Hyperfîne structure associated with the dominant radiation-induced trapped hole center in RbTiOPO₄ crystals

Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) have been used to characterize the complex hyperfme patterns exhibited by the primary radiation-induced trapped hole center in single crystals of RbTiOPO₄ (commonly referred to as RTF). These defects are produced at 77 K by irradiating with X-rays, and they are destroyed by raising the temperature above approximately 170 K. In this center, the hole resides on a bridging oxygen ion located between two titanium ions and is stabilized by a nearby rubidium vacancy. Hyperfme splittings from interactions with one rubidium neighbor and one phosphorus neighbor are resolved in the EPR spectra. The ENDOR spectra show one larger phosphorus interaction and four smaller phosphorus interactions. Principal values and principal axis directions for this larger phosphorus interaction are obtained from the ENDOR angular dependence.