Electron paramagnetic resonance (EPR) has been used to investigate an acceptor in as-grown single crystals of ZnGeP2. The spectra are characterized by equally spaced triplets with 1:2:1 intensity ratios representing hyperfine interactions (varying from 35 to 55 G in magnitude) with two equivalent phosphorous nuclei. Their angular dependence shows that there are four crystallographically equivalent orientations of the defect. The principal values of the g matrix are 2.002, 2.021, and 2.074 and the corresponding principal axes, at one of the four sites, are the [011], [1̄00], and [01̄1] directions, respectively. Two possible models are suggested for this acceptor: Either a zinc vacancy (VZn) or a zinc ion on a germanium site (ZnGe). It also is suggested that the acceptor responsible for the EPR signal is the same acceptor, namely AL1, that gives rise to a dominant near-infrared absorption band.

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.

An electron-nuclear double resonance study of the lowest triplet state of pyrazine J. Chem. Phys. 97, 110 (1992); 10.1063/1.463609An electron-nuclear double resonance study of the lowest triplet state of pyrimidine

Electron paramagnetic resonance (EPR), electron-nuclear double resonance, optical absorption, and thermoluminescence have been used to investigate radiation-induced point defects in a single crystal of lithium triborate (LiB3O5). Two prominent defects are observed after irradiation near liquid-nitrogen temperature with 60 kV x rays. A four-line EPR spectrum, with 12.2 G splittings, is assigned to a trapped-hole center, and another four-line EPR spectrum, with 120 G splittings, is assigned to a trapped-electron center. In each case, the nucleus responsible for the observed hyperfine is 11B. The trapped hole is localized on an oxygen ion and has a weak hyperfine interaction with one neighboring boron nucleus, whereas the trapped electron is localized primarily on a boron ion with a correspondingly larger hyperfine interaction. Both defects become thermally unstable near 125 K, and their decay (i.e., recombination) correlates with an intense thermoluminescence peak at this same temperature. An optical absorption peak at 300 nm is produced by the x rays and thermally decays at the same temperatures as the EPR spectra.

A series of Ti3+ centers have been formed in hydrothermally grown and flux-grown potassium titanyl phosphate (KTiOPO4 or KTP). These 3d1 defects (S=1/2) were created with 60 kV x rays at 77 K, and electron paramagnetic resonance and electron-nuclear double-resonance (ENDOR) data were taken below 30 K. The ENDOR spectra show that the two Ti3+ centers having the largest concentrations in hydrothermally grown KTP have a neighboring proton, presumably in the form of an adjacent OH− ion. In contrast, ENDOR spectra show that neither of the two Ti3+ centers having the largest concentrations in flux-grown KTP have a neighboring proton. These significant differences in the local environment of the Ti3+ centers may help explain why KTP crystals have shown differing susceptibilities to gray tracking.