Inorganic photochromic material is an available medium to obtain optical information storage. The photochromic property of the inorganic material is mainly from the defects of the host. However, the formation of defects in the host is uncontrollable, in particular, the revisable formation and removement of defects are difficult. Thus, there are few inorganic materials with the revisable photochromism upon the entire light stimulation. Therefore, it is an urgent need to find a suitable approach to design inorganic photochromic materials. Here, the photochromic PbWO 4 :Yb 3+ , Er 3+ ceramic was designed with the help of valence state change of W 6+ → W 5+ and Pb 2+ → Pb 4+ . Upon the 532 nm laser stimulation, the photochromism of the PbWO 4 :Yb 3+ , Er 3+ ceramic was obtained based on the Pb 2+ + hν (532 nm) → Pb 4+ + 2e − and W 6+ + e − + hν (532 nm) → W 5+ reaction, resulting in the optical information writing. Under the stimulation of an 808 nm laser, the written optical information was erased based on the W 5+ + hν (808 nm) → W 6+ + e − and Pb 4+ + 2e − + hν (808 nm) → Pb 2+ reaction. In addition, the photochromism-induced upconversion emission modification was obtained in the PbWO 4 :Yb 3+ , Er 3+ ceramic, realizing the effective and nondestructive reading out of optical information. The cyclic experiment demonstrated a good reproducibility of both photochromism and upconversion emission modification, exhibiting the potential application of the PbWO 4 :Yb 3+ , Er 3+ ceramic as the optical data storage medium.

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S U M M A R YPassive seismic interferometry is a new promising methodology for seismic exploration. Interferometry allows information about the subsurface structure to be extracted from ambient seismic noise. In this study, we apply the cross-correlation technique to approximately 25 hr of recordings of ambient seismic noise at the Ketzin experimental CO 2 storage site, Germany. Common source gathers were generated from the ambient noise for all available receivers along two seismic lines by cross-correlation of noise records. This methodology isolates the interstation Green's functions that can be directly compared to active source gathers. We show that the retrieved response includes surface waves, refracted waves and reflected waves. We use the dispersive behaviour of the retrieved surface waves to infer geological properties in the shallow subsurface and perform passive seismic imaging of the subsurface structure by processing the retrieved reflected waves.