Formation of Sm2+ Ions and Spectral Hole Burning in X-ray Irradiated Glasses

Al 2 O 3 −SiO 2 glasses were prepared for doping with Sm 3+ ions using a sol−gel method, followed by X-ray irradiation, in which formation of the Sm 2+ ions and persistent spectral hole burning (PSHB) were investigated. The X-ray irradiation brought about hole centers in the oxygen ions bound with Al 3+ ions. And the released electrons are captured in the Sm 3+ ions to form Sm 2+ ions. The X-ray reduced Sm 2+ ions are not so stable that they change into Sm 3+ by heating at 200 to 300 °C. The spectral holes were burned in the 7 F 0 → 5 D 0 line of the Sm 2+ ions, in which deep holes could be burned within a short laser-irradiation period compared with that of the H 2 -gas heated glass. Hole spectra were stable up to room temperature, at which the hole depth was ∼20% of the total fluorescence intensity. Bleaching at the low energy sites of the 7 F 0 → 5 D 0 transition was observed during irradiation with the laser. The results definitely reveal that the PSHB is formed by the electron transfer between the Sm 2+ ions and the hole centers formed in oxygen ions bound through the excited 5 D 0 state.