Optical activity of BSO crystals doped with Cr, Mn and Cu

The influence of both photochromic doping and photochromic transitions on the optical activity (OA) of undoped and doped Cr, Mn and Cu Bi12SiO20 (BSO) crystals is studied. The results show that Cr strongly increases the optical rotatory power ρ of BSO up to 70–80% below 520 nm and decreases it (with about 40–50%) at the long-wavelength region. Mn decreases ρ of BSO: with about 3–4% in the range 480–700 nm, whereas Cu increases it with about 7–8% in the same range. The relation between OA and absorption is discussed. The results lead us to the assumption that Cr3+ occupies Bi3+-tetrahedral (Td) positions, while Mn4+/5+ occupies Si-tetrahedral positions. The opposite influence of Cu2+ on ρ of BSO suggests that the Cu2+-ion preferentially replaces Si in BSO. In the co-doping cases, obviously, Al3+ predominately displaces Cr3+ from its Bi3+-Td M-sites. In the case of BSO:P, the results undoubtedly indicate that Cr3+ displaces P5+.