SYNTHESIS, CHARACTERIZATION AND TUNABLE ELECTRONIC OPTICAL PROPERTIESOF II-VI SEMICONDUCTOR SPECIES INCLUDED IN THE SODALITE STRUCTURE/

The composition-dependent optical and electronic tunability of the sod alite analogues with stoichiometries Zn(8)X(2)[BO2](12) (X = O, S, Se) and [CdyZn(1-y)](8)X(2)[BeSixGe(1-x)O-4](6) (X = S, Se and Te) have b een demonstrated. The materials strongly photoluminesce, and a compari son of the photoluminescence behavior of tl-Le single crystals with th e as-synthesized powder analogues shows that the visible emission is i ntrinsic to the sodalite analogue and not due to impurities such as bu lk semiconductor. The emission maxima of these materials call be varie d by as much as 100 nm with subtle modifications in the host sodalite framework composition and excitation energies can be stored over, at m inimum, several minutes. The materials can be prepared either hydrothe rmally or by high-temperature solid-state reactions. The local and ave rage long-range structures of composition Zn(8)X(2)[BO2](12) (X = O, S , Se) and M(8)X(2)[BeSixGe1-xO4](6) (M = Zn, Cd; X = S, Se, Te) are de scribed based on the results of polycrystalline X-ray diffraction, mul tinuclear solid-state MAS NMR, CdL(3) XANES, UV/visible and photolumin escence spectroscopic measurements. Additionally, the crystal structur es of the synthetic helvite solid solutions Zn8S2[BeSixGe1-xO4](6) (x = 0.03, 0.37, 0.74) are presented based on refinement of single-crysta l 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) Angst rom, respectively. In all these sodalite analogues, the anionic, rigid sodalite framework encloses [M(4)X](6+) tetrahedra in a crystalline c ubic array, separating each tetrahedron from its eight nearest neighbo rs by at least 6.4 Angstrom, center to center. This electrostatic isol ation results in dramatic high-energy shifts in the optical absorption spectra of the materials and low-frequency shifts in the MAS NMR spec tra of the cage center anions, relative to the bulk semiconductors. Cd -113 MAS NMR and CdL(3) XANES spectra show that the influence of the a nion type on the electronic structure at the Cd2+ ions in the cadmium sodalites is small.