The role of divalent ions in persistent hole-burning mechanism in Y2O3:Pr3+ crystals

Persistent spectral hole-burning is extensively studied in many materials. In inorganic materials doped with rare earth ions, we have mainly two mechanisms for hole-burning; one is optical pumping to hyperfine sublevels in rare earth ions, and the other is optically induced rearrangement of local structure around optical centers. In crystals we often observe the hole due to the former mechanism while the hole due to the latter is reported mainly in glasses. Up to now, there seems to be only little study about the correlation between the mechanism of hole-burning and sample-quality or defects. Recently we reported that the character of holes in Y2O3:Pr3+ depends on the quality of samples [1]. In this paper we study the origin of these holes in Y2O3 with a well-controlled manner. For this purpose, we applied hole-burning spectroscopy to various Y2O3:Pr3+(0.2mol%) samples doped with other metallic ions.