We synthesized a violet-blue phosphor Ba 2 AlB 4 O 9 Cl:Eu 2+ with a solid-state reaction. The excitation and emission spectra of this phosphor showed that all were broadband due to 4f 7 - 4f 6 d 1 transitions of Eu 2+ . The phosphors with different Eu 2+ concentrations presented violet-blue luminescence for ultraviolet [(UV) 250-390 nm] excitation. The optimum concentration of Eu 2+ in Ba 2 AlB 4 O 9 Cl:Eu 2+ is determined to be 6 mol:%. The luminous efficiency was found to be 8:1 lm/Wfor the violet-blue fluorescent lamp and 3:2 lm/W for the violet-blue phosphor-converted light-emitting diode, respectively. Ba 2 AlB 4 O 9 Cl:Eu 2+ would be a promising phosphor for converting the UV radiation to violet-blue emission for a novel high light-conversion efficiency phototherapy illuminator.