Observation of the H2 defect in gem-quality type Ia diamond

The H2 defect with its zero-phonon line at 986.1 nm (1.257 eV, 10141 cm(-1) ) was first described in 1956 and characterized in detail in 1990-91. In th is paper, the observation of strong H2 bands in greenish-yellow natural typ e Ia gem-quality diamonds is reported. These 'H2 diamonds' were apparently subjected to a treatment possibly involving irradiation and clearly involvi ng high temperature annealing. Besides burns on the surface and in fracture s, they typically showed strong green luminescence associated with brownish -yellow graining, strong H3/H4 bands, weak to strong H2 bands, and no H1b/H 1c lines. Some stones displayed a weak 637 nm line as well. A model explain ing the formation of the 1-12 defect in type Ia diamond is proposed based o n the stability and interaction of defects in diamond as a function of temp erature and time. (C) 1999 Published by Elsevier Science S.A. All rights re served.