Inverse correlation between the intensity of luminescence excited by electrons and by visible light in chemical-vapor-deposited diamond films

Diamond films grown by filament-assisted or microwave-plasma-assisted chemical-vapor deposition (CVD) were characterized by photoluminescence (PL), cathodoluminescence (CL), and Raman spectroscopies. The laser-excited PL spectra of these films in and near the carbon Raman region (1100–1800 ${\mathrm{cm}}^{\mathrm{-}1}$ from the 514.5-nm laser line, or 2.18–2.28 eV) are broad and featureless; CL spectra measured within a wider spectral range (1.5–3.5 eV) show several distinct components. Because of its correlation with the Raman band of ${\mathit{sp}}^2$-bonded carbon, the visible-laser-excited PL in the carbon Raman region is attributed to ${\mathit{sp}}^2$-bonded carbon clusters. The spectrally integrated CL intensity is found to vary from specimen to specimen approximately inversely with the intensity of the laser-excited PL. This inverse correlation is especially strong for one component of the CL, a broad band at 2.85 eV. To explain these results, it is proposed that the luminescence centers in these CVD diamond films can be classified into two types with differing excitation and recombination properties. Rate equations are derived for the luminescence kinetics of such a system of two types of recombination centers.