Halliday, D., Ulrici, W., & Eaves, L. (1986). Optically induced changes of the Cr-related absorption lines in GaP:Cr-evidence for internal transitions of CrtGa³⁺. Journal of physics. C. Solid state physics, 19, L683-L687. https://doi.org/10.1088/0022-3719/19/29/003