Abstract
The spectra of absorption, luminescence and excitation in a pure BGO (Bi 4 Ge 3 O 12 ) crystal have been observed at several temperatures (10-300 K). The steepness constant of the Urbach tail in the exciton absorption is obtained to be 0.56, from which we conclude that the self-trapped exciton is stable in BGO. Based on the results we assign the luminescence of BGO to the self-trapped exciton.