X-ray induced reduction of rare earth ion doped in Na₂O-Al₂O₃-B₂O₃ glasses

5Na₂O-10Al₂O₃-85B₂O₃ glasses doped with 0.05 mol% Sm₂O₃ or 0.05 mol% Eu₂O₃ turn to orange after irradiation by focussed femtosecond pulsed laser or x-ray irradiation. To know the mechanism of photo-induced coloring, the glasses were studied by Sm or Eu L_III XANES before and after x-ray or UV irradiation. XANES in both edges showed that a part of trivalent ion converted to divalent ion upon the irradiation of x-ray. These facts reveal that photoreduction of rare earth ion is the mechanism of photo-induced coloring. However no photoreduction upon UV irradiation occurred in both glasses.