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A 1D organic metal halide hybrid (C8H28N5Pb3Cl11) containing metal halide nanoribbons has been developed to exhibit efficient dual emission.

This work introduces an approach to uncoupling electrons via maximum utilization of localized aromatic units, i.e., the Clar's π-sextets. To illustrate the utility of this concept to the design of Kekulé diradicaloids, we have synthesized a tridecacyclic polyaromatic system where a gain of five Clar's sextets in the open-shell form overcomes electron pairing and leads to the emergence of a high degree of diradical character. According to unrestricted symmetry-broken UCAM-B3LYP calculations, the singlet diradical character in this core system is characterized by the

Metal halide perovskites possess many physical properties amenable to optoelectronic applications, whereas the realization of these potentials has been hampered by their environmental and electronic instabilities. The morphological and molecular low dimensional perovskites and perovskite related materials have shown much promise in enhancing the chemical stability due to their unique molecular structures. Here we report on robust and reproducible four-terminal (4T) electrical measurements in a one-dimensional (1D) organic metal halide hybrid, (R)-{\alpha}-methylbenzylammonium lead triiodide ((R-{\alpha}-MBA)PbI3) made possible by its chemical stability. The results reveal a distinct intrinsic ion migration dynamic of single exponential, which underlies the unique 4T I-V characteristics. The dynamic is directly verified by real-time measurements of the transient ionic current. Our observations are consistent with photo-activation and field-assisted ion migration. The elucidated intrinsic ion dynamics may provide the physical basis for understanding and modelling the ubiquitous hysteresis in metal halides based electronic devices and new insights into the dynamics of ion migration in metal halide perovskites and hybrids in general.

Zero-dimensional (0D) organic metal halide hybrids (OMHHs) have recently emerged as a new class of light emitting materials with exceptional color tunability. While near-unity photoluminescence quantum efficiencies (PLQEs) are routinely obtained for a large number of 0D OMHHs, it remains challenging to apply them as emitter for electrically driven light emitting diodes (LEDs), largely due to the low conductivity of wide bandgap organic cations. Here, the development of a new OMHH, triphenyl(9-phenyl-9H-carbazol-3-yl) phosphonium antimony bromide (TPPcarzSbBr

Significant differences in the photochemical and photophysical behavior of

The photophysical tuning is reported for a series of tetraphenylphosphonium (TPP) metal halide hybrids containing distinct metal halides, TPP2 MXn (MXn =SbCl5 , MnCl4 , ZnCl4 , ZnCl2 Br2 , ZnBr4 ), from efficient phosphorescence to ultralong afterglow. The afterglow properties of TPP+ cations could be suspended for the hybrids containing low band gap emissive metal halide species, such as SbCl52- and MnCl42- , but significantly enhanced for the hybrids containing wide band gap non-emissive ZnCl42- . Structural and photophysical studies reveal that the enhanced afterglow is attributed to stronger π-π stacking and intermolecular electronic coupling between TPP+ cations in TPP2 ZnCl4 than in the pristine organic ionic compound TPPCl. Moreover, the afterglow in TPP2 ZnX4 can be tuned by controlling the halide composition, with the change from Cl to Br resulting in a shorter afterglow due to the heavy atom effect.

Scintillation based X-ray detection has received great attention for its application in a wide range of areas from security to healthcare. Here, we report highly efficient X-ray scintillators with state-of-the-art performance based on an organic metal halide, ethylenebis-triphenylphosphonium manganese (II) bromide ((C38H34P2)MnBr4), which can be prepared using a facile solution growth method at room temperature to form inch sized single crystals. This zero-dimensional organic metal halide hybrid exhibits green emission peaked at 517 nm with a photoluminescence quantum efficiency of ~ 95%. Its X-ray scintillation properties are characterized with an excellent linear response to X-ray dose rate, a high light yield of ~ 80,000 photon MeV−1, and a low detection limit of 72.8 nGy s−1. X-ray imaging tests show that scintillators based on (C38H34P2)MnBr4 powders provide an excellent visualization tool for X-ray radiography, and high resolution flexible scintillators can be fabricated by blending (C38H34P2)MnBr4 powders with polydimethylsiloxane., Scintillation-based X-ray detection is promising for applications in various areas ranging from security to healthcare, and low-cost and eco-friendly scintillation materials would be beneficial. Here the authors report a facile solution growth of organic manganese halide for efficient X-ray scintillation.

Zero-dimensional (0D) organic metal halide hybrids, in which organic and metal halide ions cocrystallize to form neutral species, are a promising platform for the development of multifunctional crystalline materials. Herein we report the design, synthesis, and characterization of a ternary 0D organic metal halide hybrid, (HMTA)4 PbMn0.69 Sn0.31 Br8 , in which the organic cation N-benzylhexamethylenetetrammonium (HMTA+ , C13 H19 N4 + ) cocrystallizes with PbBr4 2- , MnBr4 2- , and SnBr4 2- . The wide band gap of the organic cation and distinct optical characteristics of the three metal bromide anions enabled the single-crystalline "host-guest" system to exhibit emissions from multiple "guest" metal halide species simultaneously. The combination of these emissions led to near-perfect white emission with a photoluminescence quantum efficiency of around 73 %. Owing to distinct excitations of the three metal halide species, warm- to cool-white emissions could be generated by controlling the excitation wavelength.

Tin halide perovskites and perovskite-related materials have emerged as promising lead-free hybrid materials for various op-toelectronic applications. While remarkable progress has been achieved in...

Scintillators are utilized for X-ray detection in many important fields ranging from homeland security to health care. Developing low-cost, high-performance scintillation materials to address the i...

Bulk assemblies of zero-dimensional (0D) metal halides with exceptional structural versatility have enabled the development of a number of highly efficient emitters with tunable photophysical prope...

This work introduces an approach to uncoupling electrons via maximum utilization of localized aromatic units, i.e., the Clar’s sextets. To illustrate the utility of this concept to the design of Kekulé diradicaloids, we have synthesized a tridecacyclic polyaromatic system where a gain of five Clar’s sextets in the open shell form overcomes electron pairing and leads to the emergence of high degree of diradical character. According to unrestricted symmetry-broken UCAM-B3LYP DFT calculations, the singlet diradical character in this core system is characterized by the y0 value of 0.98 (y0 = 0 for closed shell molecule, y0 = 1 for pure diradical). The efficiency of the new design strategy was evaluated by comparing the Kekulé system with an isomeric non-Kekulé diradical of identical size, i.e., a system where the radical centers cannot couple via resonance and the high-spin ground state is unavoidable. The calculated singlet-triplet gap, i.e., the 〖ΔE〗_ST values, in both of these systems approach zero: -0.3 kcal/mol for the Kekulé and +0.2 kcal/mol for the non-Kekulé diradicaloids. The target isomeric Kekulé and non-Kekulé systems were assembled using a sequence of radical peri-annulations, cross-coupling and C-H activation. The diradicals are kinetically stabilized by six tert-butyl substituents and (triisopropylsilyl)acetylene groups. The Kekulé diradicaloid (K) has a half-life of 42 h under ambient conditions (i.e., exposure to air at the room temperature) while the non-Kekulé diradicaloid (NK) has a half-life of 2h. Both molecules are NMR-inactive but EPR-active at room temperature. The magnetic properties of the Kekulé diradicaloid was studied by superconducting quantum interference device (SQUID) to provide the experimental singlet-triplet energy gap, 〖ΔE〗_ST (K) = -0.8 kcal/mol, which was close to calculated value. Cyclic voltammetry revealed quasi-reversible two-electron oxidation and reduction processes, consistent with the presence of two degenerate partially occupied molecular orbitals.

A berkelium mellitate is added to a small family of structurally characterized Bk compounds. The 5f → 5f transitions on average blue shift and the compound changes colour with applied pressure unlike other actinide mellitates.

Ionically bonded organic metal halide hybrids have emerged as versatile multicomponent material systems exhibiting unique and useful properties. The unlimited combinations of organic cations and metal halides lead to the tremendous structural diversity of this class of materials, which could unlock many undiscovered properties of both organic cations and metal halides. Here we report the synthesis and characterization of a series benzoquinolinium (BZQ) metal halides with a general formula (BZQ)Pb2X5 (X = Cl, Br), in which metal halides form a unique two-dimensional (2D) structure. These BZQ metal halides are found to exhibit enhanced photoluminescence and stability as compared to the pristine BZQ halides, due to the scaffolding effects of 2D metal halides. Optical characterizations and theoretical calculations reveal that BZQ+ cations are responsible for the emissions in these hybrid materials. Changing the halide from Cl to Br introduces heavy atom effects, resulting in yellow room temperature phosphorescence (RTP) from BZQ+ cations.

Zero-dimensional (0D) organic metal halide hybrids are an emerging class of light emitting materials with exceptional photoluminescence quantum efficiencies (PLQEs), thanks to their perfect “host–g...

Perfluorocarboxylic acids (PFCAs) are one of the most widely detected classes of PFAS in the global environment after decades of intensive use. This study investigated the impact of perfluorinated carbon chain length on the transport behavior of PFCAs by testing and modeling two short-chain (PFPeA and PFHxA) and two long-chain PFCAs (PFOA and PFDA) in laboratory water-saturated columns. Moreover, their transport behavior was examined under different solution chemistry conditions, including pH, ionic strength, and cationic type. The experimental and simulation results indicated that the chain length had a limited impact on transport behaviors of PFPeA, PFHxA, and PFOA under various pH and ionic strengths, evidenced by their tracer-like breakthrough curves. In contrast, the mobility of PFDA was significantly affected by pH and ionic strengths. Additionally, the transport of all four PFCAs was inhabited in the presence of the divalent cation Ca

Binuclear platinum(II) complexes with strong Pt-Pt interactions are an interesting class of luminescent materials, of which photophysical properties could be controlled via multiple ways through organic ligands and Pt-Pt distance. While a number of binuclear platinum(II) complexes have been developed with tunable emissions, achieving high photoluminescence quantum efficiency (PLQE) remains challenging and of great interest. Here we report the synthesis and characterization of a series of binuclear 2,4-difluorophenylpyridine platinum(II) complexes bridged by thiazol-2-thiolate ligands with different bulkiness. The three complexes were found to have short Pt-Pt distances ranging from 2.916 to 2.945 Å. The strong Pt-Pt interactions lead to pronounced metal-metal-to-ligand charge transfer (MMLCT) absorptions between 450 and 500 nm, and strong

3-Point annulations, or phenalenannulations, transform a benzene ring directly into a substituted pyrene by "wrapping" two new cycles around the perimeter of the central ring at three consecutive carbon atoms. This efficient, modular, and general method for π-extension opens access to non-symmetric pyrenes and their expanded analogues. Potentially, this approach can convert any aromatic ring bearing a -CH2 Br or a -CHO group into a pyrene moiety. Depending upon the workup choices, the process can be directed towards either tin- or iodo-substituted product formation, giving complementary choices for further various cross-coupling reactions. The two-directional bis-double annulation adds two new polyaromatic extensions with a total of six new aromatic rings at a central core.

The two metal-deficient series of quaternary Ge-containing sulfides RE3M0.5GeS7 (RE = La–Nd, Sm; M = Co, Ni), as well as the related Si-containing sulfide Y3Pd0.5SiS7, were prepared by reactions of the elements at 1050 °C. Single-crystal X-ray diffraction analysis performed on all compounds confirmed noncentrosymmetric hexagonal structures (space group P63, Z =2) with cell parameters in the ranges of a =10.0–10.3 A and c =5.7–5.8 A for RE3Co0.5GeS7 and RE3Ni0.5GeS7, or a =9.7891(3) A and c =5.6840(4) A for Y3Pd0.5SiS7. They are classified as La3Mn0.5SiS7-type structures, with M atoms centred within octahedra (in contrast to La3CuSiS7-type structures in which M atoms occupy trigonal planar sites) and Ge atoms centred within tetrahedra, both types of polyhedra being arranged in one-dimensional stacks aligned along the c-direction. Charge balance requirements dictate half-occupancy of the M sites. However, bond valence sum arguments indicated that the M atoms are somewhat underbonded within these octahedral sites, so that there is evidence that in some compounds, they can also enter the trigonal planar site at low occupancy (~5%). Magnetic measurements on RE3Co0.5GeS7 (RE = Ce, Pr, Sm) revealed paramagnetic behaviour for the Ce and Pr members and apparent antiferromagnetic ordering (TN =14 K) for the Sm member; fitting to the Curie-Weiss law gave effective magnetic moments consistent with the presence of RE3+ and Co2+ species. Band structure calculations on ordered models of La3M0.5GeS7 (M = Co, Ni) showed that the Fermi level cuts through M 3d states in the DOS curve and supported the presence of strong M–S and Ge–S bonding interactions.

A metal-organic cage (termed FJI-C9) based on six square-shaped Cu 2 (CO 2 ) 4 paddle-wheel building units and eight flexible 1,3,5-trimethyl-2,4,6-tris(3-phenoxymethyl)benzoic acid (TTBA) linkers has been constructed. The porous FJI-C9 containing large cage of 1.5 nm shows high CO 2 adsorption uptake.

The rich chemistry of metal halide perovskites has enabled various methods of band structure control and surface passivation. Here we report a highly facile and efficient post-treatment approach for precise color tuning of cesium lead halide perovskite nanocrystals (NCs) with enhanced stability. By utilizing a special multifunctional organic ligand, triphenyl(9-phenyl-9H-carbazol-3-yl)phosphonium bromide (TPP-Carz), carbon-halide bond cleavage can be achieved to release halide ions from halogenated solvents in a controlled manner for color tuning of perovskite NCs via ion exchange. Besides controlled release of halide ions for anion exchange, TPP-Carz can effectively passivate the surfaces of perovskite NCs simultaneously. As a result, perovskite NCs prepared by this post-treatment method with tunable colors over the entire visible spectrum have shown significantly improved luminescence and stability in comparison to the ones prepared using reactive anion precursors without surface passivation by TPP-Carz.

A hollow nanostructure enables color tuning of metal halide perovskites with efficient blue emissions from cesium lead bromide., Metal halide perovskite nanocrystals (NCs) have emerged as new-generation light-emitting materials with narrow emissions and high photoluminescence quantum efficiencies (PLQEs). Various types of perovskite NCs, e.g., platelets, wires, and cubes, have been discovered to exhibit tunable emissions across the whole visible spectrum. Despite remarkable advances in the field of perovskite NCs, many nanostructures in inorganic NCs have not yet been realized in metal halide perovskites, and producing highly efficient blue-emitting perovskite NCs remains challenging and of great interest. Here, we report the discovery of highly efficient blue-emitting cesium lead bromide (CsPbBr3) perovskite hollow NCs. By facile solution processing of CsPbBr3 precursor solution containing ethylenediammonium bromide and sodium bromide, in situ formation of hollow CsPbBr3 NCs with controlled particle and pore sizes is realized. Synthetic control of hollow nanostructures with quantum confinement effect results in color tuning of CsPbBr3 NCs from green to blue, with high PLQEs of up to 81%.

The selenide Ba4Ga4GeSe12, synthesized by reaction of BaSe, Ga2Se3, and GeSe2 at 1173 K, adopts a noncentrosymmetric tetragonal structure (space group P 4 ¯ 2 1 c , Z=2, a=13.5468(4) A, c=6.4915(2) A) consisting of a three-dimensional network built from two types of corner-sharing MSe4 tetrahedra, with Ba cations occupying the intervening voids. It is isostructural to Pb4Ga4GeS12, Pb4Ga4GeSe12, and Ba4Ga4SnSe12, but differs subtly in site ordering. Structural refinements and bond valence sum analysis suggest partial disorder manifested by mixing of 0.75 Ga and 0.25 Ge within one tetrahedral site, and occupation of exclusively Ga within the other tetrahedral site. The optical band gap of 2.18(2) eV, measured from the UV/VIS/NIR diffuse reflectance spectrum, agrees with a calculated gap of 2.35 eV between valence and conduction bands and is consistent with the orange-yellow color of the crystals. Nonlinear optical measurements on powder samples revealed a weak second harmonic generation signal using 2.09 µm as the fundamental laser wavelength.

The ternary selenide Ba4Ga2Se8 has been synthesized by reaction of BaSe, Ga2Se3, and Se at 1023 K. Single-crystal X-ray diffraction analysis revealed a monoclinic structure (space group P21/c, Z=4, a=13.2393(5) A, b=6.4305(2) A, c=20.6432(8) A, β=104.3148(6)°) featuring one-dimensional chains of corner-sharing Ga-centered tetrahedra and discrete S e 2 2 − anionic units, with charge-compensating Ba2+ cations located between them. The UV/vis/NIR diffuse reflectance spectrum reveals an optical band gap of 1.63(2) eV, which is consistent with the black color of the crystals and agrees with a calculated gap of 1.51 eV obtained from band structure calculations. The presence of the S e 2 2 − units narrows the band gap in Ba4Ga2Se8 relative to other Ba–Ga–Se phases.

The electrical passivation mechanism of benzoquinone-methanol solutions on silicon has been examined through the study of the silicon surface electronic structure. Surface photovoltage (SPV) measurements using both X-ray photoelectron spectroscopy (XPS) and scanning Kelvin probe microscopy (SKPM) indicate a downward band bending of H-Si and benzoquinone (BQ) and methanol (ME) treated samples. This suggests the creation of an accumulation layer of majority carriers near the surface, with a significant field-effect contribution to the observed surface passivation. The highest SPV values recorded for the ME-Si and BQ-Si samples of about −220 mV are approaching the Fermi level—conduction band crossover. Density functional theory (DFT) calculations show that a dipole is formed upon bonding of BQ radicals on the surface, decreasing the surface electron affinity and work function. Considering the 0.07 eV shift due to the dipole and the 0.17 eV downward band bending, the work function of BQ-Si is found to be 4.08 eV. Both the dipole and downward band bending contribute to the formation of surface electron accumulation, and decrease the minority carrier density of n-Si passivated by BQ.

Semiconductor surfaces are inherently unstable, both chemically and electrically. The dangling bonds formed on cleavage lead to chemical reactivity. These same dangling bonds also act as electrical defects, and may hold charge or act as recombination centers for excited minority carriers. In this article, the difference between chemical and electrical passivation of semiconductor surfaces is discussed. Chemical passivation is provided by stoichiometric reaction with the chemical bonds. Electrical passivation may simply result from chemical reaction of the dangling bonds, or, often is provided by the presence of interfacial charge, which Coulombically repels minority carriers, thereby limiting recombination. Both organic and inorganic methods of passivating semiconductor surfaces are discussed.

The quaternary rare-earth chalcogenides RE 3 CuGaS 7 and RE 3 CuGaSe 7 ( RE =La–Nd) have been prepared by reactions of the elements at 1050 °C and 900 °C, respectively. They crystallize in the noncentrosymmetric La 3 CuSiS 7 -type structure (hexagonal, space group P 6 3 , Z =2) in which the a -parameter is largely controlled by the RE component ( a =10.0–10.3 A for the sulfides and 10.3–10.6 A for the selenides) whereas the c -parameter is essentially fixed by the choice of Ga and chalcogen atoms within tetrahedral units ( c =6.1 A for the sulfides and 6.4 A for the selenides). They extend the series RE 3 M Ga Ch 7 , previously known for divalent metal atoms ( M =Mn–Ni), differing in that the Cu atoms in RE 3 CuGa Ch 7 occupy trigonal planar sites instead of octahedral sites. Among quaternary chalcogenides RE 3 MM ′ Ch 7 , the combination of monovalent ( M =Cu) and trivalent ( M ′=Ga) metals is unusual because it appears to violate the condition of charge balance satisfied by most La 3 CuSiS 7 -type compounds. The possibility of divalent Cu atoms was ruled out by bond valence sum analysis, magnetic measurements, and X-ray photoelectron spectroscopy. The electron deficiency in RE 3 CuGa Ch 7 is accommodated through S-based holes at the top of the valence band, as shown by band structure calculations on La 3 CuGaS 7 . An optical band gap of about 2.0 eV was found for La 3 CuGaSe 7 .

Ternary rare-earth manganese arsenides RE 4 Mn 2 As 5 ( RE = La–Pr) have been synthesized by direct reactions of the elements in the presence of Ga flux. They are the first examples of RE –Mn–As phases containing trivalent RE metals. Powder and single-crystal X-ray diffraction analysis revealed that they adopt the trigonal Ce 4 Zn 2− x P 5 -type structure (space group P 3 ¯ m 1, Z = 1), with cell parameters of a = 4.2–4.3 A and c = 17.4–17.8 A. The structure consists of four-layer-thick rocksalt-type slabs [ RE As] built of RE As 6 octahedra intergrown with [Mn 2 As 2 ] slabs built of MnAs 4 tetrahedra. In contrast to the analogous Zn-containing phases, a fully stoichiometric formula RE 4 Mn 2 As 5 can be attained with no Mn deficiencies because there is no pseudogap in the density of states at the Fermi level.

A homologous series of ternary rare-earth zinc arsenides, prepared by reactions of the elements at 750 °C, has been identified with the formula RE(2-y)Zn4As4·n(REAs) (n = 2, 3, 4) for various RE members. They adopt trigonal structures: RE(4-y)Zn4As6 (RE = La-Nd), space group R3m1, Z = 3; RE(5-y)Zn4As7 (RE = Pr, Nd, Sm, Gd), space group P3m1, Z = 1; RE(6-y)Zn4As8 (RE = La-Nd, Sm, Gd), space group R3m1, Z = 3. The Zn atoms can be partially substituted by Mn atoms, resulting in quaternary derivatives RE(2-y)Mn(x)Zn(4-x)As4·n(REAs). Single-crystal structures were determined for nine ternary and quaternary arsenides RE(2-y)M4As4·n(REAs) (M = Mn, Zn) as representative examples of these series. The structures are built by stacking close-packed nets of As atoms, sometimes in very long sequences, with RE atoms occupying octahedral sites and M atoms occupying tetrahedral sites, resulting in an intergrowth of [REAs] and [M2As2] slabs. The recurring feature of all members of the homologous series is a sandwich of [M2As2]-[REAs]-[M2As2] slabs, while rocksalt-type blocks of [REAs] increase in thickness between these sandwiches with higher n. Similar to the previously known related homologous series REM(2-x)As2·n(REAs) which is deficient in M, this new series RE(2-y)M4As4·n(REAs) exhibits deficiencies in RE to reduce the electron excess that would be present in the fully stoichiometric formulas. Enthalpic and entropic factors are considered to account for the differences in site deficiencies in these two homologous series. Band structure calculations indicate that the semiconducting behaviour of the parent n = 0 member (with CaAl2Si2-type structure) gradually evolves, through a narrowing of the gap between valence and conduction bands, to semimetallic behaviour as the number of [REAs] blocks increases, to the limit of n = ∞ for rocksalt-type REAs.

International audience; The crystal structure of single crystalline members of the solid solution series Tl(V1-xCrx)5Se8 (x = 0-1 and Δx = 0.2) was determined and the magnetic and thermoelectric properties of bulk TlV5Se8 were investigated. All compounds crystallize in the pseudo-hollandite-type structure (C2/m) with a nonlinear increase in the unit cell volume due to a simultaneous increase/decrease in the transition metal distances across the edge/face-sharing octahedra. A slight Tl deficiency was found for single crystalline TlV5Se8 and Tl(V0.8Cr0.2)5Se8 as well as for bulk TlV5Se8 according to Rietveld and single crystal structure refinements. The metallic character of bulk TlV5Se8 and its low electrical resistivity compared to poly- and single-crystalline TlCr5Se8 can probably be associated with this probable Tl deficiency. In TlV5Se8, anomalies in the low temperature Seebeck coefficient, i.e. a maximum at T ∼ 14 K and two sign changes at T ∼ 47 K and T ∼ 167 K, were found. Bulk TlV5Se8 is a highly frustrated (f = /TN ≈ 42 K) Curie-Weiss paramagnet ordering antiferromagnetically ( = -1287 K) below TN ≈ 31 K with an effective magnetic moment of μ = 2.68 μB corresponding to V3+. Low-field M(H) measurements revealed the existence of a small ferromagnetic component below TN in bulk TlV5Se8 and, despite the observed spin frustration, no spin glass phase was found in this compound. © 2015 The Royal Society of Chemistry.

The nonlinear optical (NLO) BaGa 4 S 7 polycrystalline materials with stoichiometric composition were synthesized from BaS, Ga, and S via solid-state reactions in the dual temperature zone rocking furnace with excess sulfur, and crystal BaGa 4 S 7 for the mid-infrared (IR) was grown with Bridgman–Stockbarger technique. The ultraviolet (UV) and IR optical absorption edges of crystal BaGa 4 S 7 were found to be at 350 nm and 13.7 μm, respectively. Its thermal conductivities at 50 °C were 1.45 W/(m K), 1.58 W/(m K) and 1.68 W/(m K) along a -, b - and c -directions, respectively. The laser damage threshold of a single crystal was about 7.1 J/cm 2 at 2.1 μm, and 26.2 J/cm 2 at 9.58 μm. The idler non-critical phase-matching OPO wavelength was between 6 and 10 μm when the pumped wavelength was varied around 2.2 μm.

Two series of Mn-substituted rare-earth zinc arsenides RE(1-y)Mn(x)Zn(2-x)As2 (RE = Eu-Lu) and RE(2-y)Mn(x)Zn(4-x)As4 (RE = La-Nd, Sm, Gd) were prepared by reaction of the elements at 750 °C. Both series are derived from ideal empirical formula REM2As2 (M = Mn, Zn) and adopt crystal structures related to the trigonal CaAl2Si2-type (space group P3m1) in which hexagonal nets of RE atoms and [M2As2] slabs built up of edge-sharing M-centered tetrahedra are alternately stacked along the c-direction. For compounds with divalent RE components (Eu, Yb), the fully stoichiometric and charge-balanced formula REM2As2 is obtained, with Mn and Zn atoms statistically disordered within the same tetrahedral site. For compounds with trivalent RE components, the RE sites become deficient, and the Mn atoms are segregated from the Zn atoms in separate tetrahedral sites. Within the series RE(1-y)Mn(x)Zn(2-x)As2 (Gd-Tm, Lu), the parent CaAl2Si2-type structure is retained, and the Mn atoms are disordered within partially occupied interstitial sites above and below [Zn(2-x)As2] slabs. Within the series RE(2-y)Mn(x)Zn(4-x)As4 (RE = La-Nd, Sm, Gd), the c-axis becomes doubled as a result of partial ordering of Mn atoms between every other pair of [Zn(2-x)As2] slabs. Attempts to synthesize Gd-containing solid solutions with the charge-balanced formula Gd0.67Mn(x)Zn(2-x)As2 suggested that these phases could be formed with up to 50% Mn substitution. Band structure calculations reveal that a hypothetical superstructure model with the formula La1.33MnZn3As4 would have no gap at the Fermi level and that slightly lowering the electron count alleviates antibonding Mn-As interactions; a spin-polarized calculation predicts nearly ferromagnetic half-metallic behavior. X-ray photoelectron spectroscopy confirms the presence of divalent Mn in these compounds.

Four series of ternary rare-earth zinc arsenides have been prepared by reaction of the elements at 750 °C: RE4Zn(2-x)As5 forming for RE = La-Nd, Sm; and RE5Zn(2-x)As6, RE6Zn(2-x)As7, RE7Zn(2-x)As8 forming for RE = Ce, Pr, Nd, Sm. They crystallize in trigonal structure types in space group P3m1 with Z = 1 for RE4Zn(2-x)As5 and RE7Zn(2-x)As8, or space group R3m1 with Z = 3 for RE5Zn(2-x)As6 and RE6Zn(2-x)As7. Through the structural principle of intergrowing rocksalt-type [REAs] slabs of variable thickness within a parent CaAl2Si2-type structure containing Zn-deficient [Zn(2-x)As2] slabs built from edge-sharing Zn-centered tetrahedra, these ternary arsenides belong to a homologous series with the formulation REZn(2-x)As2·n(REAs) (n = 3, 4, 5, 6). Quaternary derivatives Ce4(Mn,Zn)(2-x)As5 and Ce6(Mn,Zn)(2-x)As7 were also obtained in which Mn partially substitutes for Zn. Band structure calculations predict that the electronic properties can be gradually modified from semiconducting to semimetallic behavior as more [REAs] slabs are introduced.

The ternary rare-earth zinc arsenides RE Zn 2 As 3 ( RE =La–Pr) have been prepared by reactions of the elements at 800 °C. They adopt new tetragonal structure types, with the La member (space group I 4/ mmm , Z =4, a =4.1133(2) A, c =32.1246(14) A) differing from the Ce and Pr members (space group P 4/ nmm , Z =2, a =4.0804(6)–4.0534(12) A, c =16.089(5)–16.059(10) A, respectively) in the disposition of RE -centred square antiprisms on opposite sides of square As nets. The structures contain thick anionic slabs, built from edge-sharing ZnAs 4 tetrahedra, that can be considered either as stackings of three PbO-type layers or as fragments of the fluorite-type structure. These slabs are deficient in Zn and are reminiscent of the same features in binary arsenide Zn 3 As 2 . LaZn 2 As 3 exhibits temperature-independent paramagnetism whereas CeZn 2 As 3 follows modified Curie–Weiss behavior consistent with Ce 3+ species but with no occurrence of long-range ordering.

The quaternary Ga-containing chalcogenides La3Ag0.6GaS7, La3Ag0.6GaSe7, La3ZnGaSe7, and La3CdGaSe7, as well as the related ternary chalcogenide La3Ga1.67S7, were prepared by reactions of the elements at 950 °C. They adopt noncentrosymmetric hexagonal structures (space group P63, Z=2) with cell parameters (a=10.2 A, c=6.1 A for the sulfides; a=10.6 A, c=6.4 A for the selenides) that are largely controlled by the geometrical requirements of one-dimensional stacks of Ga-centered tetrahedra separated by the La atoms. Among these compounds, which share the common formulation La3M1–xGaCh7 (M=Ga, Ag, Zn, Cd; Ch=S, Se), the M atoms occupy sites within a stacking of trigonal antiprisms formed by Ch atoms. The location of the M site varies between extremes with trigonal antiprismatic (CN6) and trigonal planar (CN3) geometry. Partial occupation of these sites and intermediate ones accounts for the considerable versatility of these structures and the occurrence of large metal displacement parameters. The site occupations can be understood in a simple way as being driven by the need to satisfy appropriate bond valence sums for both the M and Ch atoms. Band structure calculations rationalize the substoichiometry observed in the Ag-containing compounds (La3Ag0.6GaS7, La3Ag0.6GaSe7) as a response to overbonding. X-ray photoelectron spectroscopy supports the presence of monovalent Ag atoms in these compounds, which are not charge-balanced.

The selenide Ba4Ga4GeSe12, synthesized by reaction of BaSe, Ga2Se3, and GeSe2 at 1173 K, adopts a noncentrosymmetric tetragonal structure (space group P 4 ¯ 2 1 c , Z=2, a=13.5468(4) A, c=6.4915(2) A) consisting of a three-dimensional network built from two types of corner-sharing MSe4 tetrahedra, with Ba cations occupying the intervening voids. It is isostructural to Pb4Ga4GeS12, Pb4Ga4GeSe12, and Ba4Ga4SnSe12, but differs subtly in site ordering. Structural refinements and bond valence sum analysis suggest partial disorder manifested by mixing of 0.75 Ga and 0.25 Ge within one tetrahedral site, and occupation of exclusively Ga within the other tetrahedral site. The optical band gap of 2.18(2) eV, measured from the UV/VIS/NIR diffuse reflectance spectrum, agrees with a calculated gap of 2.35 eV between valence and conduction bands and is consistent with the orange-yellow color of the crystals. Nonlinear optical measurements on powder samples revealed a weak second harmonic generation signal using 2.09 µm as the fundamental laser wavelength.

Eight new quaternary chalcogenides BaRE2In2Ch7 (RE = La–Nd; Ch = S, Se) have been prepared by reactions of BaCh, In2Ch3, RE, and Ch at high temperatures. They adopt orthorhombic structures (space group Pbam, Z = 2; a = 11.6300(8)–11.5895(7) A, b = 12.4202(9)–12.3001(8) A, c = 4.0689(3)–4.0028(2) A for the sulfides; a = 12.1515(6)–12.1358(10) A, b = 12.9367(7)–12.8510(11) A, c = 4.1966(2)–4.1363(4) A for the selenides) containing one-dimensional anionic [In2Ch7] ribbons of corner-sharing InCh5 trigonal bipyramids, separated by Ba and RE cations. The structure is an ordered variant of the rare Eu3Sn2S7-type with Ba atoms occupying larger sites with nearly cubic geometry and RE atoms occupying smaller sites with bicapped trigonal prismatic geometry. The InCh5 trigonal bipyramids, which are unusual, exhibit four shorter In–Ch bonds and a fifth longer one. Band structure calculations indicate that BaLa2In2S7 is a direct gap semiconductor, and corroborate the description of the In coordination as CN4 + 1. On the basis of the optical absorption spectra, band gaps were estimated to be 1.87(2) eV for BaLa2In2S7 and 1.66(2) eV for BaLa2In2Se7.