Electron paramagnetic resonance and electron–nuclear double-resonance study of Ti3+ centres in KTiOPO4

Abstract

Electron paramagnetic resonance and electron–nuclear doubleresonance have been used to characterize four Ti3+centres in undoped crystals of potassium titanyl phosphate (KTiOPO4 or KTP).These 3d1defects (S = 1/2)are produced by ionizing radiation (either 60 kV x-rays or 355 nm photons from atripled Nd:YAG laser), and form when the regular Ti4+ions in the crystal trap an electron. Two of these trapped-electroncentres are only observed in hydrothermally grown KTP and the othertwo are dominant in flux-grown KTP. Both of the Ti3+ centresin hydrothermally grown crystals have a neighbouring proton (i.e. an OH−molecule). In the flux-grown crystals, one of the Ti3+centres is adjacent to an oxygen vacancy and the other centre istentatively attributed to a self-trapped electron (i.e. a Ti3+centre with no stabilizing entity nearby). Theg matrixand phosphorus hyperfine matrices are determined for all four Ti3+ centres, andthe proton hyperfine matrix is determined for the two centres associated with OH− ions. TheseTi3+centres contribute to the formation of the grey tracks often observed in KTPcrystals used to generate the second harmonic of high-power, near-infrared lasers.