Photoluminescence spectra from the Si impurity center in diamond films grown by chemical-vapor deposition techniques were studied at temperatures between 9 and 300 K. Laser excitation at 514.5 nm, and resonant with the zero-phonon absorption line at 737 nm (1.6823 eV), were used. Luminescence lines become narrowed at resonance excitation, and the vibrational structure of the Si center was observed with a major phonon replica at 767 nm (1.6165 eV). The observed vibrational energy of 515 cm−1 supports a diatomic quasi-molecular Si2 center structure. Temperature dependencies of the linewidth of the zero-phonon line and its phonon replica were measured and the origins of the broadening are discussed.

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Photoluminescence decay times and quantum yields were measured at 77 K in the spectra of two Si-doped diamond films grown by the chemical-vapor deposition technique. A decay time of 950 ps for both films and a quantum yield of 0.05 for one film were determined for the Si center zero-phonon optical transition at 737 nm ͑1.6823 eV͒. Two broad subbands with decay times of 55 and 650 ps and yields of 8ϫ10 Ϫ4 were observed in the luminescence at 600, 650, and 720 nm and ascribed to an sp 2 nondiamond carbon phase.