  Single-nanotube photometry was used to measure the product of absorption
cross-section and fluorescence quantum yield for 12 (n,m) structural species of
semiconducting SWNTs in aqueous SDBS suspension. These products ranged from 1.7
to 4.5 x 10(-19) cm2/C atom, generally increasing with optical band gap as
described by the energy gap law. The findings suggest fluorescent quantum
yields of ~8% for the brightest, (10,2) species and introduce the empirical
calibration factors needed to deduce quantitative (n,m) distributions from bulk
fluorimetric intensities.
