The UV-induced photocoloration of cubic zirconia (c-ZrO₂) stabilized by Y₂O₃, Yb₂O₃ and Er₂O₃ and treated as a wide bandgap metal oxide (MO₂) heavily doped with M³⁺ ions has been examined by diffuse reflectance spectroscopy. Using the narrow f-f absorption bands of optically labeled Yb³⁺ and Er³⁺ as the M³⁺ dopants, the interaction of these dopant ions with photocarriers is demonstrated spectroscopically against a non-resolved broadband background. The latter occurs as a result of an offset of specific f-f absorption bands following conversion of M³⁺ ions into optically silent M²⁺ ions by the trapping of photoelectrons or by a change of the local symmetry of the M³⁺ surroundings caused by the UV-induced formation of color centers.