Single perylene molecules in the Shpol'skii matrix n-nonane have been
investigated at 1.7 K using a frequency-doubled cw Ti:sapphire laser a
s an excitation source. Fluorescence excitation spectra within the inh
omogeneously broadened 0-0 absorption band around 443.8 nm were taken.
The combination of high fluorescence quantum yield and low intersyste
m crossing rate with a relatively short-lived triplet state allowed th
e direct observation of fluorescence photon bunches. The time distribu
tion of the resulting emission gaps for the specific single molecule s
tudied in detail leads to a triplet lifetime of tau(p) = 1.1 +/- 0.5 m
s.