Yellow emitting Sm ₃₊-doped NaBa _1-x BO ₃(0.01 ≤ x ≤ 0.13) phosphors were synthesized by conventional solid state reaction method. The phase structure and luminescence properties of the as-prepared phosphors were investigated. These phosphors can be effectively excited by 403 nm near-ultraviolet light and feature a satisfactory yellow performance. The emission peaks are observed at 560 nm, 603 nm and 650 nm, originating from the transitions of ⁴G_5∕2→⁶H_5∕2, ⁴G_5∕2→⁶H_7∕2 and ⁴G_5∕2→⁶H_9∕2 respectively. Investigation of Sm ³⁺ concentration-dependent emission spectra indicates that the NaBa _0.95 BO ₃:0.05 Sm ³⁺ phosphor shows the strongest yellow emission intensity and exhibits the CIE value of x = 0.4760 and y = 0.5090. Through the theoretical calculation, a high color purity of 96.0% was determined for the NaBaBO ₃: Sm ³⁺ phosphor, and the color purity of NaBaBO ₃: Sm ³⁺ is much higher than that of the commercial yellow phosphor YAG : Ce ³⁺. This work is highly relevant to the development of a new type of potential down-conversion (DC) yellow phosphor for near ultraviolet white or yellow light-emitting diodes (LEDs).