Evolution And Colouration of Lattice Defects in Diamonds at High Pressure and High Temperature

HPHT in the laboratory provides the lattice defects in a brown yellow diamond with sufficient homogeneously oriented pressure and potential energy that are favorable for the dislocation in types Ⅰa and Ⅱa brown yellow diamonds. Such changes in dislocation finally result in colour transformation from the brown yellow to the colourless, yellow green and blue. The present research shows that the pseudo grid like stress pattern, composed of two groups of discontinuously arranged deformed bands which are fine and dense and rippled, and have alternated brightness and darkness and graded boundary lines, is included in a reconditioned gliding surface (line) system, representing the displacement, reorganization, and disintegration of the dislocation in type Ⅱa diamond. The dislocation walls interphased and regularly arranged in the direction of the tetragonal growth rings of the diamond and the strong deformation bands whose boundaries experienced sudden changes like repeated twin crystals, are both included in the enhanced gliding surface (line) system, representing the multiplication and movement of the dislocation in type Ⅰa diamond.The Raman spectrum peak at 3760cm^-1 (or at 3738cm^-1 at low temperature) and the Raman spectrum bands at 2087cm^-1 and 796cm^-1 result from the crystal lattice defects in types Ⅰa and Ⅱa diamonds. The formation and evolution of the lattice defects are proved to restrain the colouring and luminescence of the diamond.