In this study, the influences of different aid-sintering additives on the synthesis of β-SiAlON:Eu²⁺ phosphor were investigated. The aid-sintering additives include oxides, fluorides, chlorides, and carbonates. The β-SiAlON:Eu²⁺ phosphor, synthesized using different additives, was investigated in detail via spectroscopic data, X-ray diffraction, quantum efficiency, and scanning electron microscopy; the particle morphology and spectroscopic properties improved with the addition of different additives. Different additives have different influences on the morphology of β-SiAlON:Eu²⁺. Most oxide additives increase the diameter of β-SiAlON:Eu²⁺. Most fluoride additives increase the length of β-SiAlON:Eu²⁺. Particles with different morphologies can be obtained by adjusting the quantities of the oxide and fluoride additives. When combined with red phosphors, β-SiAlON:Eu²⁺ will produce wider color gamut backlights than the traditional yttrium aluminum garnet.