Rare-Earth vs. Heavy Metal Pigments and their Colors from First Principles

摘要

Many inorganic pigments contain heavy metals hazardous to health andenvironment. Much attention has been devoted to the quest for non-toxicalternatives based on rare-earth elements. The computation of colors from firstprinciples is a challenge to electronic structure methods however, especiallyfor materials with localized f-orbitals. Here, starting from atomic positionsonly, we compute the color of the red pigment cerium fluorosulfide CeSF, aswell as of mercury sulfide HgS (classic "vermilion"). Our methodology employsmany-body theories to compute the optical absorption, combined with anintermediate length-scale modelization to assess how coloration depends on filmthickness, pigment concentration and granularity. We introduce a quantitativecriterion for the performance of a pigment. While for HgS this criterion issatisfied due to large transition matrix elements between wide bands, CeSFpresents an alternative paradigm: the bright red color is shown to stem fromthe combined effect of the quasi two-dimensionality and the localized nature of4f-states. Our work demonstrates the power of modern computational methods,with implications for the theoretical design of materials with specific opticalproperties.