Controlling the Luminescence of Rare-Earth Chalcogenide Iodides RE₃(Ge_1–xSi_x)₂S₈I (RE = La, Ce, and Pr) and Ce₃Si₂(S_1–ySe_y)₈I

Abstract

a r t h c h a l c o g e n i d e i o d i d e s RE 3 (Ge 1−x Si x ) 2 S 8 I (RE = La, Ce, and Pr) and Ce 3 Si 2 (S 1−y Se y ) 8 I were prepared by reactions of the elements at 900 °C. Phase-pure samples and complete solid solutions were obtained for all series, as determined by powder X-ray diffraction patterns, with the cell parameters evolving smoothly. They adopt the monoclinic La 3 Si 2 O 8 Cl-type structure (space group C2/c), containing isolated tetrahedra centered by the tetrel atoms and separated by the RE and I atoms. Single-crystal X-ray diffraction studies indicate that substitution of Si for Ge atoms in RE 3 (Ge 1−x Si x ) 2 S 8 I leads to complete disorder of the tetrel atoms, whereas partial substitution of Se for S atoms in Ce 3 Si 2 (S 1−y Se y ) 8 I occurs with preferential occupation of Se atoms. The optical band gaps increase slightly upon substitution with Si in RE 3 (Ge 1−x Si x ) 2 S 8 I (or negligibly in the case of the Ce-containing series, remaining at 2.8 eV), and they decrease dramatically upon substitution with Se in Ce 3 Si 2 (S 1−y Se y ) 8 I, from 2.8 to 1.9 eV. These band gaps are direct according to electronic structure calculations. The strong blue photoluminescence emission in Ce 3 Si 2 S 8 I shifts slightly to blue-green in Ce 3 (Ge 0.25 Si 0.75 ) 2 S 8 I and significantly to green in Ce 3 Si 2 (S 0.81 Se 0.19 ) 8 I, as quantified by their chromaticity coordinates. Increasing the concentration of Ge or Se tends to decrease the photoluminescence intensity and lifetime. For Ce 3 Si 2 S 8 I, the activation energy for thermal quenching is 0.68 eV.

Are Selenides the Same as Sulfides? Structure, Spectroscopy, and Properties of Narrow-Gap Rare-Earth Semiconductors RE2Sn(S1–xSex)5 (RE = La, Ce; x = 0–0.8)

“…13 Careful single-crystal structure determinations reveal that the S and Se atoms are not necessarily randomly distributed, but often exhibit pronounced preference for specific sites when several are available to be occupied, as observed in LaS 2−x Se x , 14−16 La 3 USe 3 S 2 , 17 and Ce 3 Si 2 (S 1−x Se x ) 8 I. 13 This phenomenon is generalizable to other mixed chalcogenides such as TlCr 5 S 8−x Se x . 18 Within the RE−Sn−S systems, the most prevalent ternary phases are RE 2 SnS 5 (RE = La−Nd, Sm, Gd−Dy).…”

“…Combined with the tunability offered by introducing RE components with different sizes and numbers of unpaired electrons, these mixed chalcogenides allow physical properties to be controlled in multiple ways. Substitutions in the chalcogen component can lead to structural changes (Sm 2 S 2– x Se 1+ x ), magnetic ordering [EuSe 1– x S x , Eu x Sr 1– x S y Se 1– y , BaLa 2 Co­(S 1– x Se x ) 5 ], − valence fluctuation (TmS 1– x Se x ), emergence of superconductivity (Eu 0.5 La 0.5 BiS 2– x Se x F), improved thermoelectric properties (LaBiS 2– x Se x O), and shifts in photoluminescence emission wavelength (Ce 3 Si 2 (S 1– x Se x ) 8 I) . Careful single-crystal structure determinations reveal that the S and Se atoms are not necessarily randomly distributed, but often exhibit pronounced preference for specific sites when several are available to be occupied, as observed in LaS 2– x Se x , − La 3 USe 3 S 2 , and Ce 3 Si 2 (S 1– x Se x ) 8 I .…”

“…Substitutions in the chalcogen component can lead to structural changes (Sm 2 S 2– x Se 1+ x ), magnetic ordering [EuSe 1– x S x , Eu x Sr 1– x S y Se 1– y , BaLa 2 Co­(S 1– x Se x ) 5 ], − valence fluctuation (TmS 1– x Se x ), emergence of superconductivity (Eu 0.5 La 0.5 BiS 2– x Se x F), improved thermoelectric properties (LaBiS 2– x Se x O), and shifts in photoluminescence emission wavelength (Ce 3 Si 2 (S 1– x Se x ) 8 I) . Careful single-crystal structure determinations reveal that the S and Se atoms are not necessarily randomly distributed, but often exhibit pronounced preference for specific sites when several are available to be occupied, as observed in LaS 2– x Se x , − La 3 USe 3 S 2 , and Ce 3 Si 2 (S 1– x Se x ) 8 I . This phenomenon is generalizable to other mixed chalcogenides such as TlCr 5 S 8– x Se x …”

Crystal Growth of Quaternary AkRE2Si2S8 (Ak = Ca and Sr; RE = La–Tb) Thiosilicates Using Flux-Assisted Boron Chalcogen Mixture Method: Exploring X-ray Scintillation, Luminescence, and Magnetic Properties

“…Complex metal chalcogenides are well-known for their structural diversity and extensive physical properties and, consequently, their synthesis has been widely explored. − As a class, chalcogenides are more polarizable than oxides and also exhibit a tendency to self-catenate, often leading to relatively complex structures that exhibit interesting electronic structures and functionalities. , Lanthanide-containing chalcogenides, in particular, have garnered attention for their capacity to form intricate ternary and quaternary compounds, as have many main group and transition element-containing compositions. These novel structures of metal chalcogenides have paved the way for numerous applications, including thermoelectrics, photovoltaics, optics, optoelectronics, magnetism, photoluminescence, nonlinear optics, and scintillation …”