer band of smaller nanoparticles is much stronger compared with that for larger nanoparticles, furthermore, the luminescence lifetimes of nanoparticles increased with increasing particles size. The effects of doping concentration of Eu³⁺ on luminescence lifetimes and intensities were also discussed. The samples exhibited a higher quenching concentration of Eu³⁺, and luminescence lifetimes of nanoparticles are related to annealing temperature of samples and the doping concentration of Eu³⁺ ions.     

Luminescence study of LiGa5−xFexO8

Absorption, excitation, and luminescence measurements are presented for LiGa_5?xFe_xO₈ with concentrations x from 0.015 to 0.26. The emission and excitation data indicate that the red luminescence observed is due to the ⁶A₁(⁶S)←⁴T₁(⁴G) transition in the d⁵ configuration for Fe³⁺ in tetrahedral sites. Single-crystal samples allow direct absorption measurements for the first time and these indicate that most of the Fe³⁺ substitutes for Ga³⁺ in octahedral sites. Fine structure in the zero-phonon line and in the sideband is reported.     

Unusual induction of optical anisotropy in polymer media by low-intensity polarized x-rays

The induction of linear dichroism in (poly) methylmetacrylate films activated with Rhodamine 6G and its base in the spectral range of absorption of these dyes under the action of plane-polarized x-rays with wavelength 0.70Å and intensity 7.5·10⁴ quanta per second has been revealed. The phenomenon is discussed from the standpoint of the radiochemical analog of the photochemical polarization-induced selection of organic molecules with allowance for the structural characteristics of the polymer film components.     

基于银掺杂钠钙玻璃的荧光染料自发辐射增强

本文通过离子交换和后续热处理的方法在钠钙玻璃中引入Ag纳米颗粒, 并将Ag掺杂的钠钙玻璃作为衬底增强了钠钙玻璃和荧光染料罗丹明6G(R6G)的荧光辐射。Ag纳米颗粒的表面等离激元散射增强了掺杂玻璃的荧光, 而R6G的增强荧光辐射则源于掺杂玻璃与荧光染料之间的辐射共振能量转移。     

Water as a proton donor in excited state reactions of 6, 6′-biquinoline

6, 6′-biquinoline (BQ) in aqueous-alcoholic solutions exhibits doubleluminescence and two ESR signals in the triplet state. The structureless fluorescence band observed at room temperature was shown to be the result of the protonation of strongly basic¹ (BQ)^* (pK^* = 13). At low temperature the aggregation of the molecule has been observed. The low temperature absorption, luminescence, luminescence excitation spectra, and triplet ESR spectra of the aggregates have been measured and distinguished from the corresponding spectra of monomeric BQ.     

Turnable Second Harmonic Generation from an Organic Dye Laser

Abstract

Ultraviolet light has been generated from a Rhodamine 60 organic dye laser by frequency doubling with a KDP crystal. The second harmonic was tuned from 2900Å to 3000Å with peak powers of 40 watts.

Organic dye lasers have now been reported with output wave-lengths extending throughout the visible and near infrared^1-12. The tunability^4,6,13 and output energies now available in the visible protion of the spectrum suggest frequency doubling as a means of obtaining a tunable source of ultraviolet light. We wish to report the observation of tunable second harmonic radiation centered at 2950Å generated from the laser output of a 10^?4 molar solution of Rhodamine 6G dissolved in ethyl alcohol.     

Stimulated resonance Raman scattering of Rhodamine B

Stimulated resonance Raman scattering (SRRS) of the Rhodamine B (RhB) in the methanol (CH₃OH) or ethanol (C₂H₅OH) solutions have been observed. SRRS from RhB can be distinguished from the amplified spontaneous emission (ASE) of RhB with increasing the input laser energy. When the RhB is dissolved in the methanol or ethanol (10^?3 mol/L), the RhB have the different peak wavelengths of SRRS, ASE, fluorescence and absorption, respectively. SRRS can be amplified by the ASE gain when the SRRS is near the peak of the ASE, and the peak wavelength of SRRS coincides with the maximal intensity wavelength of ASE.     

Measurement of nonlinear properties and optical limiting ability of Rhodamine6G doped silica and polymeric samples

The third order nonlinear optical properties of Rhodamine6G (Rh6G) doped silica and polymeric samples have been investigated using single beam z-scan technique under excitation by the second harmonic of Nd:YAG laser beam (532 nm). The nonlinear refractive index, nonlinear absorption coefficient, real and imaginary parts of third order nonlinear susceptibility in the samples of silica and poly-methylmethacrylate (PMMA) matrices are measured. Thermal contribution to the nonlinear refractive index in case of undoped silica samples has been calculated in order to have better accuracy of the material response contribution to third order nonlinearity. The comparative study of the optical limiting performance of Rh6G doped silica and polymeric samples show that Rh6G doped silica is relatively superior for optical limiting applications.     

消逝波激励的双波段光纤回音壁模式激光辐射

将石英光纤浸入低折射率的染料溶液中后构成圆柱形微腔.采用轴向光抽运消逝波激励激光增益的方式,使增益区域局限在圆柱形微腔回音壁模式的模场区域内,由此显著地提高了抽运效率,增加了沿光纤轴向的增益长度.在一根石英光纤的轴向分段填入浓度同为2×10^-3mol/L的罗丹明6G和罗丹明B乙醇溶液,在567—576nm 和592—600nm的两个波长范围内同时获得回音壁模式的激光辐射;分段填入浓度为8×10^-4和8×10^-3mol/L的罗丹明B乙醇溶液, 关键词： 消逝波激励 圆柱形微腔 回音壁模式 双波段激光辐射