A rare-earth phosphor containing one-dimensional chains identified through combinatorial methods

Magnetization-structure-composition phase diagram mapping in Co-Fe-Ni alloys using diffusion multiples and scanning Hall probe microscopy

Transition metal alloys are essential for magnetic recording, memory, and new materials-by-design applications. Saturation magnetization in these alloys have previously been measured by conventional techniques, for a limited number of samples with discrete compositions, a laborious and time-consuming effort. Here, we propose a method to construct complete saturation magnetization diagrams for Co–Fe–Ni alloys using scanning Hall probe microscopy (SHPM). A composition gradient was created by the diffusion multiple technique, generating a full combinatorial materials library with an identical thermal history. The composition and crystallographic phases of the alloys were identified by integrated energy dispersive X-ray spectroscopy and electron backscatter diffraction. “Pixel-by-pixel” perpendicular components of the magnetic field were converted into maps of saturation magnetization using the inversion matrix technique. The saturation magnetization dependence for the binary alloys was consistent with the Slater-Pauling behavior. By using a significantly denser data point distribution than previously available, the maximum of the Slater-Pauling curve for the Co–Fe alloys was identified at ~ 32 at% of Co. By mapping the entire ternary diagram of Co–Fe–Ni alloys recorded in a single experiment, we have demonstrated that SHPM—in concert with the combinatorial approach—is a powerful high-throughput characterization tool, providing an effective metrology platform to advance the search for new magnetic materials.

Understanding the role of fuels and impure phases on photoluminescence and thermoluminescence properties of combustion-derived nano Sr2 CeO4 blue light-emitting phosphor

Despite great advancements in optical materials and luminescent hosts, self-luminescent blue-emitting phosphors are very limited. In this study we present the influence of fuels used in combustion synthesis on the photoluminescence and thermoluminescence (TL) characteristics of self-luminescent Sr₂ CeO₄ blue-emitting phosphors. Four different fuels, oxalyldihydrazide (ODH), sugar, glycine, and ethylenediaminetetraacetic acid, were used to synthesize Sr₂ CeO_4. Powder X-ray diffraction patterns showed that pure orthorhombic Sr₂ CeO₄ was formed only with the ODH fuel and the other fuels resulted in the formation of impurity phases. Excitation spectra showed peaks at ~290 and 340 nm, corresponding to charge transfer bands from different O₂ ^- to Ce⁴⁺ ions. The emission spectra showed an intense blue-emitting band at 470 nm and the highest emission intensity was found for the sample prepared with ODH. Furthermore, TL glow curves for the γ-irradiated Sr₂ CeO₄ nanophosphor showed that ODH as fuel produced a more intense glow curve compared with other fuels investigated. TL glow curve analysis was carried out by calculating parameters such as activation energy, frequency factor, and order of kinetics. This study explores the importance and role of fuel in tuning the optical properties of phosphor hosts.

Studies of graphene influence on the laser induced white emission spectra of Sr2CeO4/graphene flake composites

The Stokes and anti-Stokes emission spectra generated from Sr2CeO4/graphene flake composites were investigated. The excitation and emission spectra, decay profiles and quantum efficiency of the studied materials were collected. It was found that the addition of graphene flakes (GFs) significantly affects spectroscopic properties. In particular, the anti-Stokes laser induced white emission spectra were analyzed as a function of excitation laser power, and ambient atmospheric pressure. The influence of graphene flakes concentration on laser induced photocurrent was investigated. The color of their emission significantly differs from the color of other tested composites. In particular, the impact of graphene concentration on the investigated features will be presented and mechanisms responsible for the observed effects will be discussed.

Dye doped concentric shell nanoparticles for enhanced photophysical performance of downconverting light emitting diodes

In this study, we examined the potential for perylene dye doped nanoparticles to enhance Light Emitting Diodes (LED) efficacy by minimizing π-π intermolecular aggregation, and enhancing photoluminescence and photostability of the dye molecules in the solid state. Towards this end, we encapsulated perylene dyes, suitably modified with a reactive silica precursor, into silica nanoparticles within a silica-dye-silica concentric layered shell. We found that the fluorescent yield was higher when the dye was embedded in a buried concentric shell within the silica nanoparticles (NPs) compared to an undoped shell/dye doped core nanoparticle morphology or unencapsulated dye with the same net dye concentration in solution. A strong dependence of relative quantum yield on dye doping concentration in the silica-dye-silica nanoparticles was observed. The uniform ∼ 100 nm large silica-dye-silica layered nanoparticles were used to prepare transparent dye doped silica nanoparticle/silicone nanocomposites. Dye doped silica nanoparticle/silicone nanocomposites exhibited higher photostability than the unencapsulated dye samples during long time aging tests under a blue LED with a wavelength of 455 nm at 300 ± 3% mA for 24 h. Novel dye doped layered silica NPs and their nanocomposites offer scope for developing organic luminescent materials into efficient and color-tunable light emitters for low-cost display, lighting, and optical communication applications.

Luminescent perovskites: recent advances in theory and experiments

This review summarizes previous research on luminescent perovskites, including oxides and halides, with different structural dimensionality. The relationship between the crystal structure, electronic structure and properties is discussed in detail.

Ce4+-Based Compounds Capable of Photoluminescence by Charge Transfer Excitation under Near-Ultraviolet-Visible Light

Ce⁴⁺-based charge transfer phosphor is not common and has been reported mainly in Sr₂CeO₄ with an excitation band peaking at ∼290 nm, mismatching with the near-ultraviolet light emitting diodes. Herein, we report a new series of Ce⁴⁺-based compounds Sr_4.4Ce_2.6REZnO₁₂ (RE = Y, La, and Eu) capable of photoluminescence induced by O^2--Ce⁴⁺ charge transfer excitation under near-ultraviolet-visible light. The crystal structure of Sr_4.4Ce_2.6EuZnO₁₂ was determined by single crystal X-ray diffraction. The RE = La and Y samples were confirmed to be iso-structure compounds of the RE = Eu sample by powder X-ray diffraction. By introducing highly covalent Zn²⁺-O^2- bonds into the framework, the Ce⁴⁺-O^2- bonds are lengthened due to the effect of the Ce⁴⁺-O^2--Zn²⁺ stretch. The lengthened Ce⁴⁺-O^2- bond weakens the repulsion of the electrons between Ce⁴⁺ and O^2-, thereby lowering the charge transfer energy to the visible light region. Incorporation of Eu³⁺ into the present compounds realized red emission under near-ultraviolet-visible excitation by the O^2--Ce⁴⁺ charge transfer followed by energy transfer to Eu³⁺.

Method for the Detailed Characterization of Cosputtered Inorganic Luminescent Material Libraries

Understanding the behavior of combinatorially developed luminescent materials requires detailed characterization methods that have been lacking thus far. We developed a device for directly surveying the luminescent properties of thin-film libraries created through combinatorial gradient sputter deposition. Step-scan recorded excitation-, emission- and luminescence decay spectra of a thin-film library were resolved and combined with EDX measurements on the same film, relating composition to luminescent properties. This technique was applied to a single-substrate gradient thin-film library of NaBr_0.73I_0.27 to NaBr_0.09I_0.91, doped with 6.5% to 16.5% Eu²⁺. This gradient film closely followed Vegard’s law, with emission fluently shifting from 428 to 439 nm. In comparison, pure NaBr:Eu²⁺ showed emission at 428 nm and NaI:Eu²⁺ at 441 nm. Luminescence decay measurements demonstrated a great degree of concentration quenching in the gradient film. From these measurements we could conclude that an optimized phosphor would most efficiently luminesce when close to NaI:Eu²⁺. This gradient film confirmed that the method presented in this work allows to both study and optimize luminescent behavior in a broad range of host- and dopant systems.

High-Throughput Synthesis and Characterization of Eu Doped Ba xSr2- xSiO4 Thin Film Phosphors

High-throughput techniques have been employed for the synthesis and characterization of thin film phosphors of Eu-doped Ba _xSr_{2- x}SiO₄. Direct synthesis from evaporation of the constituent elements under a flux of atomic oxygen on a sapphire substrate at 850 °C was used to directly produce thin film libraries (415 nm thickness) of the crystalline orthosilicate phase with the desired compositional variation (0.24 > x > 1.86). The orthosilicate phase could be synthesized as a pure, or predominantly pure, phase. Annealing the as synthesized library in a reducing atmosphere resulted in the reduction of the Eu while retaining the orthosilicate phase, and resulted in a materials thin film library where fluorescence excited by blue light (450 nm) was observable by the naked eye. Parallel screening of the fluorescence from the combinatorial libraries of Eu doped Ba _xSr_{2- x}SiO₄ has been implemented by imaging the fluorescent radiation over the library using a monochrome digital camera using a series of color filters. Informatics tools have been developed to allow the 1931 CIE color coordinates and the relative quantum efficiencies of the materials library to be rapidly assessed and mapped against composition, crystal structure and phase purity. The range of compositions gave values of CIE _x between 0.17 and 0.52 and CIE _y between 0.48 and 0.69 with relative efficiencies in the range 2.0 × 10^-4-7.6 × 10^-4. Good agreement was obtained between the thin film phosphors and the fluorescence characteristics of a number of corresponding bulk phosphor powders. The thermal quenching of fluorescence in the thin film libraries was also measured in the temperature range 25-130 °C: The phase purity of the thin film was found to significantly influence both the relative quantum efficiency and the thermal quenching of the fluorescence.

Laser induced white emission generated by infrared excitation from Eu3+:Sr2CeO4 nanocrystals

The laser induced white emission (LIWE) was observed from Eu³⁺:Sr₂CeO₄ nanocrystals. The samples were obtained in form of powders by the modified sol-gel route. The structure and morphology of the phosphors were investigated by powder X-ray diffraction and transmission electron microscope techniques. The intense LIWE occurred under reduced pressure and focused beam of near infrared laser excitation. The power and pressure dependencies exhibit evident threshold character typical for the avalanche effect. The photoconductivity of the Eu³⁺:Sr₂CeO₄ nanocrystals measured as a function of different powers of excitation source was analyzed.

Solid state speciation of uranium and its local structure in Sr2CeO4 using photoluminescence spectroscopy

An effort was taken to carry our speciation study of uranium ion in technologically important cerate host Sr₂CeO₄ using time resolved photoluminescence spectroscopy. Such studies are not relevant only to nuclear industry but can give rich insight into fundamentals of 5f electron chemistry in solid state systems. In this work both undoped and varied amount of uranium doped Sr₂CeO₄ compound is synthesized using complex polymerization method and is characterized systematically using X-ray diffraction (XRD), Raman spectroscopy, impedance spectroscopy and scanning electron microscopy (SEM). Both XRD and Raman spectroscopy confirmed the formation of pure Sr₂CeO₄ which has tendency to decompose peritectically to SrCeO₃ and SrO at higher temperature. Uranium doping is confirmed by XRD. Uranium exhibits a rich chemistry owing to its variable oxidation state from +3 to +6. Each of them exhibits distinct luminescence properties either due to f-f transitions or ligand to metal charge transfer (LMCT). We have taken Sr₂CeO₄ as a model host lattice to understand the photophysical characteristics of uranium ion in it. Emission spectroscopy revealed the stabilization of uranium as U (VI) in the form of UO₆^6- (octahedral uranate) in Sr₂CeO₄. Emission kinetics study reflects that uranate ions are not homogeneously distributed in Sr₂CeO₄ and it has two different environments due to its stabilization at both Sr²⁺ as well as Ce⁴⁺ site. The lifetime population analysis interestingly pinpointed that majority of uranate ion resided at Ce⁴⁺ site. The critical energy-transfer distance between the uranate ion was determined based on which the concentration quenching mechanism was attributed to electric multipolar interaction. These studies are very important in designing Sr₂CeO₄ based optoelectronic material as well exploring it for actinides studies.

Down-Conversion Nitride Materials for Solid State Lighting: Recent Advances and Perspectives

Advances in solid state white lighting technologies witness the explosive development of phosphor materials (down-conversion luminescent materials). A large amount of evidence has demonstrated the revolutionary role of the emerging nitride phosphors in producing superior white light-emitting diodes for lighting and display applications. The structural and compositional versatility together with the unique local coordination environments enable nitride materials to have compelling luminescent properties such as abundant emission colors, controllable photoluminescence spectra, high conversion efficiency, and small thermal quenching/degradation. Here, we summarize the state-of-art progress on this novel family of luminescent materials and discuss the topics of materials discovery, crystal chemistry, structure-related luminescence, temperature-dependent luminescence, and spectral tailoring. We also overview different types of nitride phosphors and their applications in solid state lighting, including general illumination, backlighting, and laser-driven lighting. Finally, the challenges and outlooks in this type of promising down-conversion materials are highlighted.

Validity of Valence Estimation of Dopants in Glasses using XANES Analysis

X-ray absorption near edge structure (XANES) measurement is one of the most powerful tools for the evaluation of a cation valence state. XANES measurement is sometimes the only available technique for the evaluation of the valence state of a dopant cation, which often occurs in phosphor materials. The validity of the core excitation process should be examined as a basis for understanding the applicability of this technique. Here, we demonstrate the validity of valence estimation of tin in oxide glasses, using Sn K-edge and L-edge XANES spectra, and compare the results with ¹¹⁹Sn Mössbauer analysis. The results of Sn K-edge XANES spectra analysis reveal that this approach cannot evaluate the actual valence state. On the contrary, in L_II-edge absorption whose transition is 2p_1/2-d, the change of the white line corresponds to the change of the valence state of tin, which is calculated from the ¹¹⁹Sn Mössbauer spectra. Among several analytical approaches, valence evaluation using the peak area, such as the absorption edge energy E₀ at the fractions of the edge step or E₀ at the zero of the second derivative, is better. The observed findings suggest that the valence state of a heavy element in amorphous materials should be discussed using several different definitions with error bars, even though L-edge XANES analyses are used.

Sr1.7Zn0.3CeO4F0.2:Eu3+: novel dual-emission temperature sensors for remote, noncontact thermometric application

A novel dual-emitting temperature sensor Sr_1.7Zn_0.3CeO₄F_0.2:Eu³⁺ was synthesized. The intensity ratio shows superior linearity as a function of the temperature, indicating the potential application in the thermometry field.

Overview of the crystal chemistry of the actinide chalcogenides: incorporation of the alkaline-earth elements

This review focuses on the results of exploratory syntheses of alkaline-earth-metal actinide chalcogenides Ak–An–Q (Ak = Ba, Sr; An = Th, U; Q = S, Se, and Te). About thirty new compounds and eleven new structure types are described.

Positional flexibility: syntheses and characterization of six uranium chalcogenides related to the 2H hexagonal perovskite family

Six new uranium chalcogenides, Ba4USe6, Ba3FeUSe6, Ba3MnUSe6, Ba3MnUS6, Ba3.3Rb0.7US6, and Ba3.2K0.8US6, related to the 2H hexagonal perovskite family have been synthesized by solid-state methods at 1173 K. These isostructural compounds crystallize in the K4CdCl6 structure type in space group D3d6–R3̅c of the trigonal system with six formula units per cell. This structure type is remarkably flexible. The structures of Ba3FeUSe6, Ba3MnUSe6, and Ba3MnUS6 consist of infinite ∞1[MUQ66–] chains (M = Fe or Mn; Q = S or Se) oriented along the c axis that are separated by Ba atoms. These chains are composed of alternating M-centered octahedra and U-centered trigonal prisms sharing triangular faces; in contrast, in the structures of Ba4USe6, Ba3.3Rb0.7US6, and Ba3.2K0.8US6, there are U-centered octahedra alternating with Ba-, Rb-, or K-centered trigonal prisms. Moreover, the Ba4USe6, Ba3FeUSe6, Ba3MnUSe6, and Ba3MnUS6 compounds contain U4+, whereas Ba3.3Rb0.7US6 and Ba3.2K0.8US6 are mixed U4+/5+ compounds. Resistivity and μ-Raman spectroscopic measurements and DFT calculations provide additional insight into these interesting subtle structural variations.

Time-resolved luminescent biosensing based on inorganic lanthanide-doped nanoprobes

In this feature article, we review the latest advancements in lanthanide-doped luminescent nanocrystals as time-resolved luminescent nano-bioprobes, from their fundamental optical properties to their potential applications for ultrasensitive biodetection and high-resolution bioimaging.

Sr(1.7)Zn(0.3)CeO4: Eu3+ novel red-emitting phosphors: synthesis and photoluminescence properties

A series of novel red-emitting Sr1.7Zn0.3CeO4:Eu(3+) phosphors were synthesized through conventional solid-state reactions. The powder X-ray diffraction patterns and Rietveld refinement verified the similar phase of Sr1.7Zn0.3CeO4:Eu(3+) to that of Sr2CeO4. The photoluminescence spectrum exhibits that peak located at 614 nm ((5)D0-(7)F2) dominates the emission of Sr1.7Zn0.3CeO4:Eu(3+) phosphors. Because there are two regions in the excitation spectrum originating from the overlap of the Ce(4+)-O(2-) and Eu(3+)-O(2-) charge-transfer state band from 200 to 440 nm, and from the intra-4f transitions at 395 and 467 nm, the Sr1.7Zn0.3CeO4:Eu(3+) phosphors can be well excited by the near-UV light. The investigation of the concentration quenching behavior, luminescence decay curves, and lifetime implies that the dominant mechanism type leading to concentration quenching is the energy transfer among the nearest neighbor or next nearest neighbor activators. The discussion about the dependence of photoluminescence spectra on temperature shows the better thermal quenching properties of Sr1.7Zn0.3CeO4:0.3Eu(3+) than that of Sr2CeO4:Eu(3+). The experimental data indicates that Sr1.7Zn0.3CeO4:Eu(3+) phosphors have the potential as red phosphors for white light-emitting diodes.

Enhancing multiphoton upconversion through energy clustering at sublattice level

The applications of lanthanide-doped upconversion nanocrystals in biological imaging, photonics, photovoltaics and therapeutics have fuelled a growing demand for rational control over the emission profiles of the nanocrystals. A common strategy for tuning upconversion luminescence is to control the doping concentration of lanthanide ions. However, the phenomenon of concentration quenching of the excited state at high doping levels poses a significant constraint. Thus, the lanthanide ions have to be stringently kept at relatively low concentrations to minimize luminescence quenching. Here we describe a new class of upconversion nanocrystals adopting an orthorhombic crystallographic structure in which the lanthanide ions are distributed in arrays of tetrad clusters. Importantly, this unique arrangement enables the preservation of excitation energy within the sublattice domain and effectively minimizes the migration of excitation energy to defects, even in stoichiometric compounds with a high Yb(3+) content (calculated as 98 mol%). This allows us to generate an unusual four-photon-promoted violet upconversion emission from Er(3+) with an intensity that is more than eight times higher than previously reported. Our results highlight that the approach to enhancing upconversion through energy clustering at the sublattice level may provide new opportunities for light-triggered biological reactions and photodynamic therapy.

Synthesis and photoluminescence properties of a novel Sr2CeO4:Dy3+ nanophosphor with enhanced brightness by Li+ co-doping

A series of Dy³⁺ (0.005–0.09 mol%) and Li⁺ (0.005–0.03 mol%) co-doped strontium cerate (Sr₂CeO₄) nanopowders are synthesized by low temperature solution combustion synthesis.

Novel organic–inorganic hybrid soft xerogels with lanthanide complexes through an ionic liquid linkage

Functional hybrid soft materials [Ln(L)₄]⁻IM⁺–Al/Ti are prepared by sol–gel derived hosts based on Ti–O or Al–O groups, with an exchange reaction of the ionic liquid 3-(5-carboxy-propyl)-1-methyl-imidazolium bromide and lanthanide complexes.

Optimization of the single-phased white phosphor of Li2SrSiO4: Eu2+, Ce3+ for light-emitting diodes by using the combinatorial approach assisted with the Taguchi method

The best performance of the phosphor Li(2)SrSiO(4): Eu(2+), Ce(3+) in terms of luminescence efficiency (LE), color rendering index (CRI) and color temperature (Tc) for light-emitting diode application was optimized with combinatorial approach. The combinatorial libraries were synthesized with solution-based method and the scale-up samples were synthesized with conventional solid-reaction method. Crystal structure was investigated by using the X-ray diffraction spectrometer. The emission spectra of each sample in combinatorial libraries were measured in situ by using a fiber optic spectrometer. Fluorescence spectrometers were used to record excitation and emission spectra of bulk samples. White light generation was tuned up by tailoring Eu(2+) and Ce(3+) concentrations in the single-phased host of Li(2)SrSiO(4) under near-ultraviolet excitation, but it exhibited low efficiency of luminescence and poor color rendering index. The effects of each level of the Eu(2+) and Ce(3+) concentrations on LE, CRI, and Tc were evaluated with the Taguchi method. The optimum levels of the interaction pairs between Eu(2+) and Ce(3+) concentration on LE, CRI, and Tc were [2, 1] (0.006 M, 0.003 M), [1, 2] (0.003 M, 0.006 M), and [3, 1] (0.009 M, 0.00 3M), respectively. The thermal stability of luminescence, the external quantum efficiency (QE), luminance, chromaticity coordinates, correlated color temperature, color purity including the composition ratio of RGB in white light, and color rendering index of the white light emission of phosphor were evaluated comprehensively from a bulk sample.

NANOBIOMATERIALS LIBRARY SYNTHESIS FOR HIGH-THROUGHPUT SCREENING USING A DRY POWDER PRINTING METHOD

High-throughput (HT) screening and combinatorial searches for the discovery, development and optimization of functional materials have been widely accepted in many new materials discovery. Dry powder HT library synthesis have advantages such as using same powder materials in lab as in production, and avoiding the use of additives and/or solvents which could be harmful for cells. The VaryDose dry powder dispensing technology was adapted in this work to dispense nanobioceramic powders in quantities as low as 0.1 mg per dispensing. Nanocalcium phosphate biomaterials, including hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP), were selected to demonstrate the library fabrication. The dispensing unit design and the effect of the dispensing parameters on dosage control and uniformity are discussed.

Combinatorial study of ceramic tape-casting slurries

Ceramic tape-casting slurries are complex systems composed of ceramic powder, solvent, and a number of organic components. Conventionally, the development of ceramic tape-casting slurries is time-consuming and of low efficiency. In this work, combinatorial approaches were applied to screen the ethanol and ethyl-acetate binary solvent based slurry for ceramic green tape-casting. The combinatorial libraries were designed considering the variation of the amount of PVB (Poly vinyl-butyral) binder, polyethylene-400, and butyl-benzyl-phthalate plasticizers, and glyceryl triacetate dispersant. A parallel magnetic stirring process was used to make the combinatorial slurry library. The properties mapping of the slurry library was obtained by investigating the sedimentation and rheological characteristics of the slurries. The slurry composition was refined by scaling up the experiments and comparing the microstructure, mechanical property, and sintering behavior of green tapes made from the selected slurries. Finally, a kind of ethanol-ethyl acetate binary solvent based slurry system suitable for making X7R dielectric ceramic green tapes was achieved.

Combinatorial and high-throughput screening of materials libraries: review of state of the art

Rational materials design based on prior knowledge is attractive because it promises to avoid time-consuming synthesis and testing of numerous materials candidates. However with the increase of complexity of materials, the scientific ability for the rational materials design becomes progressively limited. As a result of this complexity, combinatorial and high-throughput (CHT) experimentation in materials science has been recognized as a new scientific approach to generate new knowledge. This review demonstrates the broad applicability of CHT experimentation technologies in discovery and optimization of new materials. We discuss general principles of CHT materials screening, followed by the detailed discussion of high-throughput materials characterization approaches, advances in data analysis/mining, and new materials developments facilitated by CHT experimentation. We critically analyze results of materials development in the areas most impacted by the CHT approaches, such as catalysis, electronic and functional materials, polymer-based industrial coatings, sensing materials, and biomaterials.

Millimeter-long carbon nanotubes: outstanding electron-emitting sources

We are reporting the fabrication of a very efficient electron source using millimeter-long and highly crystalline carbon nanotubes. These devices start to emit electrons at fields as low as 0.17 V/μm and reach threshold emission at 0.24 V/μm. In addition, these electron sources are very stable and can achieve a peak current density of 750 mA cm(-2) at only 0.45 V/μm. In order to demonstrate intense electron beam generation, these devices were used to produce visible light by cathodoluminescence. Finally, density functional theory calculations were used to rationalize the measured electronic field emission properties in open carbon nanotubes of different lengths. The modeling establishes a clear correlation between length and field enhancement factor.

Why is chemical synthesis and property optimization easier than expected?

Identifying optimal conditions for chemical and material synthesis as well as optimizing the properties of the products is often much easier than simple reasoning would predict. The potential search space is infinite in principle and enormous in practice, yet optimal molecules, materials, and synthesis conditions for many objectives can often be found by performing a reasonable number of distinct experiments. Considering the goal of chemical synthesis or property identification as optimal control problems provides insight into this good fortune. Both of these goals may be described by a fitness function J that depends on a suitable set of variables (e.g., reactant concentrations, components of a material, processing conditions, etc.). The relationship between J and the variables specifies the fitness landscape for the target objective. Upon making simple physical assumptions, this work demonstrates that the fitness landscape for chemical optimization contains no local sub-optimal maxima that may hinder attainment of the absolute best value of J. This feature provides a basis to explain the many reported efficient optimizations of synthesis conditions and molecular or material properties. We refer to this development as OptiChem theory. The predicted characteristics of chemical fitness landscapes are assessed through a broad examination of the recent literature, which shows ample evidence of trap-free landscapes for many objectives. The fundamental and practical implications of OptiChem theory for chemistry are discussed.

Tunable white-light emission in single-phased K2Y(1-x)Eu(x)Zr(PO4)3 phosphor

The single-phased K(2)Y(1-x)Eu(x)Zr(PO(4))(3) (x=0~1) phosphors were prepared by solid-state reaction. The greenish-blue Zr(4+)-emission due to the Zr(4+)-O(2-) charge transfer transition is observed in the K(2)YZr(PO(4))(3) (x=0) phosphor under UV excitation. Together with the Zr(4+)-emission, the red emission of Eu(3+) is progressively developed by replacement of Y(3+) to Eu(3+) over the full Eu-content (x=0~1) in K(2)Y(1-x)Eu(x)Zr(PO(4))(3). The emission color varies from greenish-blue to whitish with increasing Eu(3+)-content and the white-light emission is realized in single-phased phosphor of K(2)EuZr(PO(4))(3) (x=1) by combining the Zr(4+)-emission and the Eu(3+)-emission.

Combinatorial Screening of Anode and Cathode Electrocatalysts for Direct Methanol Fuel Cells

Progress in several important electrochemical technologies, including batteries, fuel cells, sensors, and electrosynthesis, is currently materials-limited. A common feature of all electrode reactions is the imbalance (i.e., loss or generation) of ions at the electrode surface. We describe in this paper a method by which excess ions in the electrode diffusion layer can be imaged, and used to identify the best electrode materials from a combinatorial array of compositions.

Although in principle this method can be applied to many electrochemical problems, we have focused on finding better electrocatalysts for direct methanol fuel cells (DMFCs). The DMFC performs two half-cell reactions: oxidation of methanol, and reduction of oxygen. Two of the most important problems in DMFCs are the poor performance of the electrocatalysts, and the crossover of methanol from the anode to the cathode side of the cell. An ideal situation would be the simultaneous development of two new catalysts: an anode that oxidizes methanol at low overpotential, and a “methanol-tolerant” cathode that reduces oxygen without oxidizing methanol.

Based on previously developed rules for predicting the activity of ternary alloy catalysts (Ley, et al., J. Electrochem. Soc. 1997, 144, 1543), we began searching quaternary combinations of noble metals for the anode, and ruthenium selenide-type materials for the cathode reaction. The anode and cathode reactions generate and consume protons, respectively, creating a substantial pH gradient at the electrode surface. Changes in local pH are imaged by means of an appropriate fluorescent indicator: Ni-PTP for the anode and Eosin Y for the cathode. DMFC testing confirms the utility of the screening method, in that a Pt/Ru/Os/Ir quaternary catalyst was substantially superior to the best binary and ternary catalysts prepared under similar conditions.