Mechanism of hydrogen treatment in KTiOPO₄ crystals at high temperature: experimental and first-principles studies

Abstract

The mechanism of coloration and oxygen vacancy formation in KTP crystals treated by hydrogen annealing was systematically investigated.

Evaluation of Electroelastic Properties of YCOB and GdCOB Crystals Irradiated by 6 MeV Xe23+ Ions

“…A similar result is obtained for the GdCOB crystal, where the transmittance of the pristine crystal sample was 90% and then decreased to 83% under the same irradiation conditions. The increased absorption is considered to be associated with the formation of crystal defects (such as oxygen vacancies as reported in refs and ) induced by the Xe 23+ bombardment.…”

Potassium titanyl phosphate (KTP) quasiparticle energies and optical response

“…Even larger is the range of the computationally predicted band gaps. Density-functional theory (DFT) calculations predict values-depending on the choice of the exchange-correlation functional-of 3.0 [18], 3.1 [13,19], 3.3 and 4.0 eV [20], whereas early empirical tight-binding calculations obtained a value of 4.9 eV [21]. Both the measured and the calculated values must be taken with caution: on the one hand, the measured values are concluded from optical experiments and are, therefore, affected substantially by electron-hole attraction effects in contrast to the transport band gap, i.e.…”

Oxygen and potassium vacancies in KTP calculated from first principles

“…The O atoms can be classified according to their coordination: following the notation in [6], oxygen atoms bonded to Ti and P are denoted here O(1)-O(8), while O (9) and O (10) are bonded to two Ti atoms.…”

“…The usage of KTP is affected by the so-called gray tracking, i.e. photochromic damage [5] caused by highintensity laser irradiation [7], electric fields [8] or the exposition in a hydrogen atmosphere at high temperatures [6]. Microscopically, the reduction of Ti atoms has been suggested to cause gray tracking: electron paramagnetic resonance (EPR) signatures assigned to Ti 3+ in intrinsic defect centers were detected in crystals affected by gray tracks [8].…”

“…Microscopically, the reduction of Ti atoms has been suggested to cause gray tracking: electron paramagnetic resonance (EPR) signatures assigned to Ti 3+ in intrinsic defect centers were detected in crystals affected by gray tracks [8]. The transformation of Ti 4+ to Ti 3+ ions has been proposed to result from charge balance conservation after oxygen vacancy formation [6,9]. Subsequent to optical excitation, the photoelectrons are assumed to be trapped by Ti atoms near an O vacancy [8], while photoholes may be captured by Ti-Ti bonded O atoms near a K vacancy [10].…”