Sol-gel synthesis, crystal structure, surface morphology, and optical properties of Eu₂O₃-doped La₂Mo₃O₁₂ ceramic

In this paper, we report the synthesis of the La-Mo-O tartrate gel precursors with the initial composition for La₂Mo₃O₁₂ ceramic prepared from different starting materials by an aqueous sol-gel synthesis route using tartaric acid as a complexing agent. Moreover, the La-Mo-O carbonate-tartrate and nitrate-tartrate gel precursors doped with x % of Eu₂O₃ (x = 0.5, 1.0, 2.0, 4.0, and 8.0) by aqueous sol-gel synthesis method were also prepared. The thermal decomposition of both the La-Mo-O carbonate-tartrate and nitrate-tartrate gels, which is the critical stage of this preparation technique, is investigated in detail. X-ray diffraction, scanning electron microscopy, and ultraviolet-visible spectroscopy were used for the determination of crystal structure, surface morphology, and optical properties of the La-Mo-O:xEu₂O₃ samples annealed at 400, 500, 600, 700, 800, 900, and 1,000 °C temperatures, respectively. The obtained results show that the thermal decomposition of the La-Mo-O tartrate gel precursors has occurred in a separate manner. The differences that came up during the thermal treatment of La-Mo-O tartrate gels have related only with the initial composition that determined the different crystallization ways of final compounds. Besides, the dopant concentration mainly influences the size of obtained particles and agglomeration of synthesized final materials. The initial composition of the La-Mo-O gel precursors has significant influence on the formation of final crystal phases at relatively lower temperatures than was expected according to the TG-DTA measurements. Finally, the optical properties of La-Mo-O tartrate gel precursors annealed at 500 °C depend on the nature of the initial compounds, which were used during the aqueous sol-gel process.