Decay kinetics of the delayed annihilation fluorescence of aromatic molecules in Langmuir-Blodgett films

Triplet states of aromatic molecules of the anthracene type in Langmuir-Blodgett films are investigated. It is established that the principal channel for the relaxation of T ₁ states is bimolecular triplet-triplet annihilation. The observed nonexponential decay kinetics of delayed annihilation fluorescence is discussed within the formal-kinetic and percolation models. Fiz. Tverd. Tela (St. Petersburg) 41, 736–739 (April 1999)     

Three-photon annihilation of the electron-positron pairs

Three-photon annihilation of the electron-positron pairs (=(e⁻,e⁺)-pairs) is considered in the electron rest frame. The energy of the incident positron can be arbitrary. The analytical expression for the cross-section of three-photon annihilation of the (e⁻,e⁺)-pair has been derived and investigated.     

Features of sensitized phosphorescence and delayed annihilation fluorescence spectra of coronene in frozen solutions

We have studied the sensitized phosphorescence spectra of coronene in toluene and its delayed annihilation fluorescence spectra in n-decane at 77 K. We show that as a result of perturbation of electronic states by exchange interactions, intensity redistribution occurs in both the sensitized phosphorescence spectrum and the delayed annihilation fluorescence spectrum. The nonzero probability of the symmetry-forbidden radiative 0–0 transition is explained by the lower symmetry of the bimolecular system compared with the symmetry of the coronene molecule.     

Contributions to the theory of singlet exciton decay into pairs of triplet excitons in organic molecular crystals

Probability of singlet exciton decay into pairs of triplet excitons in organic molecular crystals is calculated. The dependence of the calculated probability on the separation of created pairs of triplet excitons, on temperature as well as on variations of equilibrium positions of molecules caused by changes of the state of electron excitations in the crystal is discussed. In conclusion there is given the estimation of the order of the probability value.Na Slovance 2, Praha 8, Czechoslovakia.     

Regge behaviour for inclusive annihilation and decay processes

By exploiting annihilation processes it is shown that inclusive experiments are also relevant at low energies, if duality holds.     

F(o)rster双分子猝灭作用对卟啉侧链聚合物荧光衰变的影响

通过采用时间分辨荧光光谱技术测量了一种卟啉侧链聚合物薄膜:卟啉丙烯酸酯-苯乙烯共聚物poly[porphyrin acrylate-styrene] (P[(por)A-S])在高激发密度下的瞬态荧光特性.实验发现,P[(por)A-S]样品的荧光衰减随聚合物分子浓度的增大而加快.利用Frster机制的双分子猝灭理论对其浓度猝灭的原因进行了分析,理论结果与实验结果符合较好.研究表明,在高激发密度的情况下,Frster机制的双分子作用是加快卟啉侧链聚合物初始荧光衰减和降低其发光效率的主要因素.     

On the four-photon annihilation of the electron-positron pairs

The four-photon annihilation of electron-positron pairs is considered. In our treatment the energies of the colliding particles can be arbitrary. We also discuss the lower-energy limit of the cross-section of three-photon annihilation of the (e^-, e⁺)-pair.     

Coherent γ-emission by stimulated annihilation of electron-positron pairs

The possibility of using stimulated emission from the recombination of electron-positron pairs for obtaining coherent γ-rays is considered. The critical number of pairs needed for the process is calculated.     

Kinetics of positron annihilation in ionic crystals

A kinetic scheme of decay of positron and positronium states for the general case — a real ionic crystal with point lattice defects and a developed surface — is examined. The properties of positron and positronium states in the volume of the crystal, positron and positronium color centers, and surface positron and positronium states, are analyzed. It is shown that all the available experimental data qualitatively confirm the conclusion of an annihilation mechanism based on the postulated kinetic scheme of positron annihilation in real ionic crystals.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 50–55, September, 1977.     

Kinetics of exciton-exciton annihilation in molecular crystals

The theoretical investigation of the time dependence of the concentration of incoherent excitons formed by pulsed pumping is carried out. The basis of this investigation is a system of an infinite number of coupled equations for multiparticle distribution functions. Using the Kirkwood method of uncoupling, this system is reduced to a system of differetial equations for one- and two-particle distribution functions. The algorithm for calculating these equations by means of an electronic computer is developed.A simple phenomenological differential equation for exciton density has been obtained. The solution of this phenomenological equation coincides with good accuracy with the solution obtained by numerical integration of the above-mentioned system of differential equations for one- and two-particle distribution functions.     

Production and decay of polarized hyperon-antihyperon pairs

Polarized hyperon-antihyperon pairs shed light on various unresolved puzzles in contemporary physics: How the strong interaction confines quarks into hadrons, how accurately the Standard Model describes microcosmos and even why our universe consists of so much more matter than antimatter. Thanks to their weak, parity violating decays, hyperons reveal their spin properties. This can be exploited e.g. the decomposition of the electromagnetic structure of hyperons, precision tests of flavour symmetry and searches for CP violation. At the BESIII experiment at BEPC-II, Beijing, China, hyperon-antihyperon pairs can be produced in abundance. Recently collected large data samples have triggered the development of new methods that provide unprecedented precision and a plethora of new results have emerged. When applied at future high-intensity facilities like PANDA and STCF, precision physics will be taken to a new level which can contribute to the solution to the aforementioned puzzles.     

Pulsed UV laser for fluorescence decay measurements

Second harmonic generation in a non-linear optical crystal is utilized to obtain pulsed UV emission (λ = 2573 Å) which exhibits peak powers of greater than 1 W at repetition rates ranging from single pulse to 1 MHz. Such a system is useful for measuring fluorescence decay times in UV excitable materials which are longer than 10 ns in duration.     

Effect of magnetic field on triplet excitons annihilation in Langmuir-Blodgett films

We study the effect of an external magnetic field on annihilation of triplet excitons of aromatic molecules in Langmuir-Blodgett films. Differences in the magnetic effect in relation to the number of layers, temperature, and recording time of annihilation delayed fluorescence are determined.     

Production and decay of W boson in electron-positron annihilation

We study the characteristics of the μe events due to e⁺e^? → W⁺W^? and the subsequent leptonic decay of W^±, in the Weinberg-Salam model. The differential cross section for W production is given for non-polarized electron-positron beams as well as transversely polarized beams. The energy angle distributions as well as angular correlations of the final μe events are presented for beam energy of 100 + 100 GeV. Potential backgrounds are also discussed.     

Mechanism of the electron spin polarization of excited triplet states caused by the mutual annihilation of triplet states

A new mechanism of the triplet spin polarization is considered qualitatively and quantitatively. The spin polarization arises due to the spin-selective triplet-triplet annihilation and the subsequent spin dynamics in the spin-correlated pairs of triplets. With the time-dependent perturbation theory the simple rules are found which specify the polarization pattern of triplets.