Diamond luminescence - resolved donor-acceptor pair recombination lines.

Cathodoluminescence and photoluminescence were analysed in diamond films prepared by microwave plasma assisted chemical vapour desposition. Results are presented for various diamond films differing in doping and crystalline structure. In the energy range 2.67 - 2.07 eV, a series of 13 sharp luminescence lines was observed at temperatures below 200 K. In a tentative interpretation this 2.67 eV system is attributed to donor-acceptor pair recombination. The Coulomb energy depends on the discrete values for the pair separation in the expected manner, including a Bohr radius correction for the three closest pairs. Likely candidates for the pairs are the nitrogen donor and the boron acceptor. The presence of nitrogen is evident from the luminescence of the 2.16, 2.81 and 3.19 eV nitrogen centres. Boron is present by doping or contamination. Vibronic sidebands from the nearest neighbour pair were observed and analysed. Characteristic local vibrational mode frequencies of nitrogen and the boro n isotopes are found, providing further support for the proposed model.