Photoluminescence vibrational structure of Si center in chemical-vapor deposited diamond

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.