Investigation of point defects in lithium niobate by electron spin resonance, electron nuclear double resonance, and optical absorption

Scope and method of study. The objective of this study is to investigate the point defects in a series of LiNbO{dollar}sb3{dollar} crystals which are either undoped, co-doped with magnesium and iron, or titanium doped. Electron spin resonance (ESR), electron nuclear double resonance (ENDOR), and optical absorption techniques were used to study the point defects produced in these materials by x-irradiation and high-temperature reducing treatments.; Findings and conclusions. Room-temperature irradiation of LiNbO{dollar}sb3{dollar} with x-rays converted Fe{dollar}sp{lcub}3+{rcub}{dollar} ions to Fe{dollar}sp{lcub}2+{rcub}{dollar} ions. Thermal annealing to approximately 120{dollar}spcirc{dollar}C reversed this process. Separate experiments in which LiNbO{dollar}sb3{dollar}:Fe,Mg were reduced at high temperature in an argon atmosphere revealed the conversion of Fe{dollar}sp{lcub}3+{rcub}{dollar} ions to Fe{dollar}sp{lcub}2+{rcub}{dollar} ions as well as the removal of the infrared absorption band due to OH{dollar}sp-{dollar} molecules and the production of absorption bands at 1300 nm and 460 nm. Two different environments for Fe{dollar}sp{lcub}3+{rcub}{dollar} ions in LiNbO{dollar}sb3{dollar}:Fe,Mg crystals are suggested by 35-GHz electron spin resonance results.; Reduction of LiNbO{dollar}sb3{dollar}:Ti samples in an argon atmosphere converts Ti{dollar}sp{lcub}4+{rcub}{dollar} ions to Ti{dollar}sp{lcub}3+{rcub}{dollar} ions. Optical absorption data from reduced samples reveal absorption bands at 660 nm and 450 nm. Samples subjected to ionizing radiation at 77 K also show the conversion of Ti{dollar}sp{lcub}4+{rcub}{dollar} ions to Ti{dollar}sp{lcub}3+{rcub}{dollar} ions. Optical absorption of 77-K x-irradiated samples reveals two overlapping absorption bands near 450 and 510 nm.; ENDOR experiments on Ti{dollar}sp{lcub}3+{rcub}{dollar} ions in a LiNbO{dollar}sb3{dollar}:Ti sample irradiated at 77 K suggests an environment different from that found for Ti{dollar}sp{lcub}3+{rcub}{dollar} ions in an argon-reduced LiNbO{dollar}sb3{dollar}:Ti sample.