Identification of electron and hole traps in lithium tetraborate (Li2B4O7) crystals: Oxygen vacancies and lithium vacancies

Authors

M. W. Swinney, Air Force Institute of Technology
J. W. McClory, Air Force Institute of TechnologyFollow
J. C. Petrosky, Air Force Institute of Technology
Shan Yang (杨山), West Virginia University
A. T. Brant, West Virginia University
V. T. Adamiv, Institute of Physical Optics, Ukraine
Ya. V. Burak, Institute of Physical Optics, Ukraine
P. A. Dowben, University of Nebraska-LincolnFollow
L. E. Halliburton, West Virginia University

Date of this Version

2010

Citation

JOURNAL OF APPLIED PHYSICS 107, 113715 (2010)

Comments

© 2010 American Institute of Physics

doi:10.1063/1.3392802

Abstract

Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) are used to identify and characterize electrons trapped by oxygen vacancies and holes trapped by lithium vacancies in lithium tetraborate (Li₂B₄O₇) crystals. Our study includes a crystal with the natural abundances of ¹⁰B and ¹¹B and a crystal highly enriched with ¹⁰B. The as-grown crystals contain isolated oxygen vacancies, lithium vacancies, and copper impurities, all in nonparamagnetic charge states. During an irradiation at 77 K with 60 kV x-rays, doubly ionized oxygen vacancies trap electrons while singly ionized lithium vacancies and monovalent copper impurities trap holes. The vacancies return to their preirradiation charge states when the temperature of the sample is increased to approximately 90 K. Hyperfine interactions with ¹⁰B and ¹¹B nuclei, observed between 13 and 40 K in the radiation-induced EPR and ENDOR spectra, provide models for the two vacancy-related defects. The electron trapped by an oxygen vacancy is localized primarily on only one of the two neighboring boron ions while the hole stabilized by a lithium vacancy is localized on a neighboring oxygen ion with nearly equal interactions with the two boron ions adjacent to the oxygen ion.