Photosensitive Mechanism of Dopant-Free, Ultraviolet-Sensitive Calcium Aluminate Glasses

Calcium aluminate glasses show high sensitivity to ultraviolet radiation without the doping of optically active components. A mechanism is proposed to account for their photosensitivity on the basis of the result that the cause of UV-induced coloring is the emergence of two kinds of paramagnetic centers, an aluminum-oxygen hole center (Al-OHC) and an ozonide (O^-₃). In this model, a peroxy linkage connecting tetrahedrally coordinated Al³⁺s and a physically dissolved O₂ molecule are assumed to be present in the glasses as structural defects. On exposure to UV rays, the peroxy linkage homolvtically dissociates into a pair of A1-OHC's by absorbing UV quanta and one of the two resulting A1-OHC's combines with a nearby O₂ to form an ozonide. Experimental evidences substantiating the mechanism are also reported.