Point defects in Mg‐doped lithium niobate

Optical absorption, electron spin resonance (ESR), thermoluminescence, and x‐ray‐induced luminescence techniques have been used to characterize point defects in LiNbO3. A series of crystals with different magnesium‐doping levels and Li/Nb ratios were investigated, and the defects were introduced either by x‐ray irradiation at low temperatures (10–85 K) or by reduction at high temperature in a vacuum. The samples may be classified into two groups, according to their response to radiation and reduction. A threshold (i.e., a sharp change in behavior due to a small change in composition) marks the change from one type of response to the other. The concentrations of both magnesium and lithium affect the threshold level. An electron trap, represented by an optical absorption band peaking at 1200 nm and a broad ESR spectrum centered at gc=1.82, is observed in several of the heavily‐doped crystals after irradiation. A corresponding hole trap produced during the same irradiation has an optical absorption peak near...