Site Symmetry Research Articles

Multi-site incorporation of Cr3+ in CaAl12O19

In this study, a series of Cr3+-doped CaAl12O19 exhibiting multi-site luminescence was prepared by the solid-state reaction in air. Time-resolved spectroscopy revealed that luminescence spectra consist of three spectral components: narrowband emission at 689 nm, wideband emission at 785 nm and previously unreported narrowband emission at 700 nm with unusually long photoluminescence lifetime. Electron paramagnetic resonance (EPR) spectroscopy confirmed that Cr3+ forms three centres with different site symmetries. Based on the results, the assignment of Cr3+ luminescence centres, EPR signals and Al crystallographic sites in CaAl12O19 was performed, expanding the knowledge base on the relationship between optical properties of Cr3+ ions and the host structure.

Crystal structure of Cs2GdNb6Cl15O3 in the structural evolution of niobium oxychlorides with octa-hedral Nb6-cluster units.

Cs2GdNb6Cl15O3, dicaesium gadolinium hexa-niobium penta-deca-chloride trioxide, was synthesized by solid-state reactions starting from a stoichiometric mixture of CsCl, Gd2O3, Nb, NbCl5, and Nb2O5. The crystal structure is based on octa-hedral Nb6 cluster units (point group symmetry 3.2) with composition [(Nb6Cli 9Oi 3)Cla 6]5- where i and a denote inner and outer ligands. Cs2GdNb6Cl15O3 exhibits 14 valence electrons per cluster unit. The cluster units are linked to each other by CsI and GdIII atoms, whereby CsI (site symmetry 3..) is 12-coordinated by six Cli and six Cla ligands belonging to six neighboring cluster units and GdIII (site symmetry 3.2) is 9-coordinated by three Oi and six Cli ligands belonging to three adjacent cluster units. The arrangement of cluster units corresponds to a stacking of …AA'A… layers along [001]. Cs2GdNb6Cl15O3 is isotypic with Cs2UNb6Cl15O3.

Crystal structures of five halido gold complexes involving piperidine or pyrrolidine as ligands or (protonated) as cations.

In bromido-(pyrrolidine-κN)gold(I) bis-(pyrrolidine-κN)gold(I) bromide, [AuBr(pyr)]·[Au(pyr)2]Br (pyr = pyrrolidine, C4H9N), 2, alternating [AuBr(pyr)] mol-ecules and [Au(pyr)2]+ cations are connected by aurophilic contacts to form infinite chains of residues parallel to the b axis. The chains are cross-linked by three N-H⋯Br- hydrogen bonds and an Au⋯Br contact to form a layer structure parallel to the ab plane. Tri-chlorido-(piperidine-κN)gold(III), [AuCl3(pip)] (pip = piperidine, C5H11N), 3, consists of mol-ecules with the expected square-planar coordination at the gold atom, which are connected by an N-H⋯Cl hydrogen bond and an Au⋯Cl contact to form a layer structure parallel to the ac plane. The structures of bis-(piperidinium) tetra-chlorido-aurate(III) chloride, (pipH)2[AuCl4]Cl, 4, and bis-(pyrrolidinium) tetra-bromido-aurate(III) bromide, (pyrH)2[AuBr4]Br, 6, are closely related but not isotypic. Compound 6 crystallizes in space group Ibam; the Au and two Br atoms of the anion lie in the mirror plane x, y, 0, whereas the bromide ions occupy special positions 0, 0.5, 0 and 0, 0.5, 0.25, with site symmetry 2/m. The NH2 group forms a hydrogen bond to one bromide ion, and also a three-centre hydrogen bond to the other bromide atom and to a metal-bonded Br atom. The packing involves chains of hydrogen-bonded pyrrolidinium and bromide ions parallel to the c axis, combined with a layer structure of [AuBr4]- and bromide anions, parallel to the ab plane and involving Au⋯Br and Br⋯Br contacts. Compound 4, however, crystallizes pseudosymmetrically in space group Iba2; two chlorine atoms of the anion lie on the twofold axis 0.5, 0.5, z, and there are two independent cations. The packing is closely similar to that of 6, but there are no N-H⋯Cl hydrogen bonds to metal-bonded chlorines. The contact distances Au⋯Cl are appreciably longer than their Au⋯Br counterparts in 6, whereas the Cl⋯Cl contact is much shorter than Br⋯Br in 6. Tri-bromido-(piperidine-κN)gold(III) crystallizes as its di-chloro-methane solvate, [AuBr3(pip)]·CH2Cl2, 7. It too displays a square-planar coordination at the gold atom. The packing involves hydrogen bonds N-H⋯Br, stacking of neighbouring AuBr3 units by Au⋯Br contacts, and a short Br⋯Br contact; these combine to form a layer structure parallel to the ac plane.

Symmetry-Mismatched SBU Transformation in MOFs: Postsynthetic Metal Exchange from Zn to Fe and Its Effects on Gas Adsorption and Dye Selectivity.

This research explores the alteration of metal-organic frameworks (MOFs) using a method called postsynthetic metal exchange. We focus on the shift from a Zn-based MOF containing a [Zn4O(COO)6] secondary building unit (SBU) of octahedral site symmetry (ANT-1(Zn)) to a Fe-based one with a [Fe3IIIO(COO)6]+ SBU of trigonal prismatic site symmetry (ANT-1(Fe)). The symmetry-mismatched SBU transformation cleverly maintains the MOF's overall structure by adjusting the conformation of the flexible 1,3,5-benzenetribenzoate linker to alleviate the framework strain. The process triggers a decrease in the framework volume and pore size alongside a change in the framework's charge. These alterations influence the MOF's ability to adsorb gas and dye. During the transformation, core-shell MOFs (ANT-1(Zn@Fe)) are formed as intermediate products, demonstrating unique gas sorption traits and adjusted dye adsorption preferences due to the structural modifications at the core-shell interface. Heteronuclear clusters, located at the framework interfaces, enhance the heat of CO2 adsorption. Furthermore, they also influence the selectivity of the dye size. This research provides valuable insights into fabricating novel MOFs with unique properties by modifying the SBU of a MOF with flexible organic linkers from one site symmetry to another.

Synthesis and crystal structure of silicon pernitride SiN2 at 140 GPa.

Silicon pernitride, SiN2, was synthesized from the elements at 140 GPa in a laser-heated diamond anvil cell. Its crystal structure was solved and refined by means of synchrotron-based single-crystal X-ray diffraction data. The title compound crystallizes in the pyrite structure type (space group Pa , No. 205). The Si atom occupies a site with multiplicity 4 (Wyckoff letter b, site symmetry ..), while the N atom is located on a site with multiplicity 8 (Wyckoff letter c, site symmetry .3.). The crystal structure of SiN2 is comprised of slightly distorted [SiN6] octa-hedra inter-connected with each other by sharing vertices. Crystal chemical analysis of bond lengths suggests that Si has a formal oxidation state of +IV, while nitro-gen forms pernitride anions (N-N)4-.

Modulating the Reaction Configuration by Breaking the Structural Symmetry of Active Sites for Efficient Photocatalytic Reduction of Low-concentration CO2.

Photocatalytic conversion of low-concentration CO2 is considered as a promising way to simultaneously mitigate the environmental and energy issues. However, the weak CO2 adsorption and tough CO2 activation process seriously compromise the CO production, due to the chemical inertness of CO2 molecule and the formed fragile metal-C/O bond. Herein, we designed and fabricated oxygen vacancy contained Co3O4 hollow nanoparticles on ordered macroporous N-doped carbon framework (Vo-HCo3O4/OMNC) towards photoreduction of low-concentration CO2. In-situ spectra and ab initio molecular dynamics simulations reveal that the constructed oxygen vacancy is able to break the local structural symmetry of Co-O-Co sites. The formation of asymmetric active site switches the CO2 configuration from a single-site linear model to a multiple-sites bending one with a highly stable configuration, enhancing the binding and structural polarization of CO2 molecules. As a result, Vo-HCo3O4/OMNC shows unprecedent activity in the photocatalytic conversion of low-concentration CO2 (10% CO2/Ar) under laboratory light source or even natural sunlight, affording a syngas yield of 337.8 or 95.2 mmol g-1 h-1, respectively, with an apparent quantum yield up to 4.2%.

Modulating the Reaction Configuration by Breaking the Structural Symmetry of Active Sites for Efficient Photocatalytic Reduction of Low‐concentration CO2

AbstractPhotocatalytic conversion of low‐concentration CO2 is considered as a promising way to simultaneously mitigate the environmental and energy issues. However, the weak CO2 adsorption and tough CO2 activation process seriously compromise the CO production, due to the chemical inertness of CO2 molecule and the formed fragile metal‐C/O bond. Herein, we designed and fabricated oxygen vacancy contained Co3O4 hollow nanoparticles on ordered macroporous N‐doped carbon framework (Vo−HCo3O4/OMNC) towards photoreduction of low‐concentration CO2. In situ spectra and ab initio molecular dynamics simulations reveal that the constructed oxygen vacancy is able to break the local structural symmetry of Co−O−Co sites. The formation of asymmetric active site switches the CO2 configuration from a single‐site linear model to a multiple‐sites bending one with a highly stable configuration, enhancing the binding and structural polarization of CO2 molecules. As a result, Vo−HCo3O4/OMNC shows unprecedent activity in the photocatalytic conversion of low‐concentration CO2 (10 % CO2/Ar) under laboratory light source or even natural sunlight, affording a syngas yield of 337.8 or 95.2 mmol g−1 h−1, respectively, with an apparent quantum yield up to 4.2 %.

Centrohexaindane, a Unique Polyaromatic Hydrocarbon Bearing the Rare Cq (Cq )4 Core: Inelastic Neutron Scattering, Infrared and Raman Spectroscopy.

The structure and vibrational spectroscopy of centrohexaindane, 1, was investigated. This unusual molecule has a quaternary carbon atom that is coordinated to four further such quaternary carbon atoms as its core, each pair of which is bonded to an ortho-phenylene unit. Previous NMR studies have shown that the molecule has tetrahedral (Td ) symmetry in solution. The infrared and Raman spectra of chloroform and deuterochloroform solutions of 1 are completely in agreement with this conclusion, as the only modes that are visible are those allowed for Td symmetry. This is not the case in the solid state: X-ray powder diffraction indicates that the unit cell is triclinic or monoclinic with a volume in excess of 4000 Å3 . The vibrational spectroscopy is consistent with C1 site symmetry and the presence of at least two molecules in the primitive cell. It is likely that the space group is centrosymmetric.

Synthesis and crystal structure of catena-poly[cobalt(II)-di-μ-chlorido-μ-pyridazine-κ2N1:N2

The reaction of cobalt dichloride hexa-hydrate with pyridazine leads to the formation of crystals of the title compound, [CoCl2(C4H4N2)]n. This compound is isotypic to a number of compounds with other divalent metal ions. Its asymmetric unit consists of a Co2+ atom (site symmetry 2/m), a chloride ion (site symmetry m) and a pyridazine mol-ecule (all atoms with site symmetry m). The Co2+ cations are coordinated by four chloride anions and two pyridazine ligands, generating trans-CoN4Cl2 octa-hedra, and are linked into [010] chains by pairs of μ-1,1-bridging chloride anions and bridging pyridazine ligands. In the crystal structure, the pyridazine ligands of neighboring chains are stacked onto each other, indicating π-π inter-actions. Powder X-ray diffraction proves that a pure crystalline phase was obtained. Differential thermonalysis coupled to thermogravimetry (DTA-TG) reveal that decomposition is observed at about 710 K. Magnetic measurements indicate low-temperature metamagnetic behavior as already observed in a related compound.

Indistinguishable telecom band photons from a single Er ion in the solid state.

Atomic defects in the solid state are a key component of quantum repeater networks for long-distance quantum communication1. Recently, there has been significant interest in rare earth ions2-4, in particular Er3+ for its telecom band optical transition5-7 that allows long-distance transmission in optical fibres. However, the development of repeater nodes based on rare earth ions has been hampered by optical spectral diffusion, precluding indistinguishable single-photon generation. Here, we implant Er3+ into CaWO4, a material that combines a non-polar site symmetry, low decoherence from nuclear spins8 and is free of background rare earth ions, to realize significantly reduced optical spectral diffusion. For shallow implanted ions coupled to nanophotonic cavities with large Purcell factor, we observe single-scan optical linewidths of 150 kHz and long-term spectral diffusion of 63 kHz, both close to the Purcell-enhanced radiative linewidth of 21 kHz. This enables the observation of Hong-Ou-Mandel interference9 between successively emitted photons with a visibility of V = 80(4)%, measured after a 36 km delay line. We also observe spin relaxation times T1,s = 3.7 s and T2,s > 200 μs, with the latter limited by paramagnetic impurities in the crystal instead of nuclear spins. This represents a notable step towards the construction of telecom band quantum repeater networks with single Er3+ ions.

(Invited) Understanding the Role of Dopants (Al, Zn, Zr) in Altering Charge-Storage Capacity and Cycling Profiles of VFe2Ox

Vanadium ferrite (VFe2Ox) is a defective spinel system that can incorporate substantial Li+ and exhibits a high charge–discharge rate, particularly when structured as a nanoscale aerogel.1 Cations such as Zr, Zn and Al,2 can readily enter the structure substitutionally and have strong, but differing effects on the charge-storage capacity of the material. These earth abundant, cost- effective constituent elements give this class of materials strong potential as future Li-ion battery cathodes but optimizing the stoichiometry for maximum capacity and stability will require understanding the redox sequence of the host cations (Fe, V) and role of intentional dopants.We use density functional theory calculations in concert with in situ and operando X-ray absorption near-edge spectroscopy (XANES) spectra obtained using an in-lab X-ray absorption spectrometer to uncover the quantum mechanical-level effects that underpin relevant energy- storage behaviors of doped and undoped VFe2Ox. Our experimental V K-edge and Fe K-edge spectra indicate reduction of both species during discharge but cannot distinguish between tetrahedral and octahedral Fe redox sites or fully resolve the valency of each element as a function of state of charge. Using a hybrid form of density functional theory that accounts for the strong correlation present in 3d elements, we show that both V and Fe are indeed reduced, but that only tetrahedral Fe is redox active until fully converted to Fe2+. Furthermore, both octahedral and tetrahedral Fe3+ are high spin configuration, but the 5μB moments in the fully filled majority spin channel at each symmetry site are anti-aligned. This arrangement allows for easy exchange of electrons and facilitates conduction. We also calculate XANES spectra based on first principles calculations to be compared directly to those measured in the lab. This cross- check allows us to understand the effect of Al, Zr, and Zn dopants on the redox sequence and relate these results to site preference and capacity. Our combined experimental and calculational investigation sheds light on how these complex materials store Li ions and points toward future alterations that may further improve their properties.

“Structural and NIR photoluminescence studies from Nd3+-doped yttrium niobate: A potential material for photonics”

In the present work, an original sol-gel methodology is explored for the synthesis of Nd3+-doped yttrium niobate materials. The main goal was to assess the effect of the dopant concentration on the structural and luminescent properties, specifically in the near-infrared region, aiming for a future biophotonics application. X-ray diffraction and Raman spectroscopy analyses revealed the crystallization of the cubic Y3NbO7 and monoclinic YNbO4 phases, with preferential stabilization of the cubic Y3NbO7, a fluorite-like structure, irrespective of the dopant concentration. All samples presented an intense NIR emission in the second biological window (1000–1500 nm) under excitation at 808 nm (NIR–I excitation), with a prevalence for the 1064 nm emission, indicating the potential application in the biophotonics field. Up to 5 mol% Nd3+ content did not modify the spectral profiles, and the lifetime decay for the 4F3/2 emission level showed that the quenching concentration was 1.78 mol% Nd3+. Higher Nd3+ content revealed broader emission bands, attributed to higher occupation of Y3NbO7 symmetry sites. Emission at NIR-IIa biological window, at 1336 nm, attributed to the 4F3/2 → 4I13/2 was detected indicating the distribution of Nd3+ ions in a low phonon energy environment. The as-reported materials reveal potential application as solid-state lasers and bioimaging probes at NIR-IIa biological window.

Hypersensitivity and nephelauxetic effect of Er3+ in bismuth tellurite glass system

The optical absorption and emission properties of 20Li2O-xBi2O3-(78-x)TeO2-1Er2O3-1Ag glass system had been analyzed to investigate the hypersensitivity shift and its mechanism. According to the Covalent model, the hypersensitive shift indicated by the drop of F2 at x = 5 mol% can be attributed to charge transfer from O2– ligands to Er3+ ions meanwhile according to the Dielectric screening model, drop of F2 may due to Er3+ ions contraction. The dynamic coupling mechanism was used to explain hypersensitivity transition probabilities in non-centrosymmetric systems. The addition of Bi2O3 may modify the site symmetry of Er3+ ions and oxygen to a high asymmetry τ2, resulting in an asymmetrical electron distribution, thus increasing Er-O covalency, as shown by the maximum Ω2 value at x = 5 mol%. The Er3+ ions site symmetry was investigated using Hamiltonian crystal field fitting in the frame of the D4 point symmetry model, which yielded maximum crystal field strength Nv at x = 5 mol%, indicating low point symmetry distortion of the Er3+ ions site symmetry.

Crystal structure and luminescence dynamics of highly pure LiM(PO3)3:Eu3+ (M = Sr, Ca) red phosphors for white light emitting diodes

Highly pure red phosphors LiM(PO3)3:Eu3+ (M = Sr, Ca) doped with Eu3+ (1 mol%) were synthesized via solution combustion method and their crystal structure and luminescence dynamics were studied to explore its suitability in white light emitting diodes. The Rietveld refinement analysis of the powder X-ray diffraction patterns reveals that the phosphors belong to the pure triclinic phase of LiSr(PO3)3 and LiCa(PO3) with space group P-1¯ (2). The scanning electron microscopy images showed the agglomerated morphology. The photoluminescence emission spectra under 393 nm show an orange band at 594 nm and a red band at 613 nm ascribed to 5D0 → 7F1, 5D0 → 7F2 transitions of Eu3+ ion in both the phosphors. Moreover, the spectroscopic properties such as luminescence behaviour, and Stark splitting were used to examine the symmetry of Eu3+ ions in LiM(PO3)3:Eu3+ (M = Sr, Ca) phosphors in terms of distortion induced upon doping. The Stark splitting shows that the actual site symmetry for Eu3+ ion was estimated to be D2 type for both phosphors. The photometric properties of LiCa(PO3)3:Eu3+ such as Commission International de l’Eclairage coordinates (x = 0.64, y = 0.36) near to the standard one (red), high color purity (95%) and higher brightness reveal that the phosphor has the capability of acting as a red component in n-UV white light emitting diodes.

Luminescence studies of high color purity red-emitting [formula omitted] phosphor prepared by microwave-assisted synthesis technique

A set of red-emitting phosphor materials (Ca1−xAl4O7:Eux3+, x = 0, 0.01, 0.03, 0.05, 0.07, 0.09, 0.11, 0.13) were synthesized through microwave-assisted combustion synthesis for the first time. The crystal structures and phase purity of Eu3+ ions-activated calcium dialuminate (CaAl4O7) phosphor were investigated by XRD study and Rietveld refinement analysis were performed. The prepared phosphors exhibit monoclinic crystal structure having C2/c space group. From the radius difference percentage calculation, the occupancy of Eu3+ ions in Ca2+ sites was confirmed which is in better harmony with the refinement result. Morphological analysis was investigated through SEM study. Structural characteristics and the presence of the functional groups were analysed though FTIR study. The optical band gap (Eg) was determined to be 5.46 eV by studying the UV–VIS reflectance spectra. PL measurements were carried out for the prepared material to study the luminescent behaviour. The presence of charge transfer band was observed in the excitation spectra. It is found that the prepared phosphor materials exhibits emission rich in red at 611 nm with fixed excitation wavelength at 393 nm. The concentration quenching and energy transfer kinetics were analysed by employing Blasse and Dexter’s formula that attributed the non-radiative energy transfer to the dipole-dipole (d-d) interactions. Local site symmetry was analysed to study the symmetry of the environment in the neighbourhood of Eu3+ ions in the host matrix. To analyse the colorimetric performance of the phosphor materials, the correlated color temperature (CCT), color purity were calculated by using the CIE chromaticity co-ordinates (CIE 1931). The calculated CCT value shows the appearance of the emitted color of the phosphor in the warmer region. CaAl4O7:Eu3+ phosphor manifests high color purity which was found to be 97.39 %. The PL decay time measurement were performed for Ca1−xAl4O7:Eux3+ (x = 0.07) phosphor to obtain the decay lifetime. The estimated decay time (1.44 ms) indicates that the prepared phosphor material has a good potency to be utilized as a red-emitting phosphor for wLED, display technology and other applications.

Boosting STE and Nd3+ NIR Luminescence in Cs2AgInCl6 Double Perovskite via Na+/Bi3+‐Induced Local Structure Engineering

AbstractCurrently, lanthanide (Ln3+) doped Pb‐free double perovskites (DPs) suffer from competitive emissions of the self‐trapped exciton (STE) and Ln3+. Herein, a new type of Nd3+‐doped Cs2AgInCl6 DPs with Na+/Bi3+ co‐alloying is developed. Benefiting from Na+/Bi3+‐induced local structural modification, both STE broadband visible luminescence and Nd3+ near‐infrared (NIR) emissions are boosted via free exciton sensitization. Specifically, a total 648‐fold enhancement in emitting intensities compared to the Na+/Bi3+‐free counterpart is realized, with a significantly improved NIR photoluminescence quantum yield (PLQY) from 0.16% to 30.3%. First‐principles density functional theory calculations, Raman spectra, and steady/transient‐state PL spectra verify the modification of local site symmetry, breakdown of parity‐forbidden absorption, and reduction of electron‐phonon coupling via Na+/Bi3+ doping. Finally, a compact vis–NIR broadband light‐emitting diode (LED) is designed by coupling the Na/Bi/Nd: Cs2AgInCl6 DP with a commercial ultraviolet LED chip, which shows promising applications in spectroscopic analyses and multifunctional lighting.

Structural, morphological, and optical characteristics of Gd2 Si2 O7 :Dy3+ nanophosphors for WLEDs.

Yellowish-white light-emitting Gd2-x Si2 O7 :xDy3+ (x = 1-5 mol%) nanophosphors were prepared using a solution combustion synthesis method. Fluorescence spectrophotometry and X-ray diffraction measurements were performed to scrutinize the optical performances and phase recognition of the designated nanophosphors. The outcomes specified that the prepared phosphors were crystallized into a triclinic phase with a P-1 space group. As the concentration of Dy3+ ions was increased, the unit-cell volume decrease proportionally due to the replacement of large-sized Gd3+ by small-sized Dy3+ ions. Under ultraviolet excitation at 349 nm, emission spectra consisted of two pronounced emission lines at ~482 nm (blue line), ~578 nm (yellow line), and a relatively weaker emission at ~670 nm (red line) due to 4 F9/2 →6 H15/2 , 4 F9/2 →6 H13/2 , and 4 F9/2 →6 H11/2 intraconfigurational transitions of Dy3+ ions, respectively. The evidence about the site symmetry around Dy3+ ions was examined by considering the ratio of yellow-to-blue emission intensity. The observed critical distance (Rc ) value was ~20.56 Å (≫5 Å), which signified that energy transfer primarily occurred due to multipolar interaction. The obtained coordinates were close to the white region of the Commission Internationale de l'Éclairage chromaticity diagram, which marked a significant milestone in the development of white light-emitting diodes.

Atomically Precise Copper Nanoclusters for Highly Efficient Electroreduction of CO2 towards Hydrocarbons via Breaking the Coordination Symmetry of Cu Site

AbstractWe propose an effective highest occupied d‐orbital modulation strategy engendered by breaking the coordination symmetry of sites in the atomically precise Cu nanocluster (NC) to switch the product of CO2 electroreduction from HCOOH/CO to higher‐valued hydrocarbons. An atomically well‐defined Cu6 NC with symmetry‐broken Cu−S2N1 active sites (named Cu6(MBD)6, MBD=2‐mercaptobenzimidazole) was designed and synthesized by a judicious choice of ligand containing both S and N coordination atoms. Different from the previously reported high HCOOH selectivity of Cu NCs with Cu−S3 sites, the Cu6(MBD)6 with Cu−S2N1 coordination structure shows a high Faradaic efficiency toward hydrocarbons of 65.5 % at −1.4 V versus the reversible hydrogen electrode (including 42.5 % CH4 and 23 % C2H4), with the hydrocarbons partial current density of −183.4 mA cm−2. Theoretical calculations reveal that the symmetry‐broken Cu−S2N1 sites can rearrange the Cu 3d orbitals with as the highest occupied d‐orbital, thus favoring the generation of key intermediate *COOH instead of *OCHO to favor *CO formation, followed by hydrogenation and/or C−C coupling to produce hydrocarbons. This is the first attempt to regulate the coordination mode of Cu atom in Cu NCs for hydrocarbons generation, and provides new inspiration for designing atomically precise NCs for efficient CO2RR towards highly‐valued products.

Atomically Precise Copper Nanoclusters for Highly Efficient Electroreduction of CO2 towards Hydrocarbons via Breaking the Coordination Symmetry of Cu Site.

We propose an effective highest occupied d-orbital modulation strategy engendered by breaking the coordination symmetry of sites in the atomically precise Cu nanocluster (NC) to switch the product of CO2 electroreduction from HCOOH/CO to higher-valued hydrocarbons. An atomically well-defined Cu6 NC with symmetry-broken Cu-S2 N1 active sites (named Cu6 (MBD)6 , MBD=2-mercaptobenzimidazole) was designed and synthesized by a judicious choice of ligand containing both S and N coordination atoms. Different from the previously reported high HCOOH selectivity of Cu NCs with Cu-S3 sites, the Cu6 (MBD)6 with Cu-S2 N1 coordination structure shows a high Faradaic efficiency toward hydrocarbons of 65.5 % at -1.4 V versus the reversible hydrogen electrode (including 42.5 % CH4 and 23 % C2 H4 ), with the hydrocarbons partial current density of -183.4 mA cm-2 . Theoretical calculations reveal that the symmetry-broken Cu-S2 N1 sites can rearrange the Cu 3d orbitals with as the highest occupied d-orbital, thus favoring the generation of key intermediate *COOH instead of *OCHO to favor *CO formation, followed by hydrogenation and/or C-C coupling to produce hydrocarbons. This is the first attempt to regulate the coordination mode of Cu atom in Cu NCs for hydrocarbons generation, and provides new inspiration for designing atomically precise NCs for efficient CO2 RR towards highly-valued products.

The influence of Dy3+ ions doping and annealing temperature on structural, morphological, and spectroscopic properties of lanthanum orthovanadate (LaVO4) material

In the current work, we present the results of nanocrystalline lanthanum orthovanadate (LaVO4) doped with dysprosium ions, which was synthesized by a high-energy ball milling (HEBM) process. Lanthanum, vanadium, and dysprosium oxides were employed as starting reagents. These materials were turned into LaVO4:Dy3+ powder with two polymorphic phases after HEBM and subsequent heating that was carried out in the air in the temperature range from 800 °C to 1200 °C. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and DRS (UV–vis) spectroscopy were used to characterize the obtained Dy-doped LaVO4 powders. The excitation and photoluminescence (PL) emission spectra, and time decay (lifetime) curves of the dysprosium (III) ions in LaVO4 material were measured and analyzed. The influence of annealing temperature and the concentration of dysprosium (III) ions (1%, 2%, and 3% at.) on spectroscopic properties was discussed. The qualitative phase analysis of Dy-doped LaVO4 powders indicated the dominant presence of a monoclinic LaVO4 structure. The presence of the tetragonal solid-solution (La, Dy)VO4 phase was also revealed. The structural transformation consists of an increase of Zr type LaVO4:Dy3+ phase, resulting in a higher structure and site symmetry of t-LaVO4:Dy3+. With increasing Dy3+ content, the relative fraction of the tetragonal (La, Dy)VO4 phase was also increased in all samples. Furthermore, XRD investigations showed that Dy3+ ions were incorporated mainly into the t-(La, Dy)VO4 structure. The increase of the amount of tetragonal phase in polymorphic LaVO4:Dy3+ material results in higher emission intensity caused by more efficient energy transfer from VO43− vanadate group to Dy3+ ions. The average sizes of the m-LaVO4 crystallites, estimated using the Rietveld method, were in a narrow range from 53 to 77 nm. Two main intense emission peaks were observed in the blue (466–495 nm) and yellow (557–594 nm) wavelength ranges and can be ascribed to transitions involving 4F9/2 to the stark split sublevels of 6H15/2 and 6H13/2, respectively. The overall intensity of the emission strongly depends on the annealing temperature. The best results were achieved for powder heated at 1200 °C. The values of the calculated average decay lifetime τavg of the LaVO4 powders doped with 1%, 2%, and 3% at. Dy heated at 800 °C, 1000 °C and 1200 °C were very similar, but one can observe that with increasing heating temperature the average decay lifetime of LaVO4:Dy powders slightly decreased regardless of the Dy concentration.