Eu²⁺-activated reddish-orange-emitting Ca₃Si₂O₇ phosphors were synthesized with the addition of NH₄Cl flux. When the phosphors were synthesized in a nominal composition of (Ca_0.99Eu_0.01)₃Si₂O₇ without flux addition, a Ca₃Si₂O₇ phase responsible for reddish-orange emission was identified to coexist with an intermediate phase of a-Ca₂SiO₄ for green emission. With the addition of NH₄Cl flux, a-Ca₂SiO₄ was suppressed while the pure phase Ca₃Si₂O₇ was obtained as the flux content was 3 wt%. Through varying the amount of flux, the emission color of samples can be tuned from green to reddish-orange, corresponding to the phase transformation from a-Ca₂SiO₄ to Ca₃Si₂O₇. Through optimizing the doping concentration of Eu²⁺, the optimized photoluminescence (PL) properties for reddish-orange emission can be achieved, which makes this kind of phosphor prospective in the applications of the phosphor-converted white light emitting diodes (PC-WLEDs).