Electron paramagnetic resonance and electron–nuclear double resonance were used to characterize four Ti3+ centers in undoped crystals. These 3d1 defects (S = ½) were produced by ionizing radiation (60kV X-rays or 355nm photons from a tripled Nd:YAG laser), and formed when the regular Ti4+ ions in the crystal trap an electron. Two of these trapped-electron centers were only observed in hydrothermally grown material and the other 2 were predominant in flux-grown material. Both of the Ti3+ centers in hydrothermally grown crystals had a neighboring proton (i.e. an OH- molecule). In the flux-grown crystals, one of the Ti3+ centers was adjacent to an O vacancy and the other center was tentatively attributed to a self-trapped electron (i.e. a Ti3+ center with no stabilizing entity nearby). The g matrix and P hyperfine matrices were determined for all four Ti3+ centers, and the proton hyperfine matrix was determined for the 2 centers associated with OH- ions. These Ti3+ centers contribute to the formation of the gray tracks often observed in KTP crystals used to generate the second harmonic of high-power, near-infrared lasers.

Electron Paramagnetic Resonance and Electron–Nuclear Double-Resonance Study of Ti3+ Centers in KTiOPO4. S.D.Setzler, K.T.Stevens, N.C.Fernelius, M.P.Scripsick, G.J.Edwards, L.E.Halliburton: Journal of Physics - Condensed Matter, 2003, 15[23], 3969-84