New insight into the coloration mechanism and synthesis of ultrafine Pr-ZrSiO4 yellow pigments

It is of particular significance to unveil the authentic coloration mechanism of the multivalent praseodymium colored ZrSiO4 yellow pigments for advanced decoration applications. We herein adopted a facile strategy to modulate the fluorine-assisted zircon crystallization and thereby obtained ultrafine Pr-ZrSiO4 yellow pigments, which have a remarkably narrow size distribution and average diameters within 250-400 nm. By virtue of some cogent combinative spectra of reflection, absorption, excitation, and emission from three types of elaborately-designed H-2-, air-, and O-2-based pigments, the coloration mechanism for the Pr-colored zircon was systematically unveiled: both Pr4+ and Pr3+ coexist invariably in the pigments, while the former contributes primarily to the ligand-to-metal charge transfer from O-2p to Pr(IV)(4f) for the blue-violet absorption to generate the yellow hue, and the latter is inclined to discolor the pigments. Therefore, an oxidizing atmosphere is preferable to produce brilliant Pr-ZrSiO4 pigments with enhanced chromatic properties. The stark spectroscopic distinctions between the wide-band absorption from the nonluminescent tetravalency and the narrow-band absorption from the luminescent trivalency can expand our understanding to the rare-earth-based inorganic pigments.

Automated summary

In this study, ultrafine Pr-ZrSiO4 yellow pigments with a remarkably narrow size distribution were obtained by modulating the fluorine-assisted crystallization of zircon in a facile way. Through the comprehensive analysis of reflection, absorption, excitation, and emission spectra, the coloration mechanism of Pr-ZrSiO4 yellow pigments was systematically revealed. Both Pr4+ and Pr3+ coexisted in the pigments, with Pr4+ contributing primarily to the ligand-to-metal charge transfer and generating the yellow hue, while Pr3+ tended to discolor the pigments. Therefore, an oxidizing atmosphere is preferable for the production of brilliant Pr-ZrSiO4 pigments with enhanced chromatic properties.