ELECTRON-PARAMAGNETIC RESONANCE STUDY OF PARAMAGNETIC DEFECT CENTERS FE-3+ AND CR-3+ IN KTIOPO4

An EPR study of Fe3+ centres in single crystals of KTiOPO4 (KTP) has been performed. Two crystals grown under identical conditions have been used in the experiment carried out at the Q-band frequency: the first was iron doped and the other was undoped. Four Fe3+ centres have been observed. All spin-Hamiltonian parameters were calculated for the four centres. Comparison of the pseudosymmetries obtained from fourth-order constants of the spin Hamiltonian and from a fourth-order crystal-field calculation for the two Ti octahedra allowed us to locate two Fe3+ centres at each Ti site in KTP. The absence of a strong axial deviation from cubic symmetry shows that the charge compensation mechanism is not at short distance for the four centres. All four cenres denoted as ST1, ST2, ST3 and ST4 are present in the iron-doped crystal but only one (ST4) is observable in the undoped crystal. In the undoped crystal, also Cr3+ was observed. Results for the Cr3+ centres are given and compared with those already reported by Hasanova and co-workers.