Photoluminescence intensity and anisotropy decays in amorphous carbon

The decays of intensity and anisotropy of UV-excited photoluminescence (PL) in hydrogenated amorphous carbon have been investigated in the ps–ns time range. For emission energies Eem between 1.8 and 3.5 eV, anisotropy decreases within 100 ps and reaches a plateau within 1 ns. The emission anisotropy plateau value increases (from 0.02 to 0.12) and the decay time of PL intensity decreases (from 1 ns to 40 ps) as Eem increases. The exponential increase of time-averaged anisotropy as Eem increases is explained by a competition between exciton decay and randomization of polarization due to electronic excitation energy transfer (Förster mechanism) between chromophores.