Abstract
Naturally occurring pink diamonds include defect centers with properties that differ greatly from those of commonly synthesized diamond centers. The pink diamond color-center demonstrates optically-controllable photochromism which is stable at ambient temperatures. The nature of this defect and the origin of the photochromism are yet to be explained. In this work we show that the photochromic behavior can be explained by competing photoionization processes at multiple defect centers in response to an applied optical pump. Our approach quantitatively explains the dependence of both the response rate and the resulting color on the pump wavelength. From measurements of the photochromic response we are able to extract parameters that describe the ionization cross-sections of the involved centers.