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1 December 1997 Stimulated emission in sexithiophene single crystals
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Temperature dependent steady state and transient photoluminescence (PL) measurements were performed on sexithiophene single crystals. As the temperature is lowered, three different sets of equally spaced peaks appear on the steady state PL spectrum. This behavior is interpreted in the frame of the molecular exciton theory. The lowest energy set is attributed to transitions from the lower Au excited state, resulting from the Davydov splitting of the 1Bu excited state of the isolated molecules. The highest energy set of peaks is ascribed to an excited Ag level. At low excitation levels, the transient PL follows a single exponential decay, with a time constant of 1.8 ns. When the excitation energy is increased beyond to 35 (mu) J/cm2, a second much faster transient is superimposed, and the PL spectrum narrows to a single line, centered at the 0-1 transition of the low energy set of the steady PL spectrum. The width of the emission line is 13 cm-1. These observations are explained in terms of a stimulated emission process.
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Francis Garnier, Gilles Horowitz, Pierre Valat, Faycal Kouki, and Veronique Wintgens "Stimulated emission in sexithiophene single crystals", Proc. SPIE 3145, Optical Probes of Conjugated Polymers, (1 December 1997);

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