Rare earth fluorosulfides LnSF and Ln(2)AF(4)S(2) as new colour pigments

Rare earth fluorosulfides LnSF and Ln(2)AF(4)S(2) (A Ca, Sr) have been prep ared and characterized by X-ray diffraction. The structures can be describe d as the succession of various sheets of rare earth or alkaline earth, fluo rine and sulfur. Thus in these compounds, rare earth is at the center of a distorted square antiprism with four F atoms on one base, four S in the oth er and a fifth Ln-S bond parallel to the c axis. These compounds exhibit in teresting colour from yellow (Sm, Gd) to red (Ce). The chromatic properties have been correlated to structural features and mechanisms at the origin o f the colour have been proposed. The variation of energy of absorption edge as a function of rare earth has been explain in terms of ionization energi es. (C) 2001 Elsevier Science B.V. All rights reserved.