Size of spatial confinement at luminescence centers determined from resonant excitation bands of a-C:H photoluminescence

The photoluminescence (PL) emission and excitation spectra of hydrogenated amorphous carbon (a-C:H) were analyzed. The emission spectrum was experimentally deconvoluted for three bands in the green region (2.26 eV, 2.48 eV, 2.67 eV). The luminescence excitation spectrum of these emission bands shows two bands structures and a resonance feature. The spatially localized electron hole pairs are responsible for this resonance excitation feature. Combining these results with those of ellipsometry measurements concerning the optical band gap, the length of the spatially confined electron hole pair localization was calculated. We found that this length varies with the energy of the PL emission. With increasing emission energy the size of the localization changes from 1.15 nm to 0.94 nm.