Intense optical absorption of defects created in Er ³⁺-diffused layer in MgO (5 mol%)-doped LiNbO ³ crystal by local Er ³⁺ diffusion under Li-poor atmosphere

Intense broad absorption bands centered around 1.7, 2.5, 3.1, and 3.7 eV take place in Er ³⁺-diffused layer formed near MgO (5 mol%)-doped LiNbO3 crystal surface by in-diffusion of Er metal under Li-poor atmosphere. These bands are tentatively attributed to the defect absorption of small polarons, bipolarons, F-centers, and Q-polarons created due to Er ³⁺ in-diffusion and Li2O loss from the crystal. It is interesting that the number, type, area, and peaking position of the bands can be controlled by the diffusion temperature and further oxidation treatment. Such material is a promising medium for data storage based upon two-color holography.