Study on color change of synthetic type Ib diamond crystals treated by high temperature and high pressure annealing

Type Ib diamond crystals, synthesized by using temperature gradient method, were treated by high temperature and high pressure annealing through domestic cubic press, then the samples were tested by colorimeter, and Fourier transform infrared spectrometer.It was found that under the condition of high temperature and high pressure, accompanying by the aggregation of nitrogen atoms, the initial type Ib diamond crystal had experienced a process of color change, which became darker at first, and then faded gradually, until it turned to a colorless type Ia diamond single crystal.