Defect photoluminescence in polycrystalline diamond films grown by arc-jet chemical-vapor deposition

We have studied a series of sharp photoluminescence emission lines between 1.65 and 1.80 eV in synthetic diamond films. The series of lines is decomposed into a set of parent lines plus vibrational sidebands spaced 24 meV apart. This energy does not correspond to any phonons with high density of states in the diamond crystal. The relative intensities of the main lines exhibit no temperature dependence (between 20 and 160 K), implying ground-state splitting. The narrow linewidth and temperature-independent emission energy imply only weak interaction with the diamond host. The temperature-dependence of the linewidth is well described by thermal broadening. We attribute the emission to optical centers as a consequence of tungsten incorporation into the diamond film. The tungsten originates from the electrode during deposition.