Yellow Pr-zircon pigments. The role of praseodymium and of the mineralizer

A sol–gel reaction starting from Si and Zr alkoxides, in water–ethanol mixtures, was employed to obtain praseodymium doped zirconium silicate powders (zircon). The reactions were performed by modulating both: (a) the amount of praseodymium salt in the starting mixture and (b) the speciation of the mineralizers; chloride and fluoride salts of monovalent (Na+, Li+) and divalent (Mg2+) were tested. The products of the sol–gel reaction were calcined either at 1000 ◦C or at 1200 ◦C. The samples were characterised by X-ray diffraction, SEM micrographs, EDX analyses and diffuse reflectance spectroscopy; the colour of the pigments was characterized on the grounds of the Commission Internationale de l’Eclairage (CIE) standard procedure (CIE L∗a∗b∗ measurements). Results from the structural, morphological and optical characterisations are examined and cross-compared to produce a consistent picture of the key factors leading to the formation, growth and optical properties of the reaction products.