Excitation with band edge light at low temperatures produces an emissi
on near 2.9 eV in both hydrothermally and Czochralski grown Bi12SiO20
samples. The emission band is much stronger in the hydrothermal sample
s. It disappears when the samples are heated to 50 K. A weak 1.9 eV em
ission is also observed in the Czochralski samples. This emission grow
s when the 2.9 eV decays near 50 K and then goes out between 100 and 1
50 K.