APHT treatment of brown type Ia natural diamonds: Dislocation movement or vacancy cluster destruction?

Experimental results of APHT (atmospheric pressure high temperature) treatment of dark brown type Ia natural diamonds are discussed. The APHT treatment was carried out under the atmospheric pressure using an experimental homemade system. The samples were placed in the inert gas current and subjected to 5 or 6 repeated thermal shocks, i.e. the diamonds were sharply heated to 1300–2100 °C. As a result, the original brown color of the samples was considerably reduced. The IR absorption intensity of the main A and B nitrogen centers was not observed to change. However, photoluminescence due to N3 and H3 centers was observed in the treated samples.