Photochromic effect in Fe- and Mn-doped Bi4Ge3O12 crystals

Bismuth germanate (Bi4Ge3O12) single crystals are used in detection systems for high energy photons and particles, because of their room temperature scintillator capability. Recently light-induced holographic gratings have been formed in transition metal doped Bi4Ge3O12. In both applications the impurities play an important role in the optical behaviour of the material: a) Residual impurities in Bi4Ge3O12 crystals are responsible for the decrease of the luminescence yield. b) Transition metal ions induce photorefractive and photochromic behaviour that contribute to the diffraction efficiency of the gratings. The aim of our paper is to present a detailed study of the photochromic phenomenon in iron and manganese doped Bi4Ge3O12 crystals. The intention is to clarify the role of these impurities in the colouration processes. The optical absorption and electron spin resonance spectra of the Fe3+ and Mn2+ ions have been monitored. (author)