Electron-paramagnetic-resonance (EPR) and electron-nuclear double-reso
nance (ENDOR) techniques have been used to determine the structure of
a radiation-induced trapped-hole center in potassium titanyl phosphate
(KTiOPO4 or KTP). A single crystal of KTP was irradiated with 60-kV x
rays at 77 K to produce the S = 1/2 hole center. Data were then taken
near 30 K. Spin-Hamiltonian parameters describing the g matrix and th
ree P-31 hyperfine matrices were obtained from the angular dependence
of the EPR and ENDOR spectra, respectively. The principal values of th
e g matrix are 2.0008, 2.0250, and 2.0422 and the principal values of
the largest phosphorus interaction are -6.809, -8.125, and -3.848 MHz.
An analysis of the spin-Hamiltonian matrices (i.e., the magnitudes of
their principal values and the directions of their principal axes) le
ads to a model wherein the hole is localized on a bridging oxygen ion
between two titanium ions. The hole is stabilized at this site by a ne
arest-neighbor potassium vacancy. This defect is observed in both hydr
othermally grown and flux-grown KTP, and it is stable only up to appro
ximately 160 K.