Introduction Bi4Ge3O12 (BGO) single crystals are widely used as high-energy X- and c-ray scintillation detectors, originally proposed by Weber and Monchamp [1]. A review paper describing the crystal growth, structure, optical, luminescence and scintillation characteristics including the doped crystals was published in late 1980s [2]. There has been quite some discussion about the nature of the absorption and emission processes in this material: It has been firstly ascribed to the transition between the ground (1 S0) and excited (3 P1) states of Bi3+ ion [1], later on described rather as a self-trapped exciton state based on Bi(GeO4)6 cluster [3]. Recent electronic band structure calculation points to the dominance of the absorption process from the oxygen 2p states (top of valence band) to Bi3+ 6p states (bottom of conduction band) [4], while the nature of the emission process is clearly based on the Bi3+ transition from 6p to 6s states mentioned above though the excitonic nature of the emission centers has been stressed as well [5].