The dielectric function of LnSF rare-earth fluorosulfides ( Ln=La, Ce): experiment and theory

• Published in: Journal of solid state chemistry Vol. 177; no. 8; pp. 2833 - 2840
• Main Authors: Goubin, Fabrice, Rocquefelte, Xavier, Pauwels, Damien, Tressaud, Alain, Demourgues, Alain, Jobic, Stephane, Montardi, Yvan
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01.08.2004; Elsevier
• Subjects: Band structures; Chemical Sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Dielectric constants; Dielectric properties of solids and liquids; Dielectrics, piezoelectrics, and ferroelectrics and their properties; EELS; Exact sciences and technology; Lanthanide thiofluoride; Material chemistry; Optical properties; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Other nonmetallic inorganics; Other nonmetals; Permittivity (dielectric function); Physics; Visible and ultraviolet spectra; Band structures; Lanthanide thiofluoride; Optical properties; Dielectric constants; EELS; Band structure; Inorganic compounds; Ternary compounds; Refractive index; Digital simulation; Absorbers; Lanthanum fluorides; Rare earth compounds; Electronic density of states; Experimental study; Extinction index; Cerium fluorides; Dielectric function; EEL spectroscopy; Density functional method; Electronic transition; Absorption spectra
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2004.05.006

The absorption properties of LaSF and CeSF in the UV-Visible range have been investigated on the basis of first principles density functional theory (DFT) calculations and from electron energy-loss spectroscopy (EELS) measurements. The extinction coefficient k, as well as the refractive index n, determined experimentally from the loss function Im(−1/ ε), were compared with the corresponding factors extracted from the calculated dielectric tensor ε 2. The k and n values for the two compounds were expected to be very close to each other, owing to the chemical similarity of La and Ce. However, it was found that the nature of the electronic transitions in LaSF and CeSF strongly influences the k and n values with the result that the refractive index n and the extinction coefficient k are substantially larger for LaSF than for CeSF.