Photoluminescence excitation by band‐gap optical absorption in chemical vapor deposition diamond films

Photoluminescence excitation (PLE) spectra at photon energies near the indirect band gap of diamond have been obtained for diamond films grown by the filament‐assisted chemical vapor deposition (CVD) method. The PLE intensity was observed to increase abruptly with photon energy above 5.5 eV. This increase coincides with the onset of phonon‐emission‐assisted interband absorption, which was observed independently by diffuse transmittance measurements. A lower‐energy PLE threshold at ∼5.25 eV, which coincides approximately with the onset of phonon‐absorption‐assisted interband absorption, was observed in the spectrum of a gem‐quality natural diamond, but not in the spectra of the CVD‐grown films. Emission spectra of the luminescence excited by above‐band‐gap photons have features similar to luminescence spectra of the same specimens excited by 20‐keV electrons. The spectrally integrated intensities of the luminescence excited by above‐band‐gap photons and by electrons were found to vary from specimen to spec...