Synthesis and optical properties of Eu³⁺ ion-doped La₂O₂S₂ via a solid state reaction method using La₂O₂SO₄ as a raw material

La₂O₂S₂:Eu³⁺ was successfully synthesized by using La₂O₂SO₄, Na₂CO₃ and sulphur as raw materials through a solid-state reaction (SSR) method. XRD results indicate that all of the diffraction peaks of the obtained sample are consistent with the standard pure phase of La₂O₂S₂ with an optimal molar ratio (La₂O₂SO₄:S:Na₂CO₃ = 1:30:5) and reaction temperature (500 °C). An infrared carbon and sulphur analysis instrument shows that the average value of the sulphur concentration in the target product is approximately 16.5039%, which is close to the theoretical data (17.1123%). The above-mentioned results illustrate the feasibility of the reaction process. SEM images show that the morphology of the product changed from a near-spherical (the precursor and La₂O₂SO₄) to near-quadrilateral structure (La₂O₂S₂) over the entire reaction process, with sizes varying from ~ 10 nm to ~ 200 nm. The optical band gap of La₂O₂S₂ is approximately 2.55 eV, which is desired for photocatalytic applications. After being excited by a 325-nm laser at 77 K, La₂O₂S₂:Eu³⁺ exhibited good photoluminescence properties, and a strong red emission at approximately 612 nm can be observed due to the ⁵D₀→⁷F₂ transition of Eu³⁺ ions.