Multi-band structure of amorphous carbon luminescence

Structured photoluminescence (PL) spectra of hydrogenated amorphous carbon (a-C:H) layers prepared from benzene are presented. The spectra contain bands with peak positions in the range of 4.34-4.50, 3.93-4.01 and 3.64-3.79 eV in the ultraviolet region, and additional luminescence bands are in the energy regions of 3.19-3.28 and 2.85-2.96 eV, besides the previously mostly measured band, with a peak in the 2.28-2.48 eV photon energy range. Relative efficiency of these bands depends on the deposition conditions. Each of the new bands could be excited above a given photon energy and, therefore, the overall spectral shape as well as the structured feature of a-C:H luminescence varies with excitation energy. It is supposed that the opening of new radiation recombination transitions with increasing excitation energy explains the appearance of new luminescence bands. (C) 2002 Elsevier Science B.V. All rights reserved.