Optical Transitions near the Fundamental Absorption Edge and Electronic Structures of YAl₃(BO₃)₄:Gd³⁺

Abstract

Optical properties of Gd3+ ions doped in YAl3(BO3)4 are investigated as a new UV phosphor under excitation of VUV radiation. A strong emission line at 3.96 eV (313 nm) corresponding to the transitions from the 6P7/2 to 8S7/2 states of Gd3+ ions is observed. We performed the Rietveld refinement using an X-ray diffraction result to obtain the structural parameters of a synthesized YAl3(BO3)4:Gd3+ phosphor. From the result, it is shown that the refined crystal structure of YAl3(BO3)4:Gd3+ phosphors is slightly distorted. The electronic structures have been calculated using the relativistic discrete variational Xα method. The calculations indicate that the optical properties of a non-doped YAl3(BO3)4 crystal near the fundamental absorption edge are characterized by the electronic transitions from O 2 p valence states to B 2 p conduction states. On the other hand, it is found that the origin of the absorption edge of YAl3(BO3)4:Gd3+ phosphor is due to the transitions from O 2 p states to mixed states of mainly B 2 p and Y 4d orbitals.