Optische Spektren und Wanderungsmechanismen von Triplettexcitonen in reinen Naphthalinkristallen/Optical Spectra and Transport Mechanism of Triplet Excitons in Pure Naphthalene Crystals

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Abstract
Phosphorescence spectra of pure naphthalene and perdeutero-naphthalene crystals have been investigated between 4.2 and 300 K. Free-triplet exciton emission can be observed above 40 K only. The temperature dependence of phosphorescence line-width and line-shape has been studied between 60 and 300 K. With increasing temperature the lines are strongly broadened and become asymmetric. Above 150 K they show a red-shift (60 cm-1 at 300 K). The analysis is based on the decomposition of the lines into two components: an unshifted Lorentzian part resulting from coupled coherent and incoherent exciton motion and a sideband contribution built up with the phonon density of states of the naphthalene crystal. The Lorentzian line width is proportional to temperature. The degree of incoherence of exciton motion and characteristic parameters for the energy transfer mechanism are evaluated.