Rongjian Sa

A white-light-emitting LnMOF with color properties improved via Eu3+ doping: an alternative approach to a rational design for solid-state lighting

The intrinsic white-light-emitting properties of a lanthanide metal-organic framework that approach requirements for solid-state lighting are easily improved by incorporating minute quantities of red-emitting Eu(3+) into the host framework by virtue of the isostructural character of the La(3+) and Eu(3+) compounds and efficient sensitization of ligands toward Eu(3+) ions.

Density functional theory studies on the potential energy surface and hyperpolarizability of polyamidoamide dendrimer

Abstract The potential energy surface and hyperpolarizabilities of the core (G0) and the first generation (G1) of polyamidoamide (PAMAM) dendrimer are studied by using the density functional theory with both the basis sets optimized for B3LYP method and the medium-size polarized GTO/CGTO basis sets for calculations of molecular polarizability. The inversion barrier of G1 is 941.4 cm −1 , which indicates that the back folding of the branches is very easy for this dendrimer construction. It is found that in most cases, the first hyperpolarizabilities β of G1 will increased when the molecular structure is distorted from its equilibrium arrangement. These results provide structural guidelines for the optimization of β by means of changing the dendrimer shape in different solvents.

A highly stable and white-light-emitting Eu(III) MOF

A long π-conjugated organic ligand 2-(2,4-disulfophenyl)imidazo(4,5-f)(1,10)-phenanthroline (H3sfpip) featuring blue-green emission was used to construct Eu(iii) MOFs to obtain a target white-light-emitting LnMOF with no dopant atom in its structure. Two complexes, [Eu(H2O)2(OH)(Hsfpip)]·H2O (1) and [Eu(H2O)(oa)0.5(Hsfpip)]·2H2O (2), were successfully synthesized under similar hydrothermal reaction conditions. The absence or presence of an ancillary ligand such as oxalic acid (oa) showed direct influence on the coordination mode of the Hsfpip linker and in the final topology of the polymeric structure. Complex 1 displays an unstable 2D polymeric structure and weak red luminescence from Eu3+ due to the quenching effect of high-energy O-H oscillators around the inner coordination sphere of the metal center, whereas the introduction of an ancillary ligand such as oxalic acid results in a tight-bonding 3D polymeric structure and an intense white light emission from complex 2. Moreover, due to the skeleton rigidity and robustness of complex 2, the white light emission can be improved via a heating process.

Theoretical studies of nonlinear optical crystals in metal cluster compounds

Theoretical studies and simulations have been applied to explore novel nonlinear optical crystals in metal clusters. The structure-nonlinear optical property relationships of a series of metal cluster molecules have been investigated theoretically within the density functional theory framework. For example, the polarizability and hyperpolarizability of a set of three-nuclear metal cluster compounds of the Mo(W)/Cu(Ag, An) sulfur system are calculated to elucidate the influence of the geometric configuration and the element substitution effect; a set of potential second harmonic generation (SHG) metal cluster crystals are studied and simulated such as the MoAg(2)S5(Py)(PPh3)(2), MoS4Cu4I2(Py)(6) clusters. The results indicate that many of these crystals are promising SHG crystals that may be applied in the infrared (IR) spectroscopic region. The studies are useful to aid in screening, simulating and designing novel nonlinear optical crystals in metal cluster compounds, especially those to be applied in medium/far-IR region

Computation-predicted, stable, and inexpensive single-atom nanocatalyst Pt@Mo2C – an important advanced material for H2 production

The finding that transition metals on Mo2C-supported nanocatalysts are promising for water-gas shift (WGS) reactions at room temperature has generated much excitement. However, the progress achieved with computational chemistry in this area is far behind that of experimental studies. Accordingly, density functional theory (DFT) calculations have been used to design the catalytic activity center structure and study the stabilities and catalytic performances of transition metals doped on β-Mo2C(001) surfaces. A new catalyst that comprises atomically dispersed Pt over Mo2C was designed using DFT. The bimetallic Mo2C surfaces doped with single metal Pt exhibit catalytic activities similar to those of the Pt systems for WGS, while demonstrating the advantages of lower costs and higher thermal stabilities. Importantly, the Pt@Mo2C catalyst is more efficient than the pure Pt catalyst for H2 production under the same reaction conditions. Meanwhile, the density of active sites of Pt@Mo2C(001) for H2 production is considerably increased due to its highly dispersed Pt structure. Therefore, Mo and Pt can synergistically increase H2 production. These findings are significantly beneficial for establishing the relationship between the structure and characteristics of the catalyst, understanding the catalytic activities of single-atom catalysts, and gaining insight into the feasibility of developing substitutes for expensive noble metal catalysts.

Large hyperpolarizabilities of trinuclear transition metal clusters [MAg2X4(C5H5NS)(PPh3)2]·CH2Cl2 (M = Mo, W; X = S, Se): a DFT study

Static and dynamic first hyperpolarizabilities have been studied by a DFT approach for a series of trinuclear heterometallic transition metal molecular clusters, [MAg2X4(C5H5NS)(PPh3)2]·CH2Cl2 (M = Mo, W; X = S, Se) with incomplete cubane-like configurations. Their nonlinear optical nature has been analyzed by using a two-level model. The large hyperpolarizabilities of about 100 × 10−30 esu of these metal clusters are generated by intermolecular charge transfers from the metal core to the pyridine-2-thiol ligand as well as by intramolecular charge transfers within the metal core. The conjoint effects of stereo π (3D) conjugation of the metal core and planar π (2D) conjugation of the C5H5NS ligand enhance these hyperpolarizabilities, while the presence of CH2Cl2 has a negative effect by lowering them. Since these complexes are all crystallized in noncentrosymmetric configurations, they are promising candidates as IR second-order nonlinear optical transition metal coordinated materials.

Improved thermoelectric power factor and conversion efficiency of perovskite barium stannate

In the pursuit of high thermoelectric conversion efficiency, both high operating temperature and high figure of merit ZT are desirable. Thermoelectric materials used in high-temperature power generation are still in great demand. Here we demonstrate the n-type doped barium stannate (BaSnO3) behaves as a robust candidate, as a high-temperature thermoelectric material, due to its ultrahigh power factor and excellent structural and chemical stability. A systematic calculation focused on the geometric, electronic and thermoelectric transport properties of BaSnO3 is performed by using density functional theory combined with Boltzmann transport theory. It can be noticed that the electrical conductivity of BaSnO3 is improved dramatically when it is n-type doped, resulting from the small effective mass and extraordinary high mobility. The power factor maximum reaches 1.5 × 10−3 W m−1 K−2 at 1200 K with the optimal carrier concentration 1.6 × 1019 cm−3, which suggests the great potential of BaSnO3 as an n-type high temperature thermoelectric material.

A comprehensive understanding of water photooxidation on Ag3PO4 surfaces

The oxygen evolution reaction (OER) is known to be the bottleneck of water-splitting. Ag3PO4 is a highly efficient visible light photocatalyst for dye degradation and water oxidation to O2, with a higher OER rate than BiVO4 and WO3. Despite extensive studies on Ag3PO4, the surface properties including surface electronic states, reaction sites and mechanisms of OER on Ag3PO4 surfaces are not clear at present. Herein, we reported a comparative first-principles density functional theory study of the bulk, surface properties and the mechanism of OER on the three primary low index facets of Ag3PO4: (100), (110) and (111). We revealed for the first time that the rate-limiting step of the OER on Ag3PO4 (100), (110) and (111) surfaces is the dehydrogenation of HO* (HO* → O* + H+ + e−), which is different from most reported metal oxides and nitrides like TiO2 and g-C3N4. The OER process on the (100) surface tends to proceed by following a different mechanism as that on the (110) and (111) surfaces. The illumination of the Ag3PO4 (100), (110), and (111) surfaces with solar light provides enough overpotential for the OER to proceed spontaneously. In particular, the free energy change of removal of the first proton from water on the Ag3PO4 (111) surface is much lower than that on (100) and (110) surfaces, giving an explanation for the experimentally observed higher catalytic activity of the (111) surface. The exposed phosphorus atoms on the Ag3PO4 (111) surface promote the dehydrogenation of H2O and suppress the formation of mid-gap states. Our results are profound for understanding the underlying mechanism of the photocatalytic water oxidation process occurring on Ag3PO4 surfaces, and serve as a foundation for developing new high-performance Ag3PO4 based photocatalysts for water splitting and organic contaminant decomposition.

Receding mechanism of NLO response of polyanion [M8O26]4− (M = Cr, Mo, W) and the closed loops theory analysis

The second hyperpolarizability of six octa-poly-oxo anions [M8O26]4− (M = Cr, Mo, W) were studied by DFT/TDDFT method. All of the six high symmetric anions possess moderately large γ values and the results present a receding sign of the third order NLO response as the metal element changes from Mo to Cr and W. For further knowledge of the third order NLO response mechanism, the electronic properties were studied by DFT method. The results suggest that the NLO property is closely related to the orbital closed loops of the unique electronic structure of the polyanion cage, and the direct relationship of the third order NLO response with the number and shape of the loops is presented. It is the first attempt of the analysis of NLO response mechanism by “orbital closed loops theory”.

Screening novel candidates for mid-IR nonlinear optical materials from I3–V–VI4 compounds

Although numerous superior nonlinear optical (NLO) crystals for the UV-vis to the near-infrared (IR) region have been established, the development of an efficient NLO material capable of broadband second harmonic generation (SHG) in the mid-IR region is still a big challenge. In this work, we performed hybrid functional calculations to accurately assess the mid-IR NLO capabilities of a group of I3–V–VI4 compounds (with I = Ag or Cu, V = P or As, and VI = S or Se). The linear and nonlinear optical properties of these crystals were predicted and analyzed. This group of compounds display moderate optical anisotropy of refraction (0.1 > Δn > 0.03) to fulfill the phase-matching conditions. In particular, the static SHG coefficients of Cu3AsS4, Ag3PSe4 and Cu3PSe4 are predicted to be about twice that of the benchmark AgGaSe2. A detailed analysis of their precise electronic structures and local dipole moments suggests that it is the coupling of the large dipole moment vector of the constituent asymmetry [I–VI4] tetrahedron and the strong covalent character between V and VI ions that contributes to the large SHG response. These candidates would promote the development of the mid-IR NLO functional materials.