Photochromic effect in LiNbO_3: Fe :Co

Abstract

In this paper, Co(2)O(3) was codoped in LiNbO(3): Fe crystals. It was found that Co codoping can give rise to the strong photochromic effect in LiNbO(3): 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 O(2-) to Fe(3+) directly while holes are thermally excited from O- into the valence band and then partly trapped by Co(2+), which leads to the darkening of the crystal. In bleaching process, the electrons are excited from Fe(2+) to the conduction band by green light and recombine with the holes on the Co(2+) level. Sensitizing/bleaching experiments were also carried out in LiNbO(3): Fe: Co crystals. Fast sensitization found for this material is beneficial to two-color recording.