CaSi2O2N2: Eu2+ phosphors with zinc acetate additive as a flux agent have been synthesized successfully by solid-state process. The structure, morphology, and photoluminescence (PL) properties of the compounds are investigated as a function of zinc acetate dihydrate (Zn(CH3COO)2·2H2O) dosage. X-ray diffraction (XRD) measurement indicates that the pure CaSi2O2N2 phase is obtained by adding appropriate amount of zinc acetate dehydrate. The sheetlike morphology of sample transforms into block as Zn(CH3COO)2·2H2O content reaching 43 wt%, associated with the increase in emission intensity. A strong absorption band from near ultraviolet (NUV) to visible range and a broad yellow emission band in the wavelength range of 460–700 nm are observed in Eu2+-doped CaSi2O2N2. High bright yellowish light emitting diodes are obtained by combining CaSi2O2N2:Eu2+ as the wavelength conversion phosphor with NUV InGaN LED-chip (395 nm). The bright yellowish emission and the low thermal quenching effect of CaSi2O2N2: Eu2+ with zinc acetate additive make it a potential phosphor converter for white LEDs.