In the search for well-defined phosphor materials for white NUV-LEDs, the highly enhanced luminous efficacy by N^3– doping as well as color tunability via Ca substitution has been successfully obtained in Ba_2–xCa_xSiO_4−δN_2/3δ:Eu²⁺ (x = 0.0, 0.5, 0.8, 1.0) phosphors. With increasing Ca-substitution rate, the crystal structures of the phosphor materials are changed from the primitive orthorhombic structure to the hexagonal one, so that the CIE coordinates move from bluish-green (at Ca = 0.0), to blue (at Ca = 0.5), and finally to near white region (at Ca = 0.8 and 1.0) in these materials. In combination with the results from X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy, the elemental distribution of the phosphor materials found from secondary-ion mass spectrometry (SIMS) directly indicates that the N^3– ions are partially substituted for O^2– ions into the crystal lattice of alkaline-earth orthosilicates and thus critically improves the color-tunable photoluminescence (PL) and electroluminescence (EL) efficiency of the phosphor materials for white NUV-LEDs. The newly found “the N^3– doping and color-tunable effect” on large PL and EL enhancement may provide a platform in the discovery of new efficient phosphors for solid state lighting.