Synthesis, Characterization and Tunable Electronic/Optical Properties of II−VI Semiconductor Species Included in the Sodalite Structure

Abstract

The composition-dependent optical and electronic tunability of the sodalite analogues with stoichiometries Zn8X2[BO2]12 (X = O, S, Se) and [Cd y Zn(1-y)]8X2[BeSi x Ge(1-x)O4]6 (X = S, Se and Te) have been demonstrated. The materials strongly photoluminesce, and a comparison of the photoluminescence behavior of the single crystals with the as-synthesized powder analogues shows that the visible emission is intrinsic to the sodalite analogue and not due to impurities such as bulk semiconductor. The emission maxima of these materials can be varied by as much as 100 nm with subtle modifications in the host sodalite framework composition and excitation energies can be stored over, at minimum, several minutes. The materials can be prepared either hydrothermally or by high-temperature solid-state reactions. The local and average long-range structures of composition Zn8X2[BO2]12 (X = O, S, Se) and M8X2[BeSi x Ge1-x O4]6 (M = Zn, Cd; X = S, Se, Te) are described based on the results of polycrystalline X-ray diffraction, multinuclear solid-state MAS NMR, CdL3 XANES, UV/visible and photoluminescence spectroscopic measurements. Additionally, the crystal structures of the synthetic helvite solid solutions Zn8S2[BeSi x Ge1-x O4]6 (x = 0.03, 0.37, 0.74) are presented based on refinement of single-crystal X-ray diffraction and selected area electron diffraction data; these materials crystallize in the acentric, cubic space group P23 (No. 195) with unit-cell parameters a = 8.250(4), 8.221(2), and 8.163(1) Å, respectively. In all these sodalite analogues, the anionic, rigid sodalite framework encloses [M4X]6+ tetrahedra in a crystalline cubic array, separating each tetrahedron from its eight nearest neighbors by at least 6.4 Å, center to center. This electrostatic isolation results in dramatic high-energy shifts in the optical absorption spectra of the materials and low-frequency shifts in the MAS NMR spectra of the cage center anions, relative to the bulk semiconductors. 113Cd MAS NMR and CdL3 XANES spectra show that the influence of the anion type on the electronic structure at the Cd2+ ions in the cadmium sodalites is small.

Reaction of Fully Indium-Exchanged Zeolite A with Hydrogen Sulfide. Crystal Structures of Indium-Exchanged Zeolite A Containing In2S, InSH, Sorbed H2S, and (In5)7+

“…On the 3-fold axes of each large cavity, 3.0 In + ions at In(1) and 0.5 In 3+ ions at In(8) lie opposite six-rings within the primary coordination spheres of framework oxygens, whereas 0.5 In + ions at In(10) are located deep in large cavity, probably as InSH molecules stabilized by sorbed H 2 S molecules and In + ions (see sections 4.3 and 4.4). On the 3-fold axes of each sodalite unit, 2.0 In 1.75+ ions at In (2) and 0.5 In + ions at In(3) are found opposite six-rings, as seen in previously reported crystal structures of In 11 -A and In 8.75 -A(S 2 ). 11,15 Near the eight-rings of each unit cell, a total of 2.5 more In + ions are found at three different Wyckoff positions (1.0, 0.5, and 1.0 at In(4), In (5), and In(9), respectively), where they are extensively involved in the stabilization of newly formed and sorbed molecules deep in large cavity (see sections 4.3 and 4.4).…”

“…As atoms, they may preferentially approach cations, to which they could delocalize electron density, rather than framework oxygens. Indeed, they are reasonably close to the indium cations at In (2) and In(3) in the sodalite units. These In 0 atoms at In(6) might have been retained during the reaction between In 0 and Tl-A, or might have been produced by disproportionation during later exposure to the atmosphere or to hydrogen sulfide, or both.…”

“…34 Finally, two In + ions at In(10) and a sulfur atom at S(1) comprise the In 2 S molecule formed by the above reaction; it is deep in the large cavity (see section 4.3). Each of the two In + ions in this In 2 S molecule is within a reasonable adsorption distances of S(2) (sorbed H 2 S molecules), forming a [(H 2 S)(InSIn)(H 2 S)] cluster which is in turn stabilized by approaches to two eight-ring In + ions at In(4) (see section (5): two eight-ring In + ions at In(4) and In(5) and three sorbed H2S molecules, one at S(1) and two at S (2). See the caption to Figure 1 for other details.…”

“…Various sulfide nanoclusters in zeolite cavities have shown unusual optical properties. [1][2][3][4][5][6][7][8][9][10][11] These are due to the quantum size effects of the nanoclusters and to the regular three-dimensional arrangements which the zeolite structure requires. ZnS and CdS clusters prepared in zeolite Y show an unusual blue shift in their absorption spectra, as compared to the bulk materials.…”

Synthesis of CdSe quantum dots with luminescence in the violet region of the solar spectrum

“…The synthesis conditions and reagents can be used to control the sizes and morphologies of nanoparticles. As a result, syntheses of monodispersed II-VI semiconductor nanoparticles have attracted a great deal of interest due to the potential applications of these nanoparticles as non-linear optical materials, [1] in devices, for biomedical imaging [2] and as photovoltaics. [3] There are many studies which have reported wet chemical syntheses of CdSe.…”