The role of Gd3+ in enhancing Eu3+ luminescence intensity of Ca-4(Y, Gd)O(BO3)(3):Eu3+ under excitation by vacuum UV light was investigated. A dominant excitation band peaked at 175 nm is assigned to the transitions from O 2p valence state to mixed states of B 2p and Y 4d orbitals on the basis of calculation by the relativistic DV-X alpha method, which is a popular computational code of the molecular orbital calculation. The 175 nm band is related also to Gd3+, because its intensity increases with Gd molar fraction. Presumably excitation energy absorbed by the above transitions is transferred to Eu3+ via the 4f excited levels of Gd3+, because both the charge transfer and 4f-5d transition energy of Gd3+ are much higher than the photon energy of the 175 nm band. (C) 2008 The Electrochemical Society.