The irradiation of Eu (3+) -ion-doped glass s by X-rays allows a new holeformation phenomenon, being neither persistent nor transient, to be observed. The stable, persistent formation of spectral holes occurs by two-step electron transfer through an activated Eu (3+) -ion state during laser irradiation (see figure). This new observation is very significant when considering the hole-burning mechanism and developing new persistent spectral hole-burning (PSHB) materials.