Host Crystal Structure Research Articles

Effect of Host Structure and Concentration on the Luminescence of Eu3+ and Tb3+ in Borate Phosphors

Eu3+ and Tb3+ doped in nanocrystalline InBO3, GdBO3, and LaBO3 having three different morphs of calcite (CaCO3) such as Calcite, Vaterite, and Aragonite, respectively, were synthesized by glycine–nitrate combustion method. Luminescence due to Eu3+ and Tb3+ doped individually as well as simultaneously in these three different morphs of calcite were investigated and compared. Also the effect of concentration of dopant ions on the luminescence was studied. The highest photoluminescence emission intensity was observed for RE0.05M0.95BO3 (RE = Eu3+, Tb3+, M = In, Gd, La) samples. Further increase in doping led to concentration quenching of the luminescence. In case of the co‐doped borates, the energy transfer between the co‐doped rare earth ions was influenced by the host crystal structure. This study reveals that there is remarkable effect of the crystal structure of host and concentration of dopant ions on the luminescence.

Investigation of energy levels and local lattice for LuLiF4: Yb3+ laser crystal

The complete energy matrix of 4f1/4f13 electronic configuration has been established by using the complete (energy matrix) diagonalization method and superposition model. The calculated energy levels agree well with experimental findings. The structure parameters have been determined in the present work and given as follows: R1≈0.23nm, R2≈0.24nm, θ1≈127.58°, θ2≈31.85°. Comparing with the host crystal structure data, the varieties of bond lengths and angles are, respectively, ΔR1=ΔR2=0.0004 nm, Δθ1=1.5° and Δθ2=−0.5°. Thus, there is slightly tetragonal distortion. What is more, the intrinsic parameters are given in A¯2(R0)>A¯4(R0)>A¯6(R0) which are agreement with the results of many studies.

Papermaking Potential of Novel Structured PCC Fillers with Enhanced Refractive Index

While much effort has been focused on optical properties imparted by particle size distribution, shape, and packing of inorganic particles, the refractive index contrasts within the paper matrix have received less attention. PCC fillers can be used as tools for increasing the refractive index contrast, which further improves paper optical properties. We studied the papermaking potential of novel PCC fillers with an enhanced refractive index. PCC samples were fabricated by conventional carbonation method in the presence of refractive-index enhancing additives. We had previously found that introduction of ZnO as fine spots, including nano-sized structures, on host PCC surfaces improved the effective refractive index and optical performance of PCC. Now, we have studied the papermaking potential of this approach in experiments with handsheets using moderate Zn modification. In addition to Zn, we studied the effect of Sr as an additive and found that Sr inclusion alters the host particle morphology and crystal structure. We report effects of such modifications on light scattering coefficient, brightness, opacity, tensile strength, bulk, and porosity of paper, both before and after calendering. Our results suggest beneficial optical properties, as well as combination of light scattering with strength properties, especially in the case of Sr modified filler. Zn modified fillers opened the sheet structure, while Sr structuring closed the sheets. Calendering resulted in reduced bulk with all fillers, while optical properties were maintained with the Sr modified PCC, but reduced benefit was observed in the combination of light scattering and strength. Calendering conditions should therefore be optimized for these fillers. A higher modification degree of the fillers should also be considered to achieve a more significant refractive index contrast.

Crystal Structure and Luminescent Properties of Green Phosphor Ba3Y2(SiO4)3:Eu2+ for LED Applications

Abstract We have developed a new silicate-based phosphor Ba3Y2(SiO4)3:Eu2+ without using expensive raw materials. The host crystal structure was firstly indexed as an orthorhombic-type instead of garnet-type. The phosphor absorbs near-ultraviolet light around 365 nm and emits green light with a peak at about 505 nm, which results from the 5d–4f transition of the Eu2+. The optimum concentration of Eu2+ activator is 4 mol % relative to the Ba2+ content in the Ba3Y2(SiO4)3 host. It is a promising candidate for application in LEDs as a green-emitting color converter.

The influence of some processing conditions on host crystal structure and phosphorescence properties of SrAl 2O 4:Eu 2+, Dy 3+ nanoparticle pigments synthesized by combustion technique

The spectroscopic and host phase properties of SrAl 2O 4:Eu 2+, Dy 3+ phosphors with a series of different initiating combustion temperature, urea concentration as a fuel and critical pH of precursor solution are investigated. The SrAl 2O 4:Eu 2+, Dy 3+ nanoparticle pigments were obtained by exothermic combustion process within less than 5 min. The sample that ignited at initiating combustion temperature of 600 °C exhibits highest intensity emission peak at 517 nm in which the SrAl 2O 4 host phase has the maximum fraction of monoclinic SrAl 2O 4 phase. The excitation spectra consist of 240 and 254 nm broad peaks. The experimental results show that the optimum ratio of urea is 2.5 times higher than theoretical quantities for best emission condition of SrAl 2O 4:Eu 2+, Dy 3+ phosphor particles. The critical pH was obtained about 5.2. The crystallite size of these pigments is about 40 nm before thermal treatment and 62 nm after thermal treatment, respectively.

Crystal structure effect on the ferromagnetic correlations in ZnO with magnetic impurities

We study the ferromagnetism in the compound (Zn,Mn)O within the Haldane–Anderson impurity model by using the quantum Monte Carlo technique and the tight-binding approximation for determining the host band structure and the impurity-host hybridization. This computational approach allows us to determine how the host crystal structure influences the impurity bound state, which plays an important role in the development of the ferromagnetic (FM) correlations between the impurities. We find that the FM correlations are strongly influenced by the crystal structure. In particular, in p-type (Zn,Mn)O, we observe the development of FM correlations with an extended range at low temperatures for wurtzite and zinc-blende crystal structures. However, for the rocksalt structure, no FM correlations are observed between the impurities. In addition, in n-type ZnO with magnetic impurities, the impurity bound state and FM correlations are not found.

C3v-Symmetrical Tribenzotriquinacenes as Hosts for C60 and C70 in Solution and in the Solid State

Various tribenzotriquinacenes (TBTQs), most of which incorporate six functional groups at the periphery of their C3v-symmetrical, rigid and convex-concave molecular framework, have been studied with respect to their ability to form supramolecular complexes with the C60 and C70 fullerenes, either in the solid state or in solution. The hexabromo derivative Br6-TBTQ was cocrystallized with C60 as [Br6-TBTQ<C60 x toluene] but, as studied by UV/vis and (1)H NMR spectroscopy, aggregation in benzene, toluene, or carbon disulfide solutions was not observed. Likewise, in contrast to the related C5v-symmetrical decakis(alkylthio)corannulenes, neither the parent hydrocarbon, nor a related hexamethoxy, or two hexakis(alkylthio) derivatives exhibited color, or complexation-induced chemical shift (CIS) changes with C60 or C70. The novel tris(2,3-thianthreno)triquinacene (o-S2C6H4)3-TBTQ, a TBTQ derivative extended by three 1,2-benzodithiino wings, and synthesized from Br6-TBTQ, was found to form 1:1 complexes with C60 and C70 in both benzene and toluene solutions. Association constants were determined for the respective complexes, viz. (o-S2C6H4)3-TBTQ<C60 (K(assoc) = 977 +/- 56) and (o-S2C6H4)3-TBTQ<C70 (463 +/- 49, both in benzene). The X-ray single crystal and molecular structures of the pure host and of the aggregates [(o-S2C6H4)3-TBTQ<2 C60 x 2.5 chlorobenzene] were also determined.

Luminescence and microstructures of Eu 3+-doped in triple phosphate Ca 8MgR(PO 4) 7 (R = La, Gd, Y) with whitlockite structure

Eu 3+-doped triple phosphate Ca 8MgR(PO 4) 7 (R = La, Gd, Y) was synthesized by the general high temperature solid-state reaction. This phosphor was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and emission spectra. XRD and FT-IR analysis indicated that Ca 8MgR(PO 4) 7 (R = La, Gd, Y) crystallized in single-phase component with whitlockite-like structure (space group R3 c) of β-Ca 3(PO 4) 2. Under the excitation of UV light, the phosphors show bright red emission assigned to the transition ( 5D 0 → 7F 2) at 612 nm. The crystallographic sites of Eu 3+ ions in Ca 8MgR(PO 4) 7 (R = La, Gd, Y) host were discussed on the base of site-selective excitation and emission spectra, luminescence decay and its host crystal structure.

VUV/UV/X-Ray Excited Luminescent Properties of Eu3+ and Pr3+ Doped BiSbO4

Absorption spectra of BiSbO4 are studied. The electronic structure calculated by the DFT shows that BiSbO4 is a semiconductor, with direct band gap 2.96 eV, which is consistent with UV-visible diffuse reflectance experiment. The host lattice emission band is located at 440 nm under VUV excitation. Eu3+ and Pr3+ doped samples have high luminescence efficiency in emitting red and green light, respectively. From the partial density of states, Eu3+ doped emitting spectrum, and the host crystal structure parameters, the relationship between structure and optical properties is discussed. It is found that the Eu3+ ions occupied Bi3+ sites, and there could be an energy transfer from Bi3+ ions to RE3+ ions.

Mechanism of Mutual Incorporation of Branched Chain Amino Acids and Isomorphic Amino Acids in Batch Crystallization

Toshimichi Kamei On BCAA (Branched Chain Amino Acids) crystallization process, impurity amino acids (guest amino acids) are easily incorporated to the host amino acid(a purified amino acid). Because host and guest amino acids have similar molecular structures and physical-chemical properties, therefore, in many cases, it is difficult to separate a host amino acid and a guest amino acid each other in the simple crystallization method (such as cooling or concentration crystallization conducted in water solvent). In above cases, HCl or precipitant is added to the mixed solution of a host and guest amino acid in order to separate them by generating the salt of a host amino acid. (A host amino acid crystallizes as a hydrochloride or precipitant salt.) But this process is complicated because de-hydrochloric acid or deprecipitant process is needed after crystallization to make the products. Therefore, it is thought that development of the simple crystallization method is necessary in order to make a process simpler. In order to develop the simple crystallization method, it is necessary to elucidate the incorporation mechanism of these amino acids at first, and then decide the crystallization condition based on this mechanism. We explored the mutual incorporation tendency of Branched Chain Amino Acids (L-leucine, Lisoleucine, L-valine ) and isomorphic amino acids in cooling crystallization conducted in water solvent. As a result, in most cases, a guest amino acid whose side chain is longer than that of a host amino acid was incorporated easily in a host amino acid. In this case, a solid solution was formed, and the c-axis of a host crystal structure was extended. Also the crystal growth was inhibited. Using these results, a mechanism for mutual incorporation of these amino acids was proposed.

Investigations on Valence-Change Behaviors of Europium Ions in Eu-Doped Aluminate and Silicate Phosphors

Compounds of Sr 3Al 2O 6 : Eu, Sr 4Al 14O 25 : Eu, and BaZnSiO 4 : Eu were synthesized by high-temperature solid state reactions. The doping Eu 3+ ions were partially reduced to Eu 2+ in Sr 4Al 14O 25: Eu and BaZnSiO 4: Eu prepared in an oxidizing atmosphere, N 2 + O 2. However, such an abnormal reduction process could not be performed in Sr 3Al 2O 6 : Eu, which was also prepared in an atmosphere of N 2 + O 2. Moreover, even though Sr 3Al 2O 6: Eu was synthesized in a reducing condition CO, only part of the Eu 3+ ions was reduced to Eu 2+. The existence of trivalent and divalent europium ions was confirmed by photoluminescent spectra. The different valence-change behaviors of europium ions in the hosts were attributed to the difference in host crystal structures. The higher the crystal structure stiffness, the easier the reduction process from Eu 3+ to Eu 2+.

Photoluminescence and Crystal Structure of Green-Emitting Ca3Sc2Si3O12 : Ce3 + Phosphor for White Light Emitting Diodes

We have developed a new oxide-based phosphor , which is applicable as a green-emitting color converter for white light emitting diodes (LEDs). This phosphor absorbs blue light around and emits green luminescence, with a peak wavelength around . It is a promising candidate for application in LEDs as quenching of the phosphor at was smaller than that of yellow phosphor. A white LED with high color rendering was fabricated by combining this phosphor with a blue GaN LED and a red phosphor. The luminescence of this phosphor is derived from the 5d-4f transition of the Ce ion and the luminescence decay curve fit a single exponential function. This phosphor has a garnet-type host crystal structure. X-ray absorption fine structure analysis showed that Ce ions replaced the Ca position of the host crystal as .

Esterification of β-Chitin via Intercalation by Carboxylic Anhydrides

beta-chitin is known to form intercalation complexes with aliphatic alcohols and amines. We found that it also forms complexes with carboxylic anhydrides. When the beta-chitin-acetic anhydride complex was heated to 105 degrees C, the hydroxyl groups of chitin were acetylated by a host-guest reaction, maintaining the host's crystal structure. Structures of complex and acetylated products were analyzed by X-ray diffraction, (13)C CP/MAS NMR, and infrared spectroscopy. The maximum degree of substitution (DS) was close to 1.0, suggesting regioselective esterification at the C6 position of chitin. Partially acetylated beta-chitin with a DS of 0.4 could incorporate various guest species that are difficult to be incorporated by original beta-chitin. In contrast, beta-chitin acetate with a DS of 1 lost the ability to form a complex. Intercalation complexes of beta-chitin with cyclic anhydrides (succinic and maleic) also underwent esterification by heating, and the products with a DS of approximately 1 dissolved in aqueous alkali, apparently as the result of the dissociation of introduced carboxyl groups. These phenomena are potentially useful in controlling the complexation ability of beta-chitin and the preparation of regioselectively esterified chitin derivatives.

Pattern of minor element enrichment in columbites: A synchrotron radiation X-ray fluorescence ( SRXRF) study

The pattern of minor elements incorporation in columbites from granitic pegmatites of Alto Ligonha, Mozambique, was disclosed on the basis of synchrotron radiation X-ray fluorescence (SRXRF) data. Major elements (Fe, Mn, Nb, Ta) were analyzed with an electron microprobe (EPMA). Minor and trace element contents display a common general trend pointing towards the preferential uptake of metals that minimize the stress induced in the host crystal structure by the non-commensurability of cations with distinct valences and ionic radii. The simultaneous incorporation of Ti, Zr, U, Pb, Y and W assures electrostatic equilibrium, being conditioned by the dominant presence of niobium, while Sc concentrates in solid solutions with low Nb / (Nb + Ta) ratios.

Transport and Structural Properties of Pure and Cr Doped Li3VO4.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Perspectives for high resolution and high light output LuAP:Ce crystals

After its introduction in 1994, LuAlO/sub 3/:Ce (LuAP:Ce) encountered problems of 1) low light output, 2) self-absorption of scintillation light, 3) nonproportionality of light output versus energy, and 4) poor energy resolution, and 5) small non-uniform crystals. Studying newly available LuAP:Ce-doped and undoped crystals (from Photonic Materials), we have found that self-absorption is chiefly dependent on the host crystal structure and not on Ce doping. We examined the scintillation properties of these crystals and found 6.8/spl plusmn/0.3% energy resolution for 662 keV for 2 mm/spl times/2 mm /spl times/10 mm pixels. The intrinsic resolution is equal to 2.8/spl plusmn/0.4% at 2360/spl plusmn/120phe/MeV (9800/spl plusmn/500 ph/MeV) light yield. These crystals have nonproportionality of 93/spl plusmn/4% at 16 keV and intrinsic energy resolution close to that of YAP:Ce. Fast components of the scintillation comprise only about half of the light that is emitted in 100 microseconds.

Transport and Structural Properties of Pure and Cr Doped Li3VO4

This study deals with the effects of 5 and 10% chromium additions on the transport and structural properties of Li3VO4. The Cr substitution is easily obtained without impurity phases and does not affect the room- and high-temperature host crystal structure, as evidenced by X-ray powder diffraction and micro-Raman analysis. The EPR signals are interpreted in terms of quantified amounts of Cr ions in 5+ and 3+ valence states. Suitable 7Li and 51V MAS NMR spectra simulations agree with the EPR results about the relative amount of Cr5+ and Cr3+ ions substituted in V5+ and Li+ sites, respectively. The Cr3+ presence on Li site, also suggested by Raman results and Rietveld refinements, requires Li vacancies to maintain the charge neutrality. The p-type conductivity, suggested by the positive thermoelectric power coefficients, significantly increases by the cation doping up to an order of magnitude.

Stacking-fault pyramids formed in perovskite-type niobate nanosheet aggregates under electron irradiation

We have observed stacking-fault pyramids (SFPs) formed as extended defects in (TBA, H)Ca2Nb3O10 perovskite-type nanosheet aggregates (TBA = tetrabutyl-ammonium) under electron irradiation in a transmission electron microscope. Using the classical SFP as reference, characterization of the structure is discussed. However, irradiation-induced SFPs are not stable and quickly transform to loops. The formation under irradiation of SFPs rather than stacking-fault tetrahedra indicates a strong dependence of extended defect structures on the host crystal structure.

Synthesis of New Cyclophane Host Molecules and Crystal Structures of Their Compounds with Hydrocarbon Guests

Three new cyclophane host molecules 2, 4, and 6 are prepared by connecting the oxygen atoms of twoα ,α'–di(4-hydroxyphenyl)-1,4-diisopropylbenzene units with two di-, tetra-, and hexamethylene spacers, respectively. Solid-state structures are determined for host 2 with a hexane guest, host 4 with a toluene guest and a solvating toluene molecule, host 4 with a p-xylene guest,and host 6 with two p-xylene guests.

Electronic state of oxygen in oxide minerals: an XAS study on the influence of cationic environment

The results are reported here of a XAS study of the O K -edge in oxide minerals, focused on triangular ( C 2ν site symmetry) and tetrahedral ( T d , C 2ν and C 1 ) environments involving diverse coordinating cations within four crystal structure types: rutile-type (rutile, pyrolusite and cassiterite), fluorite-type (thorianite), spinel-type (spinel s.s. ) and garnet-type (andradite). Full multiple-scattering calculations are compared to actual spectra with the aim of interpreting pre-edge peaks and post-edge features. Comments are presented on the role of combinations between O 2 p and metal valence bands. It is concluded that the details and the energy of the O K -edge are influenced by the electronic state and coordination geometry of the surrounding cations in connection with the site symmetry constraints of the coordinated oxygen atoms within the host crystal structure.