Quantum Dots of [Na4 Cs6 PbBr4 ]8+ , Water Stable in Zeolite X, Luminesce Sharply in the Green.

Nanocrystals (NCs) of CsPbX3 , X = Cl, Br, or I, have excellent photoluminescent properties: high quantum yield, tunable emission wavelengths (410-700 nm), and narrow emission band widths. CsPbBr3 NCs show high promise as a green-emitting material for use in wide color gamut displays. CsPbBr3 NCs have, however, not been commercialized because they are sensitive to moisture and heat. To avoid these problems, this work attempts to introduce CsPbBr3 into five zeolites. The zeolite X product, Pb,Br,H,Cs,Na-X, shows superior stability toward moisture, maintaining its initial luminescence properties after being under water for more than a month. Its structure, determined using single-crystal X-ray crystallography, shows that quantum dots (QDs) of [Na4 Cs6 PbBr4 ]8+ (not of CsPbBr3 ) have formed. They are tetrahedral PbBr4 2- ions (Pb-Br = 3.091(11) Å) surrounded by Na+ and Cs+ ions. Each fills the zeolite's supercage with its Pb2+ ion precisely at the center, a position of high symmetry. The peaks in the emission spectra of Pb,Br,H,Cs,Na-X and the CsPbBr3 NCs are both at about 520 nm. The FWHM of Pb,Br,H,Cs,Na-X, however, is narrower than any previously reported for any of the CsPbBr3 NCs, and for zeolite Y and the various mesoporous materials treated with CsPbBr3 .

Giant Electron-Phonon Coupling and Deep Conduction Band Resonance in Metal Halide Double Perovskite.

The room-temperature charge carrier mobility and excitation-emission properties of metal halide perovskites are governed by their electronic band structures and intrinsic lattice phonon scattering mechanisms. Establishing how charge carriers interact within this scenario will have far-reaching consequences for developing high-efficiency materials for optoelectronic applications. Herein we evaluate the charge carrier scattering properties and conduction band environment of the double perovskite Cs2AgBiBr6 via a combinatorial approach; single crystal X-ray diffraction, optical excitation and temperature-dependent emission spectroscopy, resonant and nonresonant Raman scattering, further supported by first-principles calculations. We identify deep conduction band energy levels and that scattering from longitudinal optical phonons- via the Fröhlich interaction-dominates electron scattering at room temperature, manifesting within the nominally nonresonant Raman spectrum as multiphonon processes up to the fourth order. A Fröhlich coupling constant nearing 230 meV is inferred from a temperature-dependent emission line width analysis and is found to be extremely large compared to popular lead halide perovskites (between 40 and 60 meV), highlighting the fundamentally different nature of the two "single" and "double" perovskite materials branches.

Preparation, crystal structure, and thermal stability of the cadmium sulfide nanoclusters Cd6S44+ and Cd2Na2S4+in the sodalite cavities of zeolite A (LTA).

The crystal structure and thermal stability of two cadmium sulfide nanoclusters prepared in zeolite A (LTA) have been studied by XPS, TGA, and single-crystal and powder XRD. The crystal structures of Cd2.4Na3.2(Cd6S4)0.4(Cd2Na2S)0.6(H2O)> or =5.8[Si12Al12O48]-LTA (a = 12.2919(7) A, crystal 1 (hydrated)) and /Cd4Na2(Cd2O)(Na2O)/[Si12Al12O48]-LTA (a = 12.2617(4) A, crystal 2 (dehydrated)) were determined by single-crystal methods in the cubic space group Pm3m at 294(1) K. Crystal 1 was prepared by ion exchange of Na12-LTA in an aqueous stream 0.05 M in Cd2+, followed by washing in a stream of water, followed by reaction in an aqueous stream 0.05 M in Na2S. Crystal 2 was made by dehydrating crystal 1 at 623 K and 1 x 10(-6) Torr for 3 days. In crystal 1, Cd6S4(4+) nanoclusters were found in and extending out of about 40% of the sodalite cavities. Central to each Cd6S4(4+) cluster is a Cd4S4 unit (interpenetrating Cd2+ and S2- tetrahedra with near Td symmetry, Cd-S = 2.997(24) A, Cd-S-Cd = 113.8(12) degrees, and S-Cd-S = 58.1(24) degrees). Each of the two remaining Cd2+ ions bonds radially through a 6-ring of the zeolite framework to a sulfide ion of this Cd4S4 unit (Cd-S = 2.90(8) A). In each of the remaining 60% of the sodalite cavities of crystal 1, a planar Cd2Na2S4+ cluster was found (Cd-S/Na-S = 2.35(5)/2.56(14) A and Cd-S-Cd/Na-S-Na = 122(5)/92(7) degrees). Cd6S4(4+) and Cd2Na2S4+ are stable within the zeolite up to about 700 K in air. Upon vacuum dehydration at 623 K, all sulfur was lost (crystal 2). Instead as anions, only two oxide ions remain per sodalite unit. One bridges between two Cd2+ ions (Cd2O2+, Cd-O = 2.28(3) A) and the other between two Na+ ions (Na2O, Na-O = 2.21(10) A).

Characteristics of nitrogen release from synthetic zeolite Na-P1 occluding NH4NO3.

Zeolites can accommodate a considerable amount of occluded salt such as NH4NO3, which can serve as a good source of slow-release plant nutrient. This study evaluates the kinetics of ion release from NH4NO3-occluded Na-P1 (N-NaP) using a simulated soil solution and deionized water as leaching solutions. The patterns of ion releases were examined as a function of leaching time under both static and continuous-flow conditions for more than one month. Releases of both NH4+ and NO3- from N-NaP were found to be slow and steady under both the above conditions. The soil solution affected the release of NH4+ and NO3- differently, while deionized water released nearly the same equivalents of these ions. This clearly indicates that ion release from salt-occluded zeolite involves two different reactions, cation exchange and dissolution. The kinetics of ion release from occluded NH4NO3 under static condition was best described by the standard Elovich model while the power function model best expressed these under continuous-flow condition. The initial ion release patterns under both conditions exhibited considerable deviation from the simulated models, probably as a result of the presence of hydrated occluded NH4NO3. Flow condition and the presence of electrolytes in leaching solution affected the release kinetics significantly. Release of occluded NH4NO3 was delayed by the presence of the NH4NO3 coated on zeolite crystals. These results indicate that the ion release property of occluded salt could be predicted and controlled. This study clearly shows that NH4NO3-occluded zeolites could be developed as slow release fertilizers.

Facile palladium-catalysed synthesis of 1-aryl-1H-indazoles from 2-bromobenzaldehydes and arylhydrazines.

2-Bromobenzaldehydes react with arylhydrazines in toluene at 100 [degree]C in the presence of a catalytic amount of a palladium catalyst and phosphorus chelating ligands such as 1,1[prime or minute]-bis(diphenylphosphino)ferrocene and 1,3-bis(diphenylphosphino)propane along with NaO-t-Bu to afford 1-aryl-1H-indazoles in good yields.