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.