EPR and ENDOR study of an oxygen-vacancy-associated Ti3+ center in RbTiOPO4 crystals

The dominant Ti3+ trapped electron center in flux-grown RbTiOPO4 (RTP) crystals has been characterized using electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR). This center is produced during an X-ray irradiation at room temperature when a Ti4+ ion traps an electron and becomes a Ti3+ ion, and is best studied in the 30–40 K range. The EPR spectrum contains a three-line hyperfine pattern from two nearly equivalent neighboring 31P nuclei, along with hyperfine lines from the 47Ti and 49Ti nuclei. The g matrix, determined from the angular dependence of the EPR spectrum, has principal values of 1.819, 1.889, and 1.947. Hyperfine matrices for four 31P nuclei are obtained from the angular dependence of the ENDOR spectrum. The proposed model for this defect is a Ti3+ ion adjacent to an oxygen vacancy at an OT position. Analogies are made to a similar Ti3+ center in KTiOPO4 (KTP) crystals.