Luminescence study of NaMgF3:Ho and NaMgF3:Er: X-ray induced reduction Ho3+→ Ho2+

X-ray induced reduction Ho3+ -> Ho2+ was observed in polycrystalline samples of NaMgF3:Ho. Prior to irradi-ation, only luminescence arising from 4f10 <-> 4f10 transitions of Ho3+ was observed. After irradiation, excitation bands arising from 4f11 -> 4f10(5IJ)5d1 transitions of Ho2+ were observed in the visible spectral region, and a corresponding 4f11(4I13/2) -> 4f11(4I15/2) emission was observed that peaked in the infrared at 1808 nm. The emissions of Ho3+ were compared with those of Dy2+, and the emissions of Ho2+ were compared with those of Er3+, in order to calculate the isoelectronic compression factors xi(4f10) = 1.17 and xi(4f11) = 1.18 for the isoelectronic Ln3+/Ln2+ pairs in the NaMgF3 host. The Ho reduction was reversible, where continuous stimu-lation with 360 nm light released trapped electrons such that Ho2+ -> Ho3+. This optically reversible Ho2+ <-> Ho3+ conversion may find applications in radiation sensing and optical data storage.