AN OSCILLATING VISIBLE-LIGHT OPTICAL-CENTER IN SOME NATURAL GREEN TO YELLOW DIAMONDS

Visible spectra taken at 72 K of a group of ten green-to-yellow-colore d natural gem-quality diamonds show more than 30 sharp absorption band s between 13140 and 18420 cm(-1) (1.63 and 2.28 eV), suggesting one or two defects that oscillate to visible light, a phenomenon not previou sly reported for diamond. Preliminary analysis of these spectra shows two oscillations, one dominating the lower energy end of this range wi th an energy spacing of 0.021 eV, and another appearing at the higher energy end of the range with a spacing of 0.025 eV. All samples show w eak to moderate strength infrared absorptions typical of hydrogen, and of single substitutional nitrogen. The green color in nine of these d iamonds is caused by the broad overlap at the base of these many absor ption bands, not by a GR1 center, and thus forms a new cause of natura lly occurring green color in diamond. Similar ''many-banded'' features have been observed by others in the low temperature cathodoluminescen ce spectra of diamond and in the low temperature luminescence spectra of minerals containing a molecular ion; perhaps the hydrogen or nitrog en (or both) play a role in causing these oscillations. (C) 1998 Publi shed by Elsevier Science S.A.