Photoluminescence excitation spectra of lanthanide doped YAlO 3 in vacuum ultraviolet region

Abstract To understand luminescent mechanisms of lanthanide (Ln) doped phosphors, it is important to know the energy positions of unoccupied Ln 2+ 4 f and Ln 3+ 5 d states, as well as occupied Ln 3+ 4 f states, relative to the energy bands of host materials. Photoluminescence excitation (PLE) spectra of Ln doped YAlO 3 were measured in a vacuum ultraviolet (VUV) region and the energy positions of Ln 2+ 4 f and Ln 3+ 5 d states in the wide-gap YAlO 3 were elucidated. Peaks assignable to host lattice excitation were observed in all samples at approximately 8 eV in the PLE spectra. PLE peaks derived from charge transfer (CT) and 4 f -5 d transitions were observed at lower energy than the bandgap energy. Ln 2+ 4 f energy levels were obtained from the PLE peak energies for the CT transitions along with the valence band maximum. In contrast, Ln 3+ 5 d energy levels were evaluated from those for the 4 f -5 d transitions along with the Ln 3+ 4 f energy levels, which were obtained previously from X-ray photoelectron spectroscopy measurements. The elucidated Ln 2+ 4 f and Ln 3+ 5 d energy levels were exhibited in an energy diagram together with Ln 3+ 4 f energy levels and host energy bands. The experimental Ln 2+ 4 f and Ln 3+ 5 d energy levels were in good agreement with the reported theoretical data.