Dispersion of Lifetimes of Excited States of Single Molecules in Organic Matrices at Ultralow Temperatures
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Dispersion of Lifetimes of Excited States of Single Molecules in Organic Matrices at Ultralow Temperatures M. G. Gladusha,b,c, T. A. Anikushinaa,b, A. A. Gorsheleva, T. V. Plakhotnikd, and A. V. Naumova,b,c,* a
Institute of Spectroscopy, Russian Academy of Sciences, Troitsk, Moscow, 108840 Russia of Theoretical Physics, Moscow State Pedagogical University, Moscow, 119991 Russia c Moscow Institute of Physics and Technology (State University), Dolgoprudnyi, Moscow oblast, 141700 Russia d School of Mathematics and Physics, University of Queensland QLD 4072, St Lucia, Brisbane, Australia *e-mail: [email protected]
b Department
Received September 26, 2018; revised September 26, 2018; accepted November 7, 2018
Abstract—Fluorescence excitation spectra of single terrylene molecules in transparent naphthalene and polyethylene matrices at ultralow (30–100 mK) temperatures have been studied under the conditions where the widths of zero-phonon spectral lines are determined only by the lifetime T1 of the excited electronic state. The experimentally observed dispersion of T1 values for identical molecules is attributed to local field effects, which are responsible for the dependence of T1 on the effective value of refractive index n of the matrix, which is characteristic of the localization region of each molecule. It has been shown that the dependence T1(n) for ensembles of point emitters in organic matrices is satisfactorily explained within the model of a “virtual cavity” around the emitter inside a continuous medium, as well as within the developed quantum kinetic approach including various contributions of the local environment to the lifetime T1. The recalculation of average T1 values to the corresponding n values with the use of the expressions obtained for T1(n) has shown that the difference of the calculated refractive indices of naphthalene and polyethylene from the well-known tabulated n values is less than 1%. DOI: 10.1134/S1063776119030038
1. INTRODUCTION The spectroscopy and microscopy (below, spectromicroscopy) of single molecules have been actively developed during the last two decades and are currently one of the most topical interdisciplinary scientific fields. The spectromicroscopy of single molecules is particularly informative at cryogenic temperatures, at which zero-phonon lines corresponding to purely electronic transitions of emitting centers can be observed [1–5]. The analysis of zero-phonon lines of single organic dye molecules allows the study of intraand intermolecular processes in impurity solids because the parameters of zero-phonon lines (linewidth, frequency, intensity, and time dynamics) are sensitive to the parameters of the local environment, i.e., generally to the static and dynamic parameters of local fields. The effect of the local environment of the matrix on the parameters of zero-phonon lines is usually discussed in the context of the interaction of an electronic transition of the impurity with localized tunneling and phonon excitations. The former excitations
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