Luminescence properties of Ca4GdO(BO3)3:Eu in ultraviolet and vacuum ultraviolet regions

The luminescent properties of Ca₄GdO(BO₃)₃:Eu³⁺ were investigated under excitation of UV and VUV light. Separate two broad bands at around 259 and 184 nm were observed in the excitation spectrum of Ca₄GdO(BO₃)₃:Eu³⁺. These peaks were assigned to the charge transfer transition of Eu³⁺-O²⁻ and Gd³⁺-O²⁻, respectively. Owing to the favorable spectral position in their broad intense excitation band, Eu³⁺ ions show a intense emission under 258 nm excitation in Ca₄GdO(BO₃)₃:Eu³⁺. This spectral position was determined by the free oxygen ions O (1). Ca₄GdO(BO₃)₃ doped with Eu³⁺ ion seems to be a preferable candidate as red lamp phosphor. On the other hand, a weak band with a maximum at about 184 nm was observed below 200 nm in the excitation spectrum of Ca₄GdO(BO₃)₃:Eu³⁺. This phosphor do not emit effectively under the 147 nm excitation. This unfavorable profile was also due to the O (1) ions, which played a role to the shifting towards the lower energy sides. The luminescence of Eu³⁺ ions in Ca₄GdO(BO₃)₃ was somewhat different from that observed in the other borates phosphors, but resembled to those observed in the oxide phosphors (e.g. Gd₂O₃, Y₂O₃ and Gd₂SiO₅). Such behavior was recognized by the detailed analysis of crystallographical surroundings around activator.