[en] Highlights: • La₂O₂S:Tb^{3 +} phosphors can be successfully synthesized by a one-step K₂CO₃/Na₂CO₃ flux method. • As-prepared La₂O₂S:Tb^{3 +} phosphors have good thermal stability, lifetime and quantum efficiency. • La₂O₂S:Tb^{3 +} embedded PMMA films can also achieve near ideal green light (x = 0.21, y = 0.71). • La₂O₂S:Tb^{3 +} phosphors can be promising candidates for green-emitting materials. La₂O₂S:Tb^{3 +} phosphors were synthesized by a one-step K₂CO₃/Na₂CO₃ flux method and phosphor-embedded polymethylmethacrylate (PMMA) films were fabricated by spin coating. Effects of calcination temperature and flux on the crystal structure, morphology and luminescence performance were evaluated by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence and calculation of CIE color coordinates. In the emission spectra, several emission peaks corresponding to ⁵D₄ → ⁷F₆, ⁵D₄ → ⁷F₅, ⁵D₄ → ⁷F₄, and ⁵D₄ → ⁷F₃ transitions appeared, with the ⁵D₄ → ⁷F₃ green emission being the dominant emission. The energy band gap, quantum efficiency, fluorescence decay curves, and thermal stability were also investigated with the aim of exploring the potential applicability of the synthesized phosphors in optical devices.