Electron paramagnetic resonance investigation of the photochromic effect in near-stoichiometric LiNbO3 with applications to holographic storage

Near-stoichiometric LiNbO3 (LiNbO3, LiNbO3:Tb, and LiNbO3:Tb,Fe) crystals h ave exhibited a reversible photochromic effect at room temperature. Irradia tion by UV light induced a visible absorption band extending from lambda ap proximate to 650 nm to the absorption edge, which could be bleached by subs equent illumination with visible light. Electron paramagnetic resonance (EP R) analysis at 15 K revealed an EPR signal of g approximate to2.0 appearing after UV irradiation with a simultaneous decrease in the Fe3+ signal inten sity. This implies that the Fe3+ ions (natural impurities or dopants) act a s electron traps and the induced absorption band is caused by the charge tr ansfer from UV-sensitive absorption centers to Fe3+ ions via the conduction band. Using the induced absorption band, a high-sensitive holographic reco rding has been achieved with a continuous-wave green laser at lambda approx imate to 532 nm. In addition, the fast response to UV light made it possibl e to quickly erase the stored information by UV illumination. (C) 2001 Amer ican Institute of Physics.