The CsLnMSe₃ Semiconductors (Ln = Rare-Earth Element, Y; M = Zn, Cd, Hg)

Abstract

CsLnCdSe(3) (Ln = Ce, Pr, Sm, Gd, Tb, Dy, Y) and CsLnHgSe(3) (Ln = La, Ce, Pr, Nd, Sm, Gd, Y) have been synthesized at 1123 K. These isostructural materials crystallize in the layered KZrCuS(3) structure type in the orthorhombic space group Cmcm and are group X extensions of the previously characterized Zn compounds. The structure is composed of two-dimensional [LnMSe(3)] layers that stack perpendicular to [010] and are separated by layers of face- and edge-sharing CsSe(8) bicapped trigonal prisms. Because there are no Se-Se bonds in the structure of CsLnMSe(3) (M = Zn, Cd, Hg), the formal oxidation states of Cs/Ln/M/Se are 1+/3+/2+/2-. CsSmHgSe(3) does not adhere to the Curie-Weiss law, whereas CsCeHgSe(3) and CsGdHgSe(3) are Curie-Weiss paramagnets with micro (eff) values of 2.77 and 7.90 micro (B), corresponding well with the theoretical values of 2.54 and 7.94 micro (B) for Ce(3+) and Gd(3+), respectively. Single-crystal optical absorption measurements were performed with polarized light perpendicular to the (010) and (001) crystal faces of these materials. The band gaps of the (010) crystal faces range from 1.94 eV (CsCeHgSe(3)) to 2.58 eV (CsYCdSe(3)) whereas those of the (001) crystal faces span the range 2.37 eV (CsSmHgSe(3)) to 2.54 eV (CsYCdSe(3) and CsYHgSe(3)). The largest band gap variation between crystal faces is 0.06 eV for CsYCdSe(3). Theoretical calculations for CsYMSe(3) indicate that these materials are direct band gap semiconductors whose colors and optical band gaps are dependent upon the orbitals of Y, M, and Se.

Synthesis, structure, optical properties, and electronic structure of NaLiCdS2

“…4c. The intersection of the least-squares lines of baseline and band edge [28] lead to an optical band gap of 2.37 eV. This value is consistent with the reddish-yellow color of the compound and agrees well with theory.…”

“…Electronic structure calculations indicate that NaLiCdS 2 is semiconducting (see below). In order to determine the nature of the transition at about 2.4 eV the scaled absorption value and the crystal thickness were used to calculate the absorption coefficient a [28]. Plots of (ahn) 2 vs. hn (Fig.…”

“…The Na, Li, Cd, and S orbitals are highly overlapped in the valence band and the conduction band, which can be seen from the overlap among them around the Fermi level. The heavier alkali metals (Cs, Rb, K) usually make no contributions around the Fermi level and hence exert almost no effects on the electronic structures of comparable compounds, for example KSm 2 CuS 4 [31], RbLnSe 2 [32], and CsLnMSe 3 (M ¼ Zn, Cd, Mn) [28]. However, in NaLiCdS 2 the contributions of the Na 3s electrons around the Fermi level, and thus to the electronic structure, cannot be ignored.…”

Sn2SiS4, synthesis, structure, optical and electronic properties

“…4. Based on the diffuse reflectance measurement and the electronic structure calculation, the Sn 2 SiS 4 should possess an indirect band gap of about 2.00 eV [41,42].…”

Syntheses, Crystal Structures, and Optical and Magnetic Properties of Some CsLnCoQ3 Compounds (Ln = Tm and Yb, Q = S; Ln = Ho and Yb, Q = Se)

“…Both from experiment and first-principles electronic structure calculations, it is found that the band gaps of the ALnMQ 3 materials (A ϭ Rb, Cs; Ln ϭ rare-earth metal; M ϭ Mn, Zn, Cd, Hg) can be tuned through simple chemical substitution of Ln, M, or Q [5Ϫ7]. For some of these compounds, there is also a slight dependence of band gap on crystal orientation [5,8]. Most of these compounds show Curie-Weiss behavior [7], except for the compounds Ln ϭ Yb/M ϭ Mn, Zn that show magnetic transitions at temperatures below ϳ10 K. Thus these ALnMQ 3 compounds are a new class of magnetic semiconductors with tunable band gaps that show potential applications in magnetic storage devices [9,10] and photonic devices such as optical waveguides [11], optical filters [12], spontaneous emitters [13], and photon traps [14].…”