The geometrical structure and electronic properties of trivalent Ho doped YO crystals: a first-principles study.

Trivalent rare-earth holmium ion (Ho) doped yttrium oxide (YO) has attracted great research interest owing to its unique optoelectronic properties and excellent performances in many new-type laser devices. But the crystal structures of the Ho-doped YO system (YO : Ho) are still unclear. Here, we have carried out a first-principle study on the structural evolution of the trivalent Ho doped YO by using the CALYPSO structure search method. The results indicate that the lowest-energy structure of Ho-doped YO possesses a standardized monoclinic 2 phase. It is found that the doped Ho ion are likely to occupy the sites of Y in the host crystal lattice, forming the [HoO] local structure with site symmetry. Electronic structure calculations reveal that the band gap value of Ho-doped YO is approximately 4.27 eV, suggesting the insulating character of YO : Ho system. These findings could provide fundamental insights to understand the atomic interactions in crystals as well as the information of electronic properties for other rare-earth-doped materials.