PHOTOCHROMIC BEHAVIOR OF DOPED BI4GE3O12 SINGLE-CRYSTAL SCINTILLATORS

The changes induced by ultraviolet (UV) illumination on the optical absorption and electron paramagnetic resonance (EPR) spectra of Bi4Ge3O12 single crystals, doped either with Fe (and Gd) or Mn, have been followed at room temperature (RT). In both crystals several overlapping optical absorption bands develop under UV illumination, covering from almost-equal-to 0.7 eV up to the band edge of the matrix. The optical damage can be bleached by heating the samples above RT or by illumination with visible light. Although these optical changes temporarily correlate with the variation of the Gd3+ and Mn2+ concentrations, it has been concluded that other defects are present and partially responsible for the optical damage.