The persistent spectral hole-burning phenomenon was investigated for Sm2+ ions-doped Al2O3-SiO2 glasses prepared by the sol-gel method. The efficiency of hole-burning, burned at low temperature ~77K, was proportionally increased with the content of OH groups surrounding the rare-earth ions. The proposed mechanism for hole-burning was the optically activated rearrangement of the OH bonds surrounding the rare-earth ions. The burned-hole was thermally refilled and erased above ~200 K. On the other hand, the glasses obtained by heating in H2 gas or irradiating with x-rays showed PSHB up to room temperature. When heated in H2 gas, the H2 molecules react with oxygen ions to form H2O. Removal of the generated H2O causes the number of oxygen ions surrounding rare-earth ions to decrease, resulting into the reduction of the ions. The hole burning in the H2-treated glasses was performed by the electron transfer between the rare-earth ions and the trapping centers. In contrast, in the x-ray irradiated glass, it was concluded that the rear-earth ions are deuced into the divalent state by electron transfer from the oxygen defect center. The hole defect centers are trapped in oxygen ions bound with Al3+ ions. The spectral hole burning of the x-ray irradiated glasses could be burned by the reverse reaction of the reduction of the rare-earth ions. A short distance between the Sm2+ and oxygen defect centers brought a high-speed hole burning, that is, 30 times faster than in a similar H2 gas treated glass.