BACKGROUNDIn order to quickly identify and screen high pressure and high temperature (HPHT) grown synthetic diamonds, a lot of research about their luminescent and spectral characteristics has been done. However, the comparative analysis is lacking, and less attention is paid to electrical and magnetic properties.

OBJECTIVESTo summarize the spectral characteristics and investigate the electrical and magnetic properties of HPHT synthetic diamonds systematically.

METHODSConventional gemological observation, high precision spectroscopy and electrical conductivity and magnetism testing were used for comparative analysis of 49 colorless and yellow samples.

RESULTSThe residual metal catalysts, including iron, cobalt, and nickel, caused the ferromagnetism of diamonds. All of the HPHT synthetic diamond samples could be attracted by the magnetic bar with magnetic intensity up to 12000Gs. The colorless samples were type Ⅱa+Ⅱb diamonds. The presence of boron led to its good conductivity, and the conductivity increased with increased boron content. The yellow samples were Ib+IaA type diamonds, and about one-third of the single nitrogen was converted into A aggregate. The synthetic diamond had undergone high temperature annealing treatment after growth. The ubiquitous presence of boron, and the presence of nitrogen mainly as single atoms and A aggregates led to the characteristic infrared spectra of HPHT synthetic diamonds. HPHT synthetic diamonds often contained crystal lattice defects caused by impurity elements such as nitrogen, nickel and silicon, which led to characteristic photoluminescence spectra. Colorless samples showed strong blue-green fluorescence and phosphorescence, whereas yellow samples had green fluorescence, with obvious cube-octahedron patterns.

CONCLUSIONSSpectral and luminescent characteristics are still an important basis for screening and identification of HPHT synthetic diamonds. HPHT synthetic diamonds under the current growth technology also have obvious differences from natural diamonds in both conductivity and magnetism, which can be used as an auxiliary basis for rapid identification.