Abstract
In this paper, Co2O3 was codoped in LiNbO3: Fe crystals. It was found that Co codoping can give rise to the strong photochromic effect in LiNbO3: Fe. Based on the UV-VIS-NIR absorption spectra, photorefractive sensitivities, and EPR results for both virgin and sensitized states of the crystal, the photochromic mechanism in this material was suggested as follows. During sensitization, electrons transfer from O2- to Fe3+ directly while holes are thermally excited from O- into the valence band and then partly trapped by Co2+, which leads to the darkening of the crystal. In bleaching process, the electrons are excited from Fe2+ to the conduction band by green light and recombine with the holes on the Co2+ level. Sensitizing/bleaching experiments were also carried out in LiNbO3: Fe: Co crystals. Fast sensitization found for this material is beneficial to two-color recording. (c) 2007 Optical Society of America.