Reversible Mn valence state switching in submicron α-Al 2 O 3 :Mn by soft X-rays and blue light - a potential pathway towards multilevel optical data storage.

The generation of Mn 4+ in α-Al 2 O 3 :Mn 3+ by soft X-ray exposure is demonstrated with a large dynamic range of the X-ray generated Mn 4+ luminescence signal, indicating the potential use of α-Al 2 O 3 :Mn 3+ for multilevel optical data storage. Samples with a range of Mn concentrations (0.05, 0.1, 0.2, 0.4, 0.6 and 1.2 atom%) were prepared via a facile combustion method and the sample with 0.4 atom% was found to display the highest luminescence intensity. The stored information can be read out via the R -lines ( 2 E → 4 A 2 ) under ∼470 nm ( 4 A 2 → 4 T 2 ), or ∼630 nm ( 4 A 2 → 2 T 1 ) excitation with the latter being preferred since photobleaching is minimized. Interestingly, the Mn 4+ valence state can be fully switched back to Mn 3+ by blue light exposure ( e.g. , 462 nm laser diode). The stored information could be repeatedly written and erased, showing no significant deterioration over five consecutive cycles, with less than 5% uncertainty.