Luminescence excitation spectra in diamond

Photoluminescence excitation (PLE) spectra, measured at varying temperatures and for different luminescent energies, are applied systematically to the study of defects in $\mathrm{I}a,$ $\mathrm{I}b,$ $\mathrm{II}b,$ and chemical-vapor-deposited (CVD) diamond. It is shown that the green luminescent band in CVD diamond films consists of two distinct components. The first one is attributed to recombination in the amorphous carbon phase. The second component increases with surface hydrogenation in CVD films, but an analogous band remains almost unchanged in Ib diamond. This band is ascribed to the donor-acceptor pair recombination. The photoionization threshold for transitions from the valence band to the donor level is determined as 3.25 eV. Based on PLE measurements the broad blue band is assigned to the vibronic band of a dislocation-related center with the ground state position in the range from $E_V$ to $E_V+0.37\mathrm{}$ eV. A series of undocumented photoluminescence (PL) lines at 1.81, 1.84, 1.91, 2.02, 2.1, and 2.2 eV is characterized by PL and PLE techniques as belonging to radiative transitions from different excited states to the same ground state of a divacancy-related center. Oscillatory behavior in the PLE spectra from CVD diamond is used to deduce $E_C-2.24\hspace{0.5em}\mathrm{eV}$ and $E_C-2.05\hspace{0.5em}\mathrm{eV}$ as the optical ionization thresholds to the conduction band for the divacancy-related and the 1.68 eV centers, respectively.