Oxygen vacancies in lithium niobate

Optical absorption peaks at 760 and 500 nm in LiNbO3 are assigned to oxygen vacancies containing one and two electrons, respectively. The 500‐nm band appears after annealing above approximately 500 °C in a vacuum, i.e., a reducing atmosphere, and continues to grow with increasing anneal temperature. Optical bleaching near 77 K destroys the band at 500 nm and produces both a band at 760 nm and a Nb4+ electron spin resonance spectrum. The spectral dependence of the bleaching light required to convert the 500‐nm band to the 760‐nm band is determined.