Doping is a widely applied technological process in materials science that involves incorporating atoms or ions of appropriate elements into host lattices to yield hybrid materials with desirable properties and functions. For nanocrystalline materials, doping is of fundamental importance in stabilizing a specific crystallographic phase, modifying electronic properties, modulating magnetism as well as tuning emission properties. Here we describe a material system in which doping influences the growth process to give simultaneous control over the crystallographic phase, size and optical emission properties of the resulting nanocrystals. We show that NaYF(4) nanocrystals can be rationally tuned in size (down to ten nanometres), phase (cubic or hexagonal) and upconversion emission colour (green to blue) through use of trivalent lanthanide dopant ions introduced at precisely defined concentrations. We use first-principles calculations to confirm that the influence of lanthanide doping on crystal phase and size arises from a strong dependence on the size and dipole polarizability of the substitutional dopant ion. Our results suggest that the doping-induced structural and size transition, demonstrated here in NaYF(4) upconversion nanocrystals, could be extended to other lanthanide-doped nanocrystal systems for applications ranging from luminescent biological labels to volumetric three-dimensional displays.

Simultaneous phase and size control of upconversion nanocrystals through lanthanide doping

Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

The controllable synthesis of nanostructured CeO2-based materials is an imperative issue for environment- and energy-related applications. In this review, we present the recent technological and theoretical advances related to the CeO2-based nanomaterials, with a focus on the synthesis from one dimensional to mesoporous ceria as well as the properties from defect chemistry to nano-size effects. Seven extensively studied aspects regarding the applications of nanostructured ceria-based materials are selectively surveyed as well. New experimental approaches have been demonstrated with an atomic scale resolution characterization. Density functional theory (DFT) calculations can provide insight into the rational design of highly reactive catalysts and understanding of the interactions between the noble metal and ceria support. Achieving desired morphologies with designed crystal facets and oxygen vacancy clusters in ceria via controlled synthesis process is quite important for highly active catalysts. Finally, remarks on the challenges and perspectives on this exciting field are proposed.

Nanostructured ceria-based materials: synthesis, properties, and applications

Researchers are intensively investigating photochemical water splitting as a means of converting solar to chemical energy in the form of fuels. Hydrogen is a key solar fuel because it can be used directly in combustion engines or fuel cells, or combined catalytically with CO2 to make carbon containing fuels. Different approaches to solar water splitting include semiconductor particles as photocatalysts and photoelectrodes, molecular donor-acceptor systems linked to catalysts for hydrogen and oxygen evolution, and photovoltaic cells coupled directly or indirectly to electrocatalysts. Despite several decades of research, solar hydrogen generation is efficient only in systems that use expensive photovoltaic cells to power water electrolysis. Direct photocatalytic water splitting is a challenging problem because the reaction is thermodynamically uphill. Light absorption results in the formation of energetic charge-separated states in both molecular donor−acceptor systems and semiconductor particles. Unfortuna...

https://faculty.missouri.edu/~glaserr/3700s13/SolarCells_HER_Mallouck_ar9002398.pdf

Visible Light Water Splitting Using Dye-Sensitized Oxide Semiconductors

Crystal facet engineering of semiconductor photocatalysts: motivations, advances and unique properties

Ceria nanoparticles are one of the key abrasive materials for chemical-mechanical planarization of advanced integrated circuits. However, ceria nanoparticles synthesized by existing techniques are irregularly faceted, and they scratch the silicon wafers and increase defect concentrations. We developed an approach for large-scale synthesis of single-crystal ceria nanospheres that can reduce the polishing defects by 80% and increase the silica removal rate by 50%, facilitating precise and reliable mass-manufacturing of chips for nanoelectronics. We doped the ceria system with titanium, using flame temperatures that facilitate crystallization of the ceria yet retain the titania in a molten state. In conjunction with molecular dynamics simulation, we show that under these conditions, the inner ceria core evolves in a single-crystal spherical shape without faceting, because throughout the crystallization it is completely encapsulated by a molten 1- to 2-nanometer shell of titania that, in liquid state, minimizes the surface energy. The principle demonstrated here could be applied to other oxide systems.

https://science.sciencemag.org/content/sci/312/5779/1504.full.pdf

Converting Ceria Polyhedral Nanoparticles into Single-Crystal Nanospheres

Synthesis of mixed copper-indium chalcogenolates. Single-source precursors for the photovoltaic materials CuInQ2 (Q = S, Se)

Multilayer thin films consisting of anionic α-zirconium phosphate (α-ZrP) sheets, tetrameric zirconium hydroxide cations [Zr4(OH)8(H2O)16]8+ (Zr48+), and alkanediylbis(phosphonic acid) (CnBPA) have been grown on silicon and gold surfaces by sequential adsorption reactions. The thin films were characterized by ellipsometry, X-ray diffraction, reflectance infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Alternately dipping cationic substrates into exfoliated α-ZrP-containing suspensions, aqueous zirconium oxychloride, and ethanolic C16BPA solutions generates a mixed ionic/covalent multilayer structure. The tetrameric Zr48+ cation adsorbs onto the α-ZrP surface, providing a covalent anchoring point for the growth of the C16BPA layer. Adsorbing a second layer of zirconium ions onto the C16BPA layer allows one to continue the layer growth sequence using either covalent (metal/phosphonate) or ionic (α-ZrP/polycation) interlayer connections. A multilayer film with...

A “Mix and Match” Ionic−Covalent Strategy for Self-Assembly of Inorganic Multilayer Films

From the reaction of elemental copper and either lanthanides or actinides in molten alkali metal/polychalcogenide salts, several new quaternary phases have been discovered. Specifically, these phases are ACuM2Q6 (where A = K, M = La, Q = S; A = Cs, M = Ce, Q = S; or A = K, M = Ce, Q = Se) and ACuMQ3 (where A = Cs, M = Ce, Q = S; or A = K, M = U, Q = Se). The CsCuCe2S6 crystallizes in the orthorhombic space group Immm with a = 5.500(1) A, b = 22.45(1) A, c = 4.205(4) A. The KCuCe2Se6 is isostructural. The CsCuCeS3 crystallizes in the orthorhombic space group Cmcm with a = 4.024(2) A, b = 15.154(2) A, c = 10.353(3) A. The KCuUSe3 is isostructural. In ACuM2Q6, the lanthanides bond to a mixture of mono- and disulfides in a bicapped trigonal prismatic geometry; these polyhedra subsequently connect in two dimensions, forming layers equivalent to those seen in the ZrSe3 structure type with Cu+ atoms residing in tetrahedral sites within the layers and alkali cations in the interlayer gallery. The compounds of the...

/pdf/new-quaternary-compounds-resulting-from-the-reaction-of-krrrpyoexq.pdf

New quaternary compounds resulting from the reaction of copper and f-block metals in molten polychalcogenide salts at intermediate temperatures. Valence fluctuations in the layered CsCuCeS3

Anthony C. Sutorik

Papers

Converting Ceria Polyhedral Nanoparticles into Single-Crystal Nanospheres

Synthesis of mixed copper-indium chalcogenolates. Single-source precursors for the photovoltaic materials CuInQ2 (Q = S, Se)

A “Mix and Match” Ionic−Covalent Strategy for Self-Assembly of Inorganic Multilayer Films

New quaternary compounds resulting from the reaction of copper and f-block metals in molten polychalcogenide salts at intermediate temperatures. Valence fluctuations in the layered CsCuCeS3

The Application of Polychalcogenide Salts to the Exploratory Synthesis of Solid State Multinary Chalcogenides at Intermediate Temperatures