We have developed a method called optical transient positron spectroscopy and apply it to study the optically induced carrier trapping and charge transfer processes in natural brown type IIa diamond. By measuring the positron lifetime with continuous and pulsed illumination, we present an estimate of the optical absorption cross section of the vacancy clusters causing the brown color. The vacancy clusters accept electrons from the valence band in the absorption process, giving rise to photoconductivity.
Mäki, J-M., Tuomisto, F., Varpula, M., Fisher, D., Khan, R. U. A., & Martineau, P. M. (2011). Time dependence of charge transfer processes in diamond studied with positrons. Physical Review Letters, 107(21), 1-5. . https://doi.org/10.1103/PhysRevLett.107.217403