Temperature dependent optical emission efficiency in vacuum sublimed alpha-sexithienyl thin films

The photoluminescence spectra and quantum yield of alpha -sexithienyl (T-6) thin films grown in high vacuum have been measured at different temperatur es in the range 30K-300K. The measurements have been performed with a home- built experimental apparatus based on an integrating sphere, which allows l uminescence spectra and quantum yield measurements in the temperature range 5K - 400K. The analysis of the photoluminescence spectra allows to identif y the spectral contribution from molecular aggregates and excitons at each temperature. The quantum yield of the molecular aggregates placed below the exciton band span from 0.1% to 5% in the temperature range 300K - 30K. In the same temperature range, the quantum efficiency of the intrinsic exciton s increases by a factor of two from 0.4% to 1%. Thus we reconcile the multi tude of photoluminescence spectra and quantum yield values previously repor ted for T-6 films grown in different conditions and therefore containing di fferent concentration of aggregate states.