The influence of both photochromic doping and photochromic transitions on t
he effect of magnetooptical rotation (Farady effect - FE) of undoped and do
ped with Cr, Mn and Cu Bi12SiO20 (BSO) and Bi12TiO20 (BTO) crystals is stud
ied. The present results show, that Cr, Mn and Cu increase the FE. The infl
uence of Cr, whose affect on the optical activity (OA) of BSO is most signi
ficant, here is too negligible (Verdet coefficient (V) increases only with
1-2 % in the range 700 - 590 nm). The Mn-doping of BSO led to a V-increase
with about of 11 % in the range 400 - 700 nm, as at 460 nm the relative inc
rease of V reaches to about 30 %. The influence of Cu on FE in BSO (likely
the case of the natural optical rotation) is again significant. Thus, the i
nfluence of V in the case of BSO:Cu is about 18 % in the range 700 - 480 nm
as reaches 28 % in the shortwave region at 480 nm. However, in BTO:Cu (0.0
2 mol.% Cu) the influence of Cu is opposite in respect of both effects. Now
the values of V increase with 21 % at 630 nm, 22 % at 590 nm, 42 % at 520
nm, and 73 % at 480 nm in comparison to BTO-undoped.