Surface photochemical processes and the interconnected photophysical events taking place in the bulk and at the surface of a wide band gap insulator material, e.g. scandia (Sc₂O₃), have been examined to ascertain the role of intrinsic defects (e.g. anion and cation vacancies) on surface processes such as photoadsorption of electron acceptor (O₂) and donor (H₂ and CO) molecules. The influence of surface processes on the formation and destruction of photoinduced defects (i.e. electron F-type color centers and hole V-type color centers) in scandia and the role that color defect centers play in the overall efficiency of surface reactions have been explored spectroscopically. Photoadsorption of gases on the scandia particle surface and the resulting effect on photocoloration and photobleaching have been used to identify the type of color centers produced on photoexcitation with UV light in the fundamental absorption edge (intrinsic) and in the extrinsic absorption region of powdered scandia specimens. Formation of color centers red-shifts the spectral limits of surface photoreactions. Formation of F and V color centers decreases the quantum yield of surface photochemical processes because of recombination of charge carriers through color centers, but increases the overall efficiency of these processes through photobleaching of the color centers on irradiation at appropriate UV wavelengths.