The infra-red absorption by diamond and its significance

4. Summary

The non-luminescent diamonds exhibit the infra-red absorption spectra of the second and third orders, while the first order is totally absent. A critical examination of the spectrographic records shows clearly that the second-order spectrum is based on the same vibrational modes with discrete frequencies as the first, the activities of the modes, however, being different in the two cases.

The non-luminescent diamonds exhibit a type of birefringence which arises from the presence in them of laminations orientated parallel to the octahedral planes or to the dodecahedral planes of the crystals or to both.