Novel single-phased white light-emitting KCaY(PO4)(2):Eu2+,Mn2+ phosphors for light-emitting diode (LED) applications were synthesized by conventional solid-state reaction. The emission hue could be controlled by tuning the Eu2+/Mn2+ ratio via the energy transfer; the the emission hue of KCaY(PO4)(2):Eu2+,Mn2+ varied from blue (0.1853, 0.2627) to white-light (0.3350, 0.3203) and eventually to purple (0.3919, 0.2867). The mechanism of energy transfer from a sensitizer Eu2+ to an activator Mn2+ in KCaY(PO4)(2):Eu2+,Mn2+ phosphors was demonstrated to be an electric dipole-quadrupole interaction. Combining a NUV 405-nm chip and a white-emitting KCaY(PO4)(2):1%Eu2+,4%Mn2+ phosphor produced a white-light NUV LED, demonstrating CIE chromaticity coordinates of (0.314, 0.329) and a color temperature of 6507 K.