<p>A systematic investigation was carried out on samarium (Sm³⁺)-doped NaBaPO₄ orange-yellow-emitting phosphors synthesized via a solid-state process in an air atmosphere, focusing on determining how the crystallization behavior and luminescence mechanisms are affected by the calcination time and dopant concentration. The phase formation and optical properties were characterized using thermogravimetry, X-ray powder diffraction, and photoluminescence spectroscopy. The results demonstrate that the sample calcined at 750° forms the main phase of hexagonal NaBaPO₄ (space group <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(P\overline{3 }ml\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>P</mi> <mover> <mn>3</mn> <mo>¯</mo> </mover> <mi>m</mi> <mi>l</mi> </mrow> </math></EquationSource> </InlineEquation>), which contains two distinct crystallographic sites for Ba²⁺ ions. Excitation at 400 nm reveals strong near-UV absorption, indicating suitability for matching LED devices. The emission spectra exhibit transitions at 564 nm (⁴<i>G</i>_5/2 → ⁶<i>H</i>_5/2, magnetic dipole), 600 nm (⁴<i>G</i>_5/2 → ⁶<i>H</i>_7/2, mixed character), and 644 nm (⁴<i>G</i>_5/2 → ⁶<i>H</i>_9/2, electric dipole). The hypersensitivity of the ⁴<i>G</i>_5/2 → ⁶<i>H</i>_9/2 transition to the local crystal field enables precise emission tuning via symmetry engineering. Variations in the red-to-green intensity ratio of the emission peaks with Sm³⁺ content allow modulation of the chromaticity coordinates and color purity. Among the investigated samples, the maximum emission intensity is achieved by NaBa_0.97PO₄:0.03Sm³⁺, for which the quenching mechanism is identified as multipole–multipole interactions. Additionally, the highest color purity (96.3%) is also achieved by this phosphor, exhibiting a highly saturated color.</p>