High-resolution optical spectra of the GR defect in diamond

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Abstract
High-resolution absorption and photoluminescence measurements have been carried out on the GR1 zero phonon lines, and absorption measurements on the GR2-8 lines. These transitions are all believed to occur at the GR defect which is created by radiation damage. Carefully selected and annealed natural semiconducting diamonds have been used to minimise line broadening effects due to impurities or lattice strain. The line widths observed at 10K are believed to be close to the intrinsic values. The 1.665 eV line which is due to an A to T transition at the GR1 centre is almost three times as wide as the line at 1.673 eV associated with the E to T transition. This finding is consistent with theoretical models which propose that the A state is a vibronic level derived from the E electronic state. There is, however, no evidence for higher vibronic levels. The linewidths of the GR2-7 transitions are not inconsistent with the recently proposed two-electron model of the GR defect, but this scheme will need to be modified to account for the GR8 lines. There is some evidence, however, which suggests that the lines labelled GR8 may not be associated with the GR defect.

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