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

Na+-La3+ co-doped gamma-Ce2S3 (abbreviated as gamma-Na0.5Ce2.5 - xLaxS4) pigments with a fixed Na/(Ce1 - xLax) 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 gamma-Na0.5Ce2.5 - xLaxS4 pigments with different colors were obtained by sulfurizing at 900 degrees C for 2 h using CS2 as the sulfur source. The effects of La3+ doping amount on the synthesis of gamma-Ce2S3, crystal structure, color performance, and temperature stability were systematically studied. The results show that the pigments exhibited a single cubic gamma-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 gamma-Na0.5Ce2.5 - xLaxS4 was evaluated by TG-DSC and its thermal stability increased from 350 to 480 degrees C.