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

Abstract 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.