Low-temperature vaterite-type LuBO3 (pi-LBO) was prepared by a solid-state reaction method at high temperature. The reasoning of the existence of vacancy-stabilized pi-LBO was investigated for the first time using neutron diffraction patterns, Fourier transform infrared (FT-IR) spectra, and high-resolution transmission electron microscopy. The results clearly demonstrated that the B and O vacancies in pi-LBO came into being during the heating process. The existence of an open B3O9 ring consisting of BO3 and BO4 units in pi-LBO due to the B and O vacancies was demonstrated by FT-IR. The vacuum ultraviolet-ultraviolet spectroscopic properties of pi-LBO were studied in detail. In addition, the luminescence mechanism of Ce3+ in pi-LBO was put forward and discussed with that of calcite-type LuBO3 (beta-LBO).