Electron-paramagnetic-resonance study of rhodium impurity ions inKTiOPO4single crystals

An electron-paramagnetic-resonance (EPR) investigation at 90 K of rhodium impurities in thermally reduced KTP crystals is reported. The EPR spectra are assigned to two rhodium centers. It is proposed that the corresponding defects are ${\mathrm{Rh}}^{2+}$ ions substituting for titanium in the two Ti sites of the KTP structure. The spin-Hamiltonian parameters are analyzed and the possible mechanisms accounting for the distortion around the impurity are discussed. Reducing thermal treatments in vacuum of KTP crystals induce a strong increase of the observed EPR spectra, indicating that most rhodium impurities enter in KTP as ${\mathrm{Rh}}^{3+}$ ions.