Exploring new useful phosphors by combining experiments with machine learning.

New phosphors are consistently in demand for advances in solid-state lighting and displays. Conventional trial-and-error exploration experiments for new phosphors require considerable time. If a phosphor host suitable for the target luminescent property can be proposed using computational science, the speed of development of new phosphors will significantly increase, and unexpected/overlooked compositions could be proposed as candidates.

Inverse-Perovskite Ba BO (B = Si and Ge) as a High Performance Environmentally Benign Thermoelectric Material with Low Lattice Thermal Conductivity.

High energy-conversion efficiency (ZT) of thermoelectric materials has been achieved in heavy metal chalcogenides, but the use of toxic Pb or Te is an obstacle for wide applications of thermoelectricity. Here, high ZT is demonstrated in toxic-element free Ba BO (B = Si and Ge) with inverse-perovskite structure. The negatively charged B ion contributes to hole transport with long carrier life time, and their highly dispersive bands with multiple valley degeneracy realize both high p-type electronic conductivity and high Seebeck coefficient, resulting in high power factor (PF).

Controlling the thermoelectric properties of organo-metallic coordination polymers through backbone geometry.

Poly(nickel-benzene-1,2,4,5-tetrakis(thiolate)) (Ni-btt), an organometallic coordination polymer (OMCP) characterized by the coordination between benzene-1,2,4,5-tetrakis(thiolate) (btt) and Ni ions, has been recognized as a promising p-type thermoelectric material. In this study, we employed a constitutional isomer based on benzene-1,2,3,4-tetrakis(thiolate) (ibtt) to generate the corresponding isomeric polymer, poly(nickel-benzene-1,2,3,4-tetrakis(thiolate)) (Ni-ibtt). Comparative analysis of Ni-ibtt and Ni-btt reveals several common infrared (IR) and Raman features attributed to their similar square-planar nickel-sulfur (Ni-S) coordination.

Electronic and crystal structures ofFeAsOH(= La, Sm) studied by x-ray absorption spectroscopy, x-ray emission spectroscopy, and x-ray diffraction: II pressure dependence.

We examine electronic and crystal structures of iron-based superconductorsFeAsOH(= La, Sm) under pressure by means of x-ray absorption spectroscopy (XAS), x-ray emission spectroscopy (XES), and x-ray diffraction. In LaFeAsO the pre-edge peak on high-resolution XAS at the Fe-absorption edge gains in intensity on the application of pressure up to 5.7 GPa and it saturates in the higher pressure region.

Electronic and crystal structures ofFeAsOH(= La, Sm) studied by x-ray absorption spectroscopy, x-ray emission spectroscopy, and x-ray diffraction (part I: carrier-doping dependence).

A carrier doping by a hydrogen substitution in LaFeAsOHis known to cause two superconducting (SC) domes with the magnetic order at both end sides of the doping. In contrast, SmFeAsOHhas a similar phase diagram but shows single SC dome. Here, we investigated the electronic and crystal structures for iron oxynitrideFeAsOH(= La, Sm) with the range of= 0-0.

Ship-in-a-Bottle Synthesis of High Concentration of N Molecules in a Cage-Structured Electride.

We report the formation of neutral nitrogen molecules in the cages of [CaAlO] (C12A7) framework compensated by extra-framework anions. NH treatment of C12A7 electride (C12A7:) at 800 °C leads to the formation of N and NH species in the C12A7 cages. N and NH species in the cages are identified using the Raman spectroscopy of NH and NH-treated C12A7:.

Synthesis and Photoluminescence Properties of Rare-Earth-Activated SrAAlOH (A = Ca, Ba; = 0, 1): New Members of Aluminate Oxyhydrides.

A series of aluminate-based oxyhydrides, SrAAlOH (A = Ca, Ba; = 0, 1), has been synthesized by high-temperature reaction of oxide and hydride precursors under a H atmosphere. Their crystal structures determined via X-ray and neutron powder diffraction are isostructural with tetragonal SrAlOF (space group 4/), consisting of (SrA)H layers and isolated AlO tetrahedra. Rietveld refinement based on the diffraction patterns and bond-valence-sum analysis show that Ba preferentially occupies the 10-coordinated Sr1 sites, while Ca strongly prefers to occupy the 8-coordinated Sr2 sites.

Toward 2D Magnets in the (MnBi Te )(Bi Te ) Bulk Crystal.

2D magnets and their engineered magnetic heterostructures are intriguing materials for both fundamental physics and application prospects. On the basis of the recently discovered intrinsic magnetic topological insulators (MnBi Te )(Bi Te ) , here, a new type of magnet, in which the magnetic layers are separated by a large number of non-magnetic layers and become magnetically independent, is proposed. This magnet is named as a single-layer magnet, regarding the vanishing interlayer exchange coupling.

Low-Temperature Synthesis of Perovskite Oxynitride-Hydrides as Ammonia Synthesis Catalysts.

Mixed anionic materials such as oxyhydrides and oxynitrides have recently attracted significant attention due to their unique properties, such as fast hydride ion conduction, enhanced ferroelectrics, and catalytic activity. However, high temperature (≥800 °C) and/or complicated processes are required for the synthesis of these compounds. Here we report that a novel perovskite oxynitride-hydride, BaCeONH, can be directly synthesized by the reaction of CeO with Ba(NH) at low temperatures (300-600 °C).

Nephelauxetic effect of the hydride ligand in SrLiSiOH as a host material for rare-earth-activated phosphors.

Strontium lithium orthosilicate hydride SrLiSiOH was synthesized by the reaction of SrSiO with LiH at 700 °C in a H rich atmosphere. Rietveld refinement of the neutron powder diffraction pattern revealed that SrLiSiOH is isostructural to SrLiSiOF (space group 2/) and its channel-like structure preferentially accommodates H ions over F ions. In addition, SrLiSiOH is stable in air and its Eu-doped analog exhibits yellow photoluminescence with an emission band at 544 nm and a broad excitation band ranging from 250 to 450 nm.

Improved color uniformity in white light-emitting diodes using newly developed phosphors.

We report novel white light-emitting diode (WLED) devices that improve emission color uniformity. The WLEDs consist of a violet chip and a mixed-phosphor layer of three phosphors previously developed by us. It is found that each phosphor does not reabsorb the luminescence from the other phosphors; consequently, the emission color of the WLEDs does not get affected by the mounted quantity of phosphors and/or the variation in chip emission wavelength.

Phase transition in CaFeAsH: bridging 1111 and 122 iron-based superconductors.

Iron-based superconductors can be categorized into two types of parent compounds by considering the nature of their temperature-induced phase transitions; namely, first order transitions for 122- and 11-type compounds and second-order transitions for 1111-type compounds. This work examines the structural and magnetic transitions (ST and MT) of CaFeAsH by specific heat, X-ray diffraction, neutron diffraction, and electrical resistivity measurements. Heat capacity measurements revealed a second-order phase transition that accompanies an apparent single peak at 96 K.

A novel red-emitting KCa(PO)F:Eu phosphor with a large Stokes shift.

We report a KCaPOF:Eu phosphor with a new crystal structure. This phosphor has a large Stokes shift and converts near-ultraviolet light to red luminescence without absorption of other visible light. The mechanism was elucidated by applying a constrained density functional theory to the solved crystal structure.

Nanocomposite Phosphor Consisting of CaI:Eu Single Nanocrystals Embedded in Crystalline SiO.

High luminescence efficiency is obtained in halide- and chalcogenide-based phosphors, but they are impractical because of their poor chemical durability. Here we report a halide-based nanocomposite phosphor with excellent luminescence efficiency and sufficient durability for practical use. Our approach was to disperse luminescent single nanocrystals of CaI:Eu in a chemically stable, translucent crystalline SiO matrix.

Rattling of Oxygen Ions in a Sub-Nanometer-Sized Cage Converts Terahertz Radiation to Visible Light.

A simple and robust approach to visualization of continuous wave terahertz (CW-THz) light would open up opportunities to couple physical phenomena that occur at fundamentally different energy scales. Here we demonstrate how nanoscale cages of CaAlO crystal enable conversion of CW-THz radiation to visible light. These crystallographic cages are partially occupied with weakly bonded oxygen ions and give rise to a narrow conduction band that can be populated with localized, yet mobile electrons.

Large-moment antiferromagnetic order in overdoped high- superconductor SmFeAsO D .

In iron-based superconductors, high critical temperature () superconductivity over 50 K has only been accomplished in electron-doped FeAsO ( is heavy rare earth () element). Although FeAsO has the highest bulk (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a systematic neutron powder diffraction study of SmFeAsO D , and the discovery of a long-range antiferromagnetic ordering with ≥ 0.

The Unique Electronic Structure of Mg Si: Shaping the Conduction Bands of Semiconductors with Multicenter Bonding.

The electronic structures of the antifluorite-type compound Mg Si is described in which a sublattice of short cation-cation contacts creates a very low conduction band minimum. Since Mg Si shows n-type conductivity without intentional carrier doping, the present result indicates that the cage defined by the cations plays critical roles in carrier transport similar to those of inorganic electrides, such as 12 CaO⋅7 Al O :e and Ca N. A distinct difference in the location of conduction band minimum between Mg Si and the isostructural phase Na S is explained in terms of factors such as the differing interaction strengths of the Si/S 3s orbitals with the cation levels, with the more core-like character of the S 3s leading to a relatively low conduction band energy at the Γ point.

Pressure effect on iron-based superconductor LaFeAsOH: Peculiar response of 1111-type structure.

A systematic study of the crystal structure of a layered iron oxypnictide LaFeAsOH as a function of pressure was performed using synchrotron X-ray diffraction. This compound exhibits a unique phase diagram of two superconducting phases and two parent phases. We established that the As-Fe-As angle of the FeAs tetrahedron widens on the application of pressure due to the interspace between the layers being nearly infilled by the large La and As atoms.

Ferrimagnetic Cage Framework in CaFeSiOCl.

The positively charged cage framework of the natural mineral mayenite, which enables various species with negative charge to be stabilized, is one of the key structures to provide the new functionalities exploited in applications. Here we report the structural and magnetic properties of recently found eltyubyuite, CaFeSiOCl, which is the first compound bearing a transition metal oxide as a main constituent in the mayenite-type structure. From neutron powder diffraction measurements at T = 20 K and the low temperature Mössbauer measurement, we determined the magnetic structure of eltyubyuite to be a ferrimagnet with oppositely aligned magnetic moments of +3.

Hydride-Based Electride Material, LnH2 (Ln = La, Ce, or Y).

In view of the strong electron-donating nature of H(-) and extensive vacancy formation in metals by hydrogen insertion, a series of LnH2+x (Ln = La, Ce, or Y) compounds with fluorite-type structures were verified to be the first hydride-based electride, where itinerant electrons populating the cage are surrounded by H(-) anions. The electron transfer into the cage probably originates from Ln-cage covalent interaction. To the best of our knowledge, anion-rich electrides are extremely rare, and a key requirement for their formation is that the cage site is not occupied by lone pair electrons of the adjacent ions.

Correction: Essential role of hydride ion in ruthenium-based ammonia synthesis catalysts.

[This corrects the article DOI: 10.1039/C6SC00767H.].

Essential role of hydride ion in ruthenium-based ammonia synthesis catalysts.

The efficient reduction of atmospheric nitrogen to ammonia under low pressure and temperature conditions has been a challenge in meeting the rapidly increasing demand for fertilizers and hydrogen storage. Here, we report that CaN:e, a two-dimensional electride, combined with ruthenium nanoparticles (Ru/CaN:e) exhibits efficient and stable catalytic activity down to 200 °C. This catalytic performance is due to [CaN]·eH formed by a reversible reaction of an anionic electron with hydrogen (CaN:e + H ↔ [CaN]·eH ) during ammonia synthesis.

Hydrogen-Substituted Superconductors SmFeAsO(1-x)Hx Misidentified As Oxygen-Deficient SmFeAsO(1-x).

We investigated the preferred electron dopants at the oxygen sites of 1111-type SmFeAsO by changing the atmospheres around the precursor with the composition of Sm:Fe:As:O = 1:1:1:1 - x in high-pressure synthesis. Under H2O and H2 atmospheres, hydrogens derived from H2O or H2 molecules were introduced into the oxygen sites as a hydride ion, and SmFeAsO(1-x)Hx was obtained. However, when the H2O and H2 sources were removed from the synthetic process, nearly stoichiometric SmFeAsO was obtained and the maximum amount of oxygen vacancies introduced remained x = 0.

Superconductivity in room-temperature stable electride and high-pressure phases of alkali metals.

S-band metals such as alkali and alkaline earth metals do not undergo a superconducting transition (SCT) at ambient pressure, but their high-pressure phases do. By contrast, room-temperature stable electride [Ca(24)Al(28)O(64)](4+)⋅4e(-) (C12A7:e(-)) in which anionic electrons in the crystallographic sub-nanometer-size cages have high s-character exhibits SCT at 0.2-0.

Superconductivity at 52 K in hydrogen-substituted LaFeAsO(1-x)Hx under high pressure.

The 1111-type iron-based superconductor LnFeAsO(1-x)Fx (Ln stands for lanthanide) is the first material with a Tc above 50 K, other than cuprate superconductors. Electron doping into LaFeAsO by H, rather than F, revealed a double-dome-shaped Tc-x diagram, with a first dome (SC1, 0.05 View Article and Find Full Text PDF