Photoluminescence excitation (PLE) spectra, measured at varying temperature
s and for different luminescent energies, are applied systematically to the
study of defects in Ia, Ib, IIb, and chemical-vapor-deposired (CVD) diamon
d. It is shown that the green luminescent band in CVD diamond films consist
s 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 recombinati
on. The phatoionization threshold for transitions from the valence band to
the donor level is determined as 3.25 eV. Based on PLE measurements the bro
ad blue band is assigned to the vibronic band of a dislocation-related cent
er with the ground state position in the range from E-V to E-V + 0.37 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 spectr
a from CVD diamond is used to deduce E-C - 2.24 eV and E-C - 2.05 eV as the
optical ionization thresholds to the conduction band for the divacancy-rel
ated and the 1.68 eV centers, respectively.