Guangqiu Shen

Blue–white–orange color-tunable luminescence of Ce3+/Mn2+-codoped NaCaBO3 via energy transfer: potential single-phase white-light-emitting phosphors

Ce3+/Mn2+-codoped NaCaBO3 single-phase color-tunable phosphors were synthesized by solid-state reaction, and their photoluminescence properties were investigated in detail. Under UV excitation, two main emission bands peaking at 400 and 610 nm were realized in the NaCa0.89BO3: 0.01Ce3+, 0.10Mn2+ phosphor on the basis of the energy transfer from Ce3+ to Mn2+ with an efficiency of over 83%. The energy transfer was validated and demonstrated to be a resonant type via a dipole–dipole mechanism, and the critical distance RC values calculated by the quenching concentration method and the spectral overlap method were 22.85 and 19.41 A, respectively. On examining the Mn2+-concentration-dependent photoluminescence properties, it was observed that the emission color could be tuned from blue (0.162, 0.031) to white-light (0.335, 0.259) and eventually to orange (0.489, 0.246) through energy transfer by changing the Ce3+/Mn2+ ratio. Combining a 370 nm UV chip and a single-phase white-emitting NaCa0.96BO3: 0.01Ce3+, 0.03Mn2+ phosphor produced a white light-emitting diode with CIE chromaticity coordinates of (0.326, 0.274) and an excellent color rendering index of 90.7 at a correlated color temperature of 4046 K. These results indicate that the NaCaBO3: Ce3+, Mn2+ phosphors have potential applications as single-phase white-light-emitting phosphor-converted materials for UV-pumped light-emitting diodes.

Application of the nonlinear crystal SrB4O7 for ultrafast diagnostics converting to wavelengths as short as 125 nm

We used non-phase-matched second-harmonic generation (SHG) in the highly nonlinear but low-birefringence crystal SrB4O7 for temporal characterization (autocorrelation) of femtosecond UV pulses to convert these pulses to wavelengths as low as 125 nm, close to the transparency limit of SrB4O7. The sensitivity of this method was approximately 1 microJ at the fundamental for a repetition rate of 1 kHz. We also used SHG at longer wavelengths to estimate the three nonlinear coefficients of SrB4O7.

Crystal structure refinement and luminescence properties of Ce3+ singly doped and Ce3+/Mn2+ co-doped KBaY(BO3)2 for n-UV pumped white-light-emitting diodes

A series of novel Ce3+ singly doped and Ce3+/Mn2+ co-doped color-tunable KBaY(BO3)2 phosphors were synthesized by a high-temperature solid-state reaction, and the crystal structures and luminescence properties were investigated in detail. The crystallographic cation sites occupancy of the doping Ce3+ and Mn2+ ions for KBaY(BO3)2: Ce3+, Mn2+ samples were analyzed by the Rietveld refinement method. It was demonstrated that Ce3+ and Mn2+ ions can both enter into the two types of cation sites in the KBaY(BO3)2 crystal lattice, with a slight tendency of occupancy for Ce3+ on Y3+ ion sites and Mn2+ on the Ba2+/K+ ion sites. By controlling Mn2+ ions content with a fixed Ce3+ concentration, the emission color of the phosphor varied from blue (0.160, 0.150) to pink-white (0.348, 0.272) and eventually to orange (0.490, 0.372). The critical energy transfer distance calculated by the concentration quenching theory was 16.52 A and the energy transfer from Ce3+ to Mn2+ took place via a resonance-type dipole–dipole mechanism. By combining the single-phase KBa0.97Y0.97(BO3)2: 0.01Ce3+, 0.05Mn2+ phosphor with an n-UV 370 nm InGaN chip, a phosphor-converted white LED lamp was successfully fabricated, producing a white light with a warm correlated color temperature of 4710 K and color coordinates of (0.347, 0.307).

The synthesis and structure of a novel 1D copper(II) weak coordination polymer with 2,6-pyridinedicarboxylic acid

A novel copper complex, [Cu(dipic)(H2O)2] n (H2dipic = 2,6-pyridinedicarboxylic acid), was synthesized and its crystal structure determined by X-ray diffraction. The complex has a polymeric structure of infinite one-dimensional (1D) zigzag chains, consisting of six-coordinate Cu(II) units. Each copper(II) ion is in a distorted octahedral environment with a CuNO5 core: two oxygen atoms and one nitrogen atom from one dipic anion, one oxygen atom from an adjacent dipic ligand and two oxygen atoms from coordinated water. Each dipic anion connects two copper ions via a μ2-oxygen atom. The zigzag 1D-chains are linked by extensive hydrogen bonds to form 2D infinite sheets.

Cracking mechanism in CLBO crystals at room temperature

Cesium lithium borate single crystals tend to crack at room temperature in an ambient air atmosphere, which has limited their use in device applications. This study shows that the cracking of high-quality CLBO crystals results from the anisotropic corrosive effect of water vapor in the ambient atmosphere. The directional attack by water molecules at the crystal surface was related to its crystal structure. The crystal quality of CLBO was found to influence the crack propagation velocity.

Highly efficient field emission from large-scale and uniform monolayer graphene sheet supported on patterned ZnO nanorod arrays

A graphene/patterned ZnO (G/PZO) nanorod array composite was successfully fabricated by using the colloidal nanosphere monolayer templating strategy. Compared with graphene/compact ZnO (G/CZO) nanorod arrays, the G/PZO nanorod array composite exhibited a highly efficient and stable field emission with a low turn-on field. The field emission had a strong dependence on the density and the inter-distance of the emitters. By changing the diameter of polystyrene (PS) colloidal nanospheres, optimal emitter inter-distance was obtained. Graphene supported on ZnO nanorod arrays, patterned by an 886 nm PS colloidal nanosphere monolayer, displayed the best field emission with a turn-on electric field of only 6.4 V μm−1 and the field enhancement factor β was 1158. The K point in the Fowler–Nordheim plot demonstrated the electron tunneling mechanism took place in this composite material. The cyclic experiment showed that the field emission of the G/PZO nanorod array composite was of high stability.

Crystal growth and optical properties of a noncentrosymmetric molybdenum tellurite, Na2Te3Mo3O16

Single crystals of Na2Te3Mo3O16, with sizes up to 23 × 5 × 4 mm3, have been successfully grown by the top-seeded solution growth method for the first time. Na2Te3Mo3O16 crystallizes in the noncentrosymmetric monoclinic space group I2 with cell parameters a = 7.3130(15) A, b = 11.236(2) A, c = 8.2171(16) A, and β = 97.26(3)° and Z = 2. The crystal is transparent in the wavelength range of 0.42–5.4 μm. In addition, band structure and density of states calculations for Na2Te3Mo3O16 were carried out using the total-energy code CASTEP, based on density functional theory.

Crystal structure of a new oximato-bridged one-dimension(1D) chain-like copper complex polymer {[Cu4(dmg)2(Hdmg)2(H2dmg)2(H2O)2](ClO4)2}∞

Abstract A novel copper complex polymer {[Cu4(dmg)2(Hdmg)2(H2dmg)2(H2O)2](ClO4)2}∞ (H2dmg=dimethylglyoxime) has been synthesized and its structure was determined by X-ray single crystal diffraction methods. The complex polymer is like a 1D infinite chain with topological type as a sequence of fused rings connected by out-planar CuO bonds, in which oximato groups (NO−) act as two-dentate bridges to link center Cu2+ cations. This structure shows that oximes have great perspective in coordination chemistry and supramolecular polymer chemistry. Molecular structure and spectroscopic properties of the polymer complex were discussed in the article.

Viscosity and IR investigations in the Li2OB2O3 system

The high viscosity in melts of the Li2OB2O3 system makes it very difficult to grow large crystals of lithium triborate. The viscosity and IR characteristics of molten li2OB2O3 system are reported in this paper. When the temperature increases the viscosity of li2OB2O3 system decreases and follows an Arrhenius-type relationship. With an increasing 13203 ratio in Li2OB2O3 melts, the viscosity rises gradually to a maximum with a composition Li2O: 3.513203 then it falls rapidly. In order to find active agents to reduce the viscosity, Na2O, NaCl, LiF, P205, M003, W03 etc oxides were added to Li2OB2O3 samples respectively and investigated using the orthogonal method. The experimental results show that the addition of acidic oxides can significantly decrease the viscosity in the Li2OB2O3 system. For Li2O: 4.513203, an ideal additive agent is 20wt% Li2O:: 2MoO3. Near the composition for crystal growth, the percentage reduction of viscosity is 62.2%. The IR spectra of Li2OB2O3 system revealed that the BO4−/NO3− ratio is reduced in the melt using Li2O: 2MoO3 as an additive. It is proposed that the M003 reduced the concentration of bridging oxygen atoms of BO4−. The change of structure explains the decline in the viscosity. In the crystal structures of lithium triborate, the matrix spaces are so small that larger other cations than Li+ are very difficult to enter the crystal matrix. So the use of additive agents to reduce the viscosity is a possible method if no new phase appears.

Synthesis, crystal structures and luminescent properties of two new Ln(III)-dicarboxylate (Ln=Eu, Tb) complexes exhibiting three dimensional networks

Two new coordination polymers, {[Eu2(L1)3(H2O)2] · H2O} n (1), (Cu(II) ··· Cu(II), [Tb(H2O)]2(L2)3 · 4H2O (2) (H2L1 = succinic acid, H2L2 = glutaric acid) have been hydrothermally synthesized and characterized by elemental analysis, IR, luminescence spectra and single crystal X-ray diffraction. The complexes are constructed by dicarboxylates bridging chains of edge-sharing EuO8(H2O) and TbO8(H2O) polyhedra to form 3D network structures. Complexes 1 and 2 exhibit intense red and green photoluminescence upon UV excitation in the solid state at room temperature.