Defects responsible for gray tracks in flux-grown KTiOPO4

Abstract

Electron paramagnetic resonance (EPR) has been used to identify the primary electron and hole traps responsible for ‘‘gray tracks’’ in flux-grown KTiOPO4(KTP). Ionizing radiation (x rays) was used to produce the gray-track effect. During an irradiation at 0 °C, a broad absorption band peaking near 500 nm is introduced, the EPR spectra from a series of Ti3+ centers appear, and the dominant EPR spectrum associated with Fe3+ ions decreases significantly. Following the irradiation, the decay of the optical absorption and the Ti3+ centers, along with the growth of Fe3+ centers, were monitored over a period of 20 h at room temperature. Changes in the EPR spectra of the Ti3+ and Fe3+ centers during the anneal correlated with the decay of the induced optical absorption (i.e., gray track). These results demonstrate that Fe3+ centers are the primary hole trap and Ti4+-VO complexes are the primary electron trap responsible for gray track formation in flux-grown KTP crystals.

DEPSCOR-95: Development of Nonlinear Optical Materials for Optical Parametric Oscillator and Frequency Conversion Applications in the Near- and Mid-Infrared

“…24 ' 26 It has many excellent optical and physical properties and is presently used in second harmonic generation (SHG) and optical parametric oscillator (OPO) devices. However, laser-induced damage [27][28][29][30][31][32] continues to be a problem in some of these applications. Gray tracks, regions of increased visible absorption, may form along the beam path in the bulk of a KTP crystal when the pump laser operates at high peak power.…”

“…The EPR spectrum reveals hyperfine interaction with three 100% abundant I = Vi nuclei and the ENDOR spectrum shows that two of these interactions are with phosphorus nuclei while one is with a proton. Both of the interactions that are attributable to phosphorus are separated by twice v N for 31 Figure 31 shows the EPR spectrum of this center taken with the magnetic field along the a axis and reveals hyperfine interactions with three 100% abundant I = Vi nuclei, strikingly similar to the spectrum for II hyd . The identity of the neighboring nuclei can not be verified since there is no ENDOR data for this center.…”

“…Figure 29 shows the EPR and ENDOR spectra of this center taken with the magnetic field along the a axis. The EPR spectrum shows four 100% abundant I = 14 hyperfine interactions, and the ENDOR spectrum reveals that three of these interactions are with 31 Table VIII. Principal values and directions of the g and A matrices for the I hyd Ti 3+ center in hydrothermal grown KTP.…”

“…This allows a few of the electrons and holes to become stabilized at widely separated sites in the crystal and form the point defects that contribute to the induced visible optical absorption (i.e., gray tracking). In general, holes will be trapped at transition-metal ions, 31 such as Fe and Cr, or they will be localized on oxygen ions adjacent to stabilizing entities such as potassium vacancies 34 other EPR signals appear. Of the new EPR spectra induced by the x-rays or the laser beam, we find that some can be monitored at room temperature while others can only be seen at lower temperatures.…”

Gamma irradiation-induced absorption in single-domain and periodically-poled KTiOPO_4 and Rb:KTiOPO_4

“…Blue and green -light induced infrared absorption have been studied before in KTP, Rb:KTP as well as PPKTP and PPRKTP [23][24][25][26][27]. The color centers which are responsible for near-infrared absorption in KTP isomorphs are related to polarons formed by self-trapped photo-generated electrons and holes in proximity to Ti 4+ and O 2-ions, respectively [27][28][29].…”