The photoluminescence of several natural and synthetic diamonds of type I and type II has been examined in the spectral range 1.35–1.85 eV (920–670 nm) at 300 and 79 K at ambient pressure. Two emission bands with zero-phonon lines at 1.575 and 1.770 eV are observed in all yellow type-Ia natural diamonds. These bands are attributed to aggregate nitrogen defects and coexist with other known defect emission bands N2 and N3. The implications for high-pressure research using diamond anvils are discussed.

• Received 9 September 1988

DOI:https://doi.org/10.1103/PhysRevB.39.5464