We demonstrated that a new intermediate composition of Ba(1.55)Ca(0.45)SiO4 between the orthosilicates Ca2SiO4 and Ba2SiO4 yields the best phosphor hosts, and interesting luminescence properties can be found from the Eu(2+) singly doped and/or Eu(2+)/Mn(2+) codoped Ba(1.55)Ca(0.45)SiO4 phosphors. The phosphors can be excited by near-ultraviolet (nUV) light at wavelengths ranging from 200 to 450 nm matching well with the nUV light-emitting diode (LED) chips. As a result of fine-tuning the activators of different Eu(2+) content and Eu(2+)/Mn(2+) couples with different ratios, tunable full-color emission under UV light excitation can be realized by combining the blue emission (460 nm) and green emission (520 nm) originating from Eu(2+) with the red emission (595 nm) from Mn(2+) in the Ba(1.55)Ca(0.45)SiO4 host lattice. Energy-transfer efficiency between Eu(2+) and Mn(2+) increases and tunable emission can be obtained with increasing Mn(2+) doping content. These results indicate that the Ba(1.55)Ca(0.45)SiO4:Eu(2+),Mn(2+) phosphor will have potential use in nUV chip pumped white LED devices.