Study on synthesis and properties of Na+–La3+ co-doped γ-Ce2S3 pigment by low-temperature self-propagating combustion method

Na⁺–La³⁺ co-doped γ-Ce₂S₃ (abbreviated as γ-Na_0.5Ce_{2.5 − x}La_xS₄) pigments with a fixed Na/(Ce_1 − xLa_x) molar ratio of 0.2 (x = 0, 0.1, 0.5, 0.9, 1.3, 1.7, 2.1 and 2.5) were synthesized by low-temperature self-propagating combustion method. By adjusting the La³⁺ doping ratio, a series of γ-Na_0.5Ce_{2.5 − x}La_xS₄ pigments with different colors were obtained by sulfurizing at 900°C for 2 h using CS₂ as the sulfur source. The effects of La³⁺ doping amount on the synthesis of γ-Ce₂S₃, crystal structure, color performance, and temperature stability were systematically studied. The results show that the pigments exhibited a single cubic γ-Ce₂S₃ phase throughout the range of x increasing from 0 to 2.5. Compared with the co-precipitation method, the particle size of the pigment obtained by the low-temperature self-propagating combustion method decreased from 620 to 310 nm. Furthermore, as La³⁺ content increased, the band gap of the sample gradually increased from 2.06 to 2.90 eV, causing the color to change from red (L* = 39.42, a* = 40.35, b* = 30.28) to orange-red (L* = 49.15, a* = 35.51, b* = 40.64), then to orange-yellow (L* = 54.85, a* = 28.53, b* = 37.30), and finally to white-blue (L* = 66.66, a* = − 1.42, b* = 11.25). In addition, the thermal stability of γ-Na_0.5Ce_{2.5 − x}La_xS₄ was evaluated by TG-DSC and its thermal stability increased from 350 to 480°C.