Phase formation in LaF3–NaGdF4, NaGdF4–NaLuF4, and NaLuF4–NaYF4 systems: Synthesis of powders by co-precipitation from aqueous solutions

Abstract Detailed studies of LaF 3 –NaGdF 4 , NaGdF 4 –NaLuF 4 , and NaLuF 4 –NaYF 4 systems have revealed that LaF 3 –NaGdF 4 system precipitates, formed in aqueous media, contained gagarinite-type NaGd 1− x La x F 4 ( x  ≤ 0.0625) solid solution, tysonite-type La 1− x Gd x F 3 ( x  ≤ 0.50) phase, and cubic fluorite-type NaGdF 4 -based phase, whereas NaGdF 4 –NaLuF 4 precipitates contained hexagonal gagarinite-type ( x  ≤ 0.25) and cubic fluorite-type ( x  ≥ 0.675) NaGd 1− x Lu x F 4 solid solutions. Furthermore, there were continuous series of single-phase cubic fluorite-type NaLuF 4 –NaYF 4 solid solutions formed in the third investigated system. Crystallization of Na 0.5− x Lu 0.5+ x F 2+2 x solid solutions from aqueous media occurred in an incongruent manner; the use of 5-fold excess of NaF led to precipitation of NaLuF 4 ( x  = 0) with almost stoichiometric composition.