EPR of hole centers in nonlinear LiBO3 crystals

Results are presented of an EPR study of theO − hole center in LiB 3 O 5 (lithium triborate) crystals. Analysis of angular dependences of EPR spectra is used to determine the principal values of the g tensor ( g XX =2.032, g YY =2.020, g ZZ =2.007), along with the modulus of the isotropic part of the A 2 tensor (| A |=12.2 G) and the orientations of the principal axes of the paramagnetic O − center. The most probable model for the O − center in lithium borate crystals is the following: a hole trapped by the center is localized on a p -orbital of an oxygen ion linking two boron atoms with coordination numbers three and four near a negatively charged stabilizing structural defect. In this case the characteristic hyperfine splitting is due primarily to the interaction of the unpaired electron spin with the 11 B nucleus.