Sm2+ ion-doped Al2O3–SiO2 glasses were prepared using sol-gel and melt-quenching methods; the redox equilibrium and spectral hole burning were investigated. The Sm3+ ions were reduced into Sm2+ by heating in H2 gas or x-ray irradiation. The redox between the Sm3+ and Sm2+ obeyed first-order kinetics, the rate of which was larger for the sol-gel glasses. The Sm3+ ions were also reduced by x-ray irradiation and the activation energy for redox equilibrium was half of that for the glasses treated in H2 gas. Two different mechanisms were proposed for the redox reaction of the samarium ions. In the x-ray irradiated glasses, the Sm3+ ions were reduced into Sm2+ by electron transfer from the oxygen defect center, whereas the H2-gas reaction removed the oxygen ions to reduce the Sm3+ ions. The spectral hole burning of the x-ray-irradiated glasses could be burned by the reverse reaction of the reduction of the Sm3+ ions; that is, the electron transfer from the excited Sm2+ into the surrounding oxygen. A short distance between the Sm2+ and oxygen defect centers allowed fast hole burning. On the other hand, the hole burning in the H2-treated glasses was performed by electron transfer between Sm2+ and another trapping center such as Sm3+.
Room temperature persistent spectral hole burning in x-ray irradiated Eu3+-doped borate glasses