Identification of Ti3+ in potassium titanyl phosphate and its possible role in laser damage

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Abstract
Four related Ti3+ centers in potassium titanyl phosphate (KTiOPO4 or KTP) may be created with either application of dc electric fields or with hydrogen at 800 °C. Single‐crystal electron paramagnetic resonance allows determination of the g tensors of the four centers. Hyperfine coupling is observed with one47,49 Ti and two (nearly) equivalent 31P. The most abundant center is characterized by gx=1.7709(5), gy=1.8723(5), gz=1.9462(5), principal values of ‖ATi‖ of 80, 33, and 24 MHz, and axially symmetric AP’s with principal values of 16.3 and 21.8 MHz. Optical absorption centered at 13 000–18 000 cm−1 is quite broad, relatively strong, and approximately twice as intense for light whose electric vector is polarized parallel to c as it is for a or b. A charge transfer mechanism in addition to d−d transitions may account for the absorption. Ti3+ is much more difficult to produce in hydrothermally grown KTP than in flux‐grown KTP, a difference ascribed to the presence of oxygen vacancies or interstitial potassium in the latter. Similarities in the energy and polarization of optical absorption suggest that coloration induced by laser damage is due also to Ti3+.

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