Although SiO 2 crystals have been used in electroluminescence devices and thermoluminescence (TL) dosimeters, the emission mechanism of TL has not yet been clearly explained. Recently, as we could get amorphous and highly pure SiO 2 prepared by the sol-gel method, we have investigated the TL emission mechanism using Al 3 + - and/or Eu 3 + -doped SiO 2 crystalline samples prepared by the heat-treatment under much lower temperature that the melting point of SiO 2 . The TL spectrum of the Eu 3 + -doped sample displayed several peaks, including two main peaks due to the electron transitions from 5 D 2 to 7 F 5 (ca. 570nm) and from 5 D 0 to 7 F 2 (ca. 610nm). As doping concentration increased, all the peak intensities reduced from maximum values except that due to the electron transition from 5 D 0 to 7 F 2 . These observations are thought to result from a cross-relaxation process due to the lack of inversion symmetry at the Eu 3 + site.