Synthesis of a Series of Rare-Earth-based Multi Anion Chalcogenide Iodides: RE3Si2SexS8-xI (RE = La, Ce, Pr, and Nd) Flux-Assisted Boron Chalcogen Mixture Method Crystal Growth and Characterization of Magnetic, Optical, and Photoluminescent Properties

Abstract

Single crystals and polycrystalline powders of rare earth mixed chalcogenide iodides La3Si2Se1.21S6.79I, Ce3Si2Se1.39S6.61I, Pr3Si2Se1.22S6.78I, and Nd3Si2Se1.18S6.82I, were prepared using the reactive flux-assisted boron chalcogen mixture (BCM) method at 850 C. All compounds crystallized in the monoclinic crystal system, space group C2/c (space group number 15). The series adopts the La3Si2O8Cl structure-type, containing isolated SiQ4 tetrahedra connected by REQ8 (RE = La, Ce, Pr and Nd) polyhedra; this arrangement creates tunnels that are filled by the I atoms. The partial substitution of S by Se was carried out to modulate the optical properties. Phase pure samples and uniform solid solutions were obtained for all compositions as determined by powder X-ray diffraction patterns. Polycrystalline powders were used for physical property measurements, including magnetic susceptibility and UV-Vis diffuse reflectance. The solid-state UV-vis data for the polycrystalline La3Si2Se1.21S6.79I, Ce3Si2Se1.39S6.61I, and Pr3Si2Se1.22S6.78I samples revealed bandgap of Eg = 2.5(1) eV, Eg = 2.2(1) eV, and Eg = 2.3(1) eV, typical for semiconductor. Magnetic measurements indicated that Ce3Si2Se1.39S6.61I and Nd3Si2Se1.18S6.82I exhibits paramagnetic behavior with slightly negative Weiss constant,  = -38 and  = -25. The photoluminescence spectrum of Ce3Si2Se1.39S6.61I exhibits a broad emission band around ∼493 nm.