Kinetics of fluorescence polarization for solid bichromophore solutions in intense pulse excitation

The kinetics of fluorescence polarization in intense pulse excitation of solid disordered solutions of bichromophores that consist of complex molecules of two types between which there can be inductiveresonance transfer of electron-excitation energy is theoretically investigated. Variants of fluorescence excitation by single pulses and pulse trains are considered. The lifetime of the fluorescence of a given solution increases with the intensity of the exciting pulses. The possibility of controlling the duration of fluorescence attenuation for donor molecules incorporated into the bichromophores by the action of luminescence radiation at the frequency of acceptor-molecule absorption on the solution is demonstrated. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii Vol. 65, No. 4, pp. 546–550, July–August, 1998.     

Quenching of the fluorescence of solutions of complex molecules by nonradiative transfer of electronic-excitation energy to a saturable acceptor

The study puts toward a theoretical model describing the fluorescence parameters for concentrated solid solutions consisting of complex molecules of two types (donor-acceptor) with nonradiative transfer of electronic-excitation energy with intense pulse excitation. Consideration is given to the dynamics of quenching of the luminescence of the donor molecules due to transfer of electronic-excitation energy to the acceptor molecules. Numerical results are presented in the form of approximation formulas. To whom correspondence should be addressed. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 652–656, September–October, 1999.     

Spectral characteristics of luminescence of solutions of complex molecules under conditions of electronic excitation transfer to a saturable acceptor in the case of inhomogeneous broadening of electronic energy levels

Spectral characteristics of solutions of complex molecules under conditions of inhomogeneous broadening of energy levels are considered in the case when the nonlinear dependence of the population of molecular states on the excitation intensity is determined not by saturation of molecular levels but by exchange of the electronic excitation energy with the environment. Calculations have shown that the dependence of the position of the fluorescence spectrum on the excitation frequency is nonmonotonic in solutions of the type and varies substantially with the excitation intensity. Belarusian State University, 4, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 164–168, March–April, 1997.     

Luminescence of complex organic molecules upon electron excitation

Pesults of investigation of the luminescence of complex organic compounds upon excitation with electrons of various energies are reported. Data on spectra of energy losses of electrons, fluorescence excitation cross sections and functions, fluorescence emission spectra, fluorescence kinetics, polarization, and energy yield, effects of impurity gases, and theoretical analysis of the processes taking place in the system are presented. Results of investigation of the luminescence of complex molecules in electric discharges (dc, pulsed, high-frequency, non-self-maintained, and plasma-beam) and in a condensed state (solutions, molecular crystals, and thin solid films) are discussed. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk 220072, Belarus. Transtated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 694–708, September–October, 1998.     

Room‐temperature luminescence decay of colloidal semiconductor quantum dots: Nonexponentiality revisited

While time‐resolved luminescence spectroscopy is commonly used as a quantitative tool for the analysis of the dynamics of photoexcitation in colloidal semiconductor quantum dots, the interpretation of the virtually ubiquitous nonexponential decay profiles is frequently ambiguous, because the assumption of multiple discrete exponential components with distinct lifetimes for resolving the decays is often arbitrary. Here, an interpretation of the room‐temperature luminescence decay of CdSe/ZnS semiconductor quantum dots in colloidal solutions is presented based on the Kohlrausch relaxation function. It is proposed that the decay can be understood by using the concept of Förster resonance energy transfer (FRET) assuming that the role of acceptors of photoexcitation energy is played by high‐frequency anharmonic molecular vibrations in the environment of the quantum dots. The term EVFRET (Electronic ‐ Vibrational Förster Resonance Energy Transfer) is introduced in order to unequivocally refer to this energy transfer process.

     

Determination of intramolecular energy-transfer efficiency in ytterbium chelates

The quantum yield of²F_5/2 →²F_7/2 luminescence of the Yb³⁺ ion has been measured for ytterbium tris-thenoyltrifluoroacetonate upon excitation in the UV S₀ → S₁ absorption band of a ligand and in the IR²F_7/2 →²F_5/2 absorption band of the Yb³⁺ ion. It has been established that the quantum efficiency of intramolecular transfer of electron excitation energy from the lowest triplet state of the ligand to the excited²F_5/2 level of Yb³⁺ is equal to unity. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 539–542, July–August, 2000.     

Processes of Electron Excitation Energy Conversion in Europium Tris‐Naphthoyltrifluoroacetonate

The absolute quantum yield and duration of ⁵ D ⁷ F _j luminescence of the Eu³⁺ ion in europium trisnaphthoyltrifluoroacetonate has been measured on excitation of luminescence in the UV S ₀ S ₁ absorption band of the ligand in the temperature range 77–365 K. Based on the analysis of the experimental dependences obtained and solution of the balance equations for stationary and nonstationary cases, we have developed a new approach to the determination of the scheme and rate constants of actual transitions. The rate constants of all processes of electron excitation energy conversion have been determined. The role of the state with charge transfer in these processes has been revealed.     

Energy yield of fluorescence of complex organic compounds upon electron excitation

With use of electron energy loss spectra for vapors of anthracene, perylene, 1,4[di(2,5-phenyloxazolyl)] benzene, and paratherphenyl the energy yields of fluorescence are calculated for electron collision. It is shown that they are considerably smaller than those for optical excitation conditions. Deceased Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 146–148, January–February, 1998.     

Extreme narrowing of bands in the fluorescence excitation spectra of organic molecules in solid solutions

Extreme narrowing of bands in the fluorescence excitation spectra of some organic molecules is found. This narrowing is observed when the excitation spectrum of a narrow spectral interval of the fluorescence band is recorded. The effect is observed in a wide variety of matrices and permits one to determine exactly the vibronic structure of the excited electronic state of the dissolved molecule.     

Ce~(3+)-Yb~(3+)共掺YAG荧光粉量子剪裁发光的浓度及温度特性

采用高温固相法制备了不同掺杂浓度的YAG∶1%Ce~(3+),x%Yb~(3+)(x=5,10,15,20,25)系列荧光粉。在450 nm蓝光激发下,测试了样品的发射光谱,得到了中心波长在550 nm的可见宽带发射(Ce~(3+):5d→4f)和1 030 nm的近红外发射(Yb~(3+):2F_(5/2)→2F_(7/2))。可见和近红外发射强度随Yb~(3+)掺杂浓度的变化表明Ce~(3+)到Yb~(3+)存在能量传递过程,并得到Yb~(3+)的猝灭浓度为15%。在低温条件下(80~300 K)测试YAG∶1%Ce~(3+),15%Yb~(3+)样品的发射光谱和拉曼光谱,通过对其量子剪裁发光温度特性的分析,描述了基质声子在Ce~(3+)到Yb~(3+)的能量传递过程中起到的重要作用。     

Theoretical models for interisomer transitions of complex molecules and their spectral manifestations

We have used computer simulation to compare theoretical models for describing interisomer transitions of complex molecules and their spectral manifestations. We have shown that the kinetics of the intramolecular processes and time-resolved spectra, taking into account quantum beats between resonant (bound) states of the isomers (or isolated level subsystems for one isomer form), can be described not only by using a general molecular model in which the resonant levels of the subsystems act as a single level of a mixed state, with a time-dependent wave function in the form of quantum beats, but also by using a model interpreting the beat effect as a nonradiative transition. These models are completely equivalent: the parameters describing them have the same values, and numerical differences in the results obtained are no greater than 1% and are due to numerical round-off errors in the calculations and not differences between the models. The second model is preferred because it is graphically clear and conventionally used for describing and interpreting intramolecular processes, but it does take somewhat longer (∼10%) to run the simulation. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 36–41, January–February, 2006.     

Anti-Stokes luminescence of microcrystals of AgCl0.95I0.05 solid solutions with adsorbed organic dye molecules

We have studied the effect of the characteristic features of aggregation of some organic dye molecules during adsorption on the parameters of low-temperature sensitized anti-Stokes luminescence (SASL) in microcrystals of AgCl_0.95I_0.05 solid solutions. We have demonstrated the possibility in principle of varying the position of the maximum in the SASL excitation spectrum and its intensity by varying the concentration of the dye molecules deposited on the surface of the AgCl_0.95I_0.05 microcrystals. We have observed that the intensity of SASL excitation for these samples increases as different types of dye aggregates form on their surface. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 592–596, September–October, 2006.     

An unique method of determining the excitation energy migration coefficient in organic liquid scintillators

An experimental method is described to determine the excitation energy migration coefficient Λ in an organic liquid scintillator by measuring the energy transfer rate parameterk ₃ and the quenching rate parameterk _7b as a function of temperature in the range of 20°C–70°C. In this experiment we have used toluene as donor, ethyl-1-n-butyl-2-methyl-5-hydroxyindole-3-carboxylate (EBMHC) as acceptor and bromobenzene as quencher. The values of Λ are found to be in good agreement with literature values. Hence this method can be used to determine the migration coefficient in organic liquid scintillators.     

Investigations of the excitation energy transport mechanism in donor-acceptor systems

Measurements of fluorescence quantum yield _D/_oD of Na-fluorescein (donor; D) versus concentration of rhodamine B (acceptor; A) in viscous solutions have been carried out. The donor concentration in these solutions was as follows:C _D=2·10^–2 M (system I), 1.5·10^–2 M (II), 10^–2 M (III), 3·10^–3 M (IV), and 5·10^–5 M (V). The experimental results have been compared with current theories of nonradiative electronic energy transfer (NEET). In the case of very strong migration (systems I, II, and III), a significant influence of correlations (between configurations of D and A molecules in the surroundings of successively excited donors) on quantum yield _D/_oD has been determined. Experimental values have been found to be clearly higher in comparison with those predicted theoretically. The influence of possible factors on the decrease in the effectiveness of excitation energy transport to traps-acceptors in systems of very strong migration has been discussed.Dedicated to Professor A. Kawski on the occasion of his 65th birthday.     

Triplet-triplet transfer of electronic energy upon nonequilibrium vibrational excitation of triplet molecules

The specific features of the triplet-triplet (T-T) transfer of electronic excitation energy in a gas phase upon nonequilibrium vibrational excitation of the triplet molecules of a donor were studied for an anthraquinone-diacetyl donor-acceptor pair using the time-resolved slow fluoresence of anthraquinone and sensitized phosphorescence of diacetyl. It is shown that in the gas phase, which allows regular control of the number of collisions, competition between the processes of T-T transfer and intermolecular vibrational relaxation is observed for nanosecond time resolution. The T-T transfer rate for the molecular system investigated exceeded the rate of intermolecular vibrational relaxation k_V in the triplet state T₁ of the donor. The effectiveness of the T-T transfer of energy by vibrationally excited molecules turned out to be higher than the effectiveness of transfer by thermalized ones, but even the highest of them was much less than unity. An increase in the equilibrium temperature of vapors led to a decrease in the effectiveness of transfer for both vibrationally excited and thermalized triplet molecules, thus indicating the importance of the collisional complex in the intermolecular process studied. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 474–479, July–August, 2000.     

The role of cation vacancies in excitation mechanism of re-ions in alkaline-earth sulphides

Abstract

The VUV-excitation spectra and thermostimulated emission for intrinsic and impurity luminescence of alkaline-earth sulphides doped by cerium have been investigated. The intensity of activator emission is higher in samples with artificially created cation vacancies. The role of cation vacancies is displayed as a result of the common analysis of the temperature dependence of impurity luminescence with the curves of the thermostimulation of the hole traps created due to the presence of the cation vacancies. For room temperatures the hole traps on cation vacancies become unstable. Therefore the trap level of cation vacancy serves as a bridge for the capture of holes from the valence band to 4f RE level.     

Signs of structural changes in molecules in IR spectra with pulsed heating

We have shown that in slow thermal reactions of complex molecules, effects of nonradiative transitions due to quantum beats between resonant states of the combining molecular structures can be observed in conventional (without high time resolution) IR absorption spectra, as oscillations in the intensities of individual lines. We suggest a method to ensure the required level of coherence for the oscillations in an ensemble of molecules, based on application of pulsed heating to the molecular system. Detection of the qualitatively new effects by traditional IR spectroscopy methods, including their quantitative characteristics, considerably increases the information content of the spectral data obtained and makes it possible to use such highly developed experimental methods to study chemical reactions, including the reaction dynamics. The range of these reactions is quite broad, encompassing both “laboratory” and “natural” (geochemistry, ecology, etc.) processes with characteristic times on the order of minutes or more. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 738–743, November–December, 2007.     

Concentration dependence of the quantum yield of luminescence of Tm<Superscript>3+</Superscript> ions in gadolinium oxychloride

The concentration dependence of the quantum yield of luminescence of Tm³⁺ ions in an oxychloride matrix has been measured in individual bands of their luminescence excited at different wavelengths. The concentration dependences of the quantum yield of luminescence were calculated with allowance for the effect of the unintentional impurity of rare-earth ions. The cross-relaxation nature of the concentration dependence of the rare-earth ion luminescence is discussed.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 759–765, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Quenching of fluorescence of porphyrin molecules in their association in binary solutions

It has been established that the absorption and fluorescence spectra of octaethylporphin (OEP), mesotetraphenylporphin (TPhP), and its complex with zinc (Zn-TPhP) in glycerol doped with dimethylformamide (DMF) or ethanol differ from the analogous spectra of these compounds in ethanol or DMF, which is due to the formation of associates of porphyrin molecules in solutions of OEP, TPhP, and An-TPhP with glycerol. For TPhP and Zn-TPhP, these differences are small, the maxima of the bands are shifted toward longer wavelengths by 3–5 nm, and their halfwidths are increased by ∼ 16%; for OEP these changes are more significant. It is shown that the duration of fluorescence of associates is much shorter than that of monomers. The probable mechanisms of quenching of the fluorescence of dimers (oligomers) of molecules were considered. It has been suggested that one of the reasons for the increased rates of deactivation of the excited states of dimers (oligomers) may be the decreased energy interval between the excited and ground states of associates as compared with that of monomers. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 21–25, January–February, 2000.