For light-emitting diode (LED) excitation at 400 nm, the optical properties of a Eu 2þ -activated CaO-SrO-MgO-SiO 2 material system were investigated. All the materials were synthesized by solid state reaction. In particular, (Ca,Sr)Mg 2 Si 3 O 9 :Eu 2þ , which has the same crystal structure as CaMgSi 2 O 6 , was found to be promising as a blue-light-emitting phosphor for near UV LED application. The luminance intensity was optimized by controlling the Eu 2þ concentration and the composition of the host lattice. The ratio of calcium ions to strontium ions was a convenient parameter for adjusting the maximum excitation peak to 400 nm, which is favorable for near UV LED excitation. The highest luminance intensity of Ca 1ÀxÀy Sr y Mg 2 Si 3 O 9 :Eu x 2þ under 405 nm excitation was achieved at the Eu 2þ concentration of x ¼ 0:01 and a Sr 2þ concentration of y ¼ 0:3. The luminance intensity of (Ca,Sr)Mg 2 Si 3 O 9 :Eu 2þ was found to be superior to that of a commercial blue-light-emitting BaMgAl 10 O 17 :Eu 2þ phosphor, which is used for near-UV LED excitation. #