Line width study in fluorescence excitation spectra of single pentacene molecules introduced as impurities in p-terphenyl crystal

Abstract

We report results on line widths in the fluorescenceexcitation spectra of single pentacene molecules inp-terphenyl crystal flakes for the 01 and 02 sites at 1.85 K. A setup for the measurement of fluorescence excitation spectra of single impurity molecules with an overall quantum efficiency of about 0.1% has been designed. Spectra obtained with a signal-to-noise ratio up to 1O:l were recorded at different laser excitation intensities in the range from 1 to 5 mW/cm2. The line widths measured for different pentacene impurity molecules and extrapolated to zero probing intensity show remarkable variation in the range from 5 to 15 MHz. A reason why some lines are narrower than the lifetime-limited one (8 MHz) is discussed.