Diamond photoluminescence spectra: dependence on excitation energy and microstructure

Photoluminescence data are presented for diamond films grown by different techniques (hot-filament CVD, microwave PECVD, DC arc-jet) and excited in the range 450-650nm by different laser sources. In large-grain textured samples, sharp vibronic structures, related to nitrogen and silicon impurity centers, are clearly observed, whereas in small-grain, randomly oriented films spectra are dominated by broad luminescence bands, whose maxima move with excitation energy. In the former case a careful deconvolution of emission spectra allows us to obtain vibronic parameters of the centers and their fine structure details, while excitation spectra give the energy location of higher electronic excited states. On the other hand, the line-shape and the excitation-dependent shift of broad luminescence bands are related to a continuous distribution of gap states, able to trap photogenerated electron-hole pairs. (C) 1998 Elsevier Science S.A.