Electron paramagnetic resonance and electron-nuclear double resonance were used to identify and characterize electrons trapped by oxygen vacancies and holes trapped by lithium vacancies in lithium tetraborate crystals. The study included a crystal with natural abundances of 10B and 11B and a crystal that was highly enriched in 10B. The as-grown crystals contained isolated oxygen vacancies, lithium vacancies, and copper impurities; all in non-paramagnetic charge states. During irradiation at 77K using 60kV X-rays, doubly ionized oxygen vacancies trapped electrons while singly-ionized lithium vacancies and monovalent copper impurities trapped holes. The vacancies returned to their pre-irradiation charge states when the temperature of the sample was increased to approximately 90K. Hyperfine interactions with 10B and 11B nuclei, observed between 13 and 40K in the radiation-induced electron paramagnetic resonance and electron-nuclear double resonance spectra, provided models for the two vacancy-related defects. The electron trapped by an oxygen vacancy was localized primarily on only one of the two neighbouring boron ions while the hole stabilized by a lithium vacancy was localized on a neighbouring oxygen ion with nearly equal interactions with the two boron ions adjacent to the oxygen ion.

Identification of Electron and Hole Traps in Lithium Tetraborate (Li2B4O7) Crystals: Oxygen Vacancies and Lithium Vacancies. M.W.Swinney, J.W.McClory, J.C.Petrosky, S.Yang, A.T.Brant, V.T.Adamiv, Y.V.Burak, P.A.Dowben, L.E.Halliburton: Journal of Applied Physics, 2010, 107[11], 113715