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 E-em between 1.8 and 3.5 eV, anisotropy decrea ses within 100 ps and reaches a plateau within 1 ns. The emission anisotrop y plateau value increases (from 0.02 to 0.12) and the decay time of PL inte nsity decreases (from 1 ns to 40 ps) as E-em increases. The exponential inc rease of time-averaged anisotropy as E-em increases is explained by a compe tition between exciton decay and randomization of polarization due to elect ronic excitation energy transfer (Forster mechanism) between chromophores. (C) 2000 Elsevier Science B.V. All rights reserved.