In situ immobilization of YVO4:Eu phosphor particles on a film of vertically oriented Y2(OH)5Cl·nH2O nanosheets.

A heterostructured photoluminescence 'turn-off' film was developed using vertically oriented LYH:Eu nanosheets as a partial sacrificial layer for isolated YVO4:Eu3+ nanophosphor layers and was used for the convenient detection and removal of Cu2+ ions with excellent sensitivity and recyclability.

Luminescent Carrier, Tb3+-Doped Layered Yttrium Hydroxide, for Delivery Systems.

Layered rare-earth hydroxides (LRHs) with high anion exchangeability between the hydroxocation layers, where a large variety of organic anions can be sheltered, are employed to construct hybrid systems that slowly release active organic ingredients. More importantly, it is possible to endow LRHs with a photoluminescence capability by doping activator ions such as Ce3+, Eu3+, and Tb3+ into matrices. In the present work, we explored Tb3+-doped layered yttrium hydroxide Y1.80Tb0.20(OH)5Cl· nH2O (LYH:Tb) nanosheets as a luminescent carrier for sustained release of salicylic acid (2-hydroxybenzoic acid), an example of nonsteroidal anti-inflammatory drugs and antimicrobial agents. Salicylate (sal) was intercalated into the interlayer gallery of LYH:Tb via a direct ion-exchange reaction. An observed variation in basal spacing suggested that salicylate anions are arranged in an interdigitated bilayer manner in the interlayer space of LYH:Tb. As generally observed in organic/inorganic hybrid systems, the thermal and photostabilities of salicylate were significantly improved after intercalation compared to its free state. The release kinetics of salicylate from sal-LYH:Tb hybrids in a saline solution at pH = 7.4 showed a highly sustained release of salicylate. Among various examined mathematical models, the parabolic diffusion equation best described the cumulative salicylate release. In particular, the salicylate intercalation led to the characteristic 5D4 → 7F J ( J = 6, 5, and 4) green emission of Tb3+ by its sensitization followed by the energy transfer to sal-LYH:Tb, whereas typical blue emission of salicylate was recovered after its release from the interlayer gallery of the LYH:Tb carrier. This green/blue luminescence change behavior provides a useful technique for in situ monitoring of the delivery and release of salicylate at target sites. The sal-LYH:Tb hybrid, with antimicrobial properties, was readily dispersed into a biodegradable polymer, polyvinyl alcohol, to prepare a transparent, UV-shielding, and luminescent composite that is applicable as an antimicrobial polymer to retard or prevent microbial growth.

Layered Yttrium Hydroxide l-Y(OH)3 Luminescent Adsorbent for Detection and Recovery of Phosphate from Water over a Wide pH Range.

Layered yttrium hydroxide, l-Y(OH)3, has been explored as a representative member of the layered rare earth hydroxide family (l-RE(OH)3; RE = rare earths) for removal and recovery of phosphate from aqueous solution. Compared to the hexagonal form, h-Y(OH)3, which has a weakly positive surface charge only at low pH, the layered polymorph composed of hydroxocation layers exhibited a high point of zero charge (pHpzc ∼ 11) and significantly enhanced adsorptive ability for anions over a wide pH range. The Langmuir isotherm model and pseudo-second-order kinetic model were adopted to explain the phosphate adsorption on l-Y(OH)3. This new adsorbent revealed high capacity, efficiency, stability, selectivity, and reusability in adsorption of phosphate from a single electrolyte as well as natural waters containing competing anions. Essentially complete phosphate recovery from aqueous solutions at low phosphate concentrations (2.0 mg of P/L) was demonstrated with an adsorbent dosage of 0.025-0.5 g/L. The adsorption of phosphate was accompanied by an increase in the solution pH, suggesting a release of OH- ions during the adsorption reaction. In particular, when Ce3+ and Tb3+ were co-doped (l-Y(OH)3:Ce,Tb), phosphate adsorption led to the characteristic 5D4 → 7FJ (J = 6, 5, and 4) emissions of Tb3+ under commercial 312 nm UV irradiation. The photoluminescence of phosphate-adsorbed l-Y(OH)3:Ce,Tb provided evidence of the inner-sphere complexing mechanism involving the formation of Y(Ce,Tb)-O-P bonds through which the energy transfer can occur. The "luminescence-on" behavior of l-Y(OH)3:Ce,Tb by phosphate adsorption was employed to detect and recover phosphorus at low concentrations in deionized water, mineral water, tap water, and river water.

Selective Filter Effect Induced by Cu(2+) Adsorption on the Fluorescence of a GdVO4:Eu Nanoprobe.

Human blood contains substantial amounts of metal ions such as Mg(2+), Ca(2+), Fe(2+), Cu(2+), Zn(2+), Cd(2+), Pb(2+), and Al(3+). Most biomedical applications of nanoparticles require understanding the influence of these metal ions because adsorbed metal ions can affect the function of nanoparticles to limit their sensitivity, performance, stability, and/or resolution in applications. In the present work, the adsorption of various metal ions at the surface of GdVO4:Eu nanoparticles was studied to assess their spectral filter effect on the fluorescence of GdVO4:Eu. Due to the negative surface potential, the electrostatic attraction caused an intensive adsorption reaction of GdVO4:Eu nanoparticles with metal cations. Compared to the adsorption of other common metal ions in human blood, the distinct fluorescence quenching of GdVO4:Eu was induced in the presence of Cu(2+) ions. On the basis of the UV-vis absorption spectrum of an aqueous CuCl2 solution and reflectance spectrum of Cu(OH)2, in which the surroundings of Cu(2+) ions are supposedly similar to the hydroxylated surface of GdVO4:Eu nanoparticles, it is proposed that the complementary overlap of the emission band of GdVO4:Eu with the absorption band of Cu(2+) results in the effective filter effect to quench the red emission. Because GdVO4:Eu nanoparticles are attractive candidates for applications as magnetic/fluorescent multimodal nanoprobes, it is important to recognize that the average amount of Cu(2+) ion in human blood is sufficient to interfere with or limit the fluorescence probe function of GdVO4:Eu nanoparticles.

Antenna Effect on the Organic Spacer-Modified Eu-Doped Layered Gadolinium Hydroxide for the Detection of Vanadate Ions over a Wide pH Range.

The excitation of the adsorbed vanadate group led to the red emission arising from the efficient energy transfer to Eu-doped layered gadolinium hydroxide (LGdH:Eu). This light-harvesting antenna effect allowed LGdH:Eu to detect selectively a vanadate in aqueous solution at different pHs. Because vanadate exists in various forms by extensive oligomerization and protonation reactions in aqueous solution depending on pH, it is important to detect a vanadate regardless of its form over a wide pH range. In particular, spacer molecules with long alkyl chains greatly facilitated access of a vanadate antenna into the interlayer surface of LGdH:Eu. The concomitant increase in adsorption capacity of LGdH:Eu achieved a strong antenna effect of vanadate on the red emission from Eu(3+). When a suspension containing LGdH:Eu nanosheets (1.0 g/L) was used, the vanadate concentration down to 1 × 10(-5) M could even be visually monitored, and the detection limit based on the (5)D0 → (7)F2 emission intensity could reach 4.5 × 10(-8) M.

The inner filter effect of Cr(VI) on Tb-doped layered rare earth hydroxychlorides: new fluorescent adsorbents for the simple detection of Cr(VI).

Terbium-doped layered yttrium hydroxychlorides (LYH:xTb) were explored for the simple and convenient detection of Cr(VI) in aqueous solution, where the effective overlap of excitation bands of LYH:xTb with absorption bands of Cr(VI) constructs a new inner filter effect system. The shielding of excitation light for LYH:xTb by adsorbed Cr(VI) was so effective that a feasible detection sensitivity could be achieved.

Oxychloride-hydroxychloride-trihydroxide phase relationships of rare earths in aqueous solution.

Phase studies were undertaken with PbFCl-type rare earth oxychlorides (REOCls), where RE = La-Dy and Y. Specifically, equilibria in REOCl-H2O systems were investigated in an effort to describe the interrelationship of the oxychloride, hydroxychloride, and trihydroxide phases of rare earths in water. When lighter rare earths were employed, REOCls were generally stable in basic media, while acidic solutions readily yielded RE(OH)3 by hydrolysis. However, the systematics of equilibrium established in sufficient amounts of water did not continue across the rare earth series and were not particularly relevant to cases in which the oxychloride phase was added to a volume of water smaller than the critical quantity. Difficulties encountered during initial attempts to investigate the hydrolysis of REOCl required that a special parameter, the dilution ratio (D = volume of water/weight of powder), be used for REOCl-RE2(OH)5Cl·nH2O-RE(OH)3 phase relationships in water at different temperatures. The equilibration of REOCl in solutions of low dilution ratios (D ≤ 0.5 mL/mg) yielded all three phases depending on the nature of the RE, dilution ratio, and temperature. Interestingly, the addition of salt (NaCl) to systems at similar dilution ratios markedly increased the stability of RE2(OH)5Cl·nH2O phases. In contrast, the essential feature of YOCl-water equilibria in the range 0.1 ≤ D ≤ 1.0 mL/mg was characterized by spatial stability of the Y2(OH)5Cl·nH2O structure. In conclusion, the present investigation provides systematic phase diagrams for rare earth oxychloride-water systems that can be used as guidelines for the preparation and application of REOCls and RE2(OH)5Cl·nH2O phases in aqueous media.

Tunable color generation of transparent composite films reinforced with luminescent nanofillers.

A new composite film based on calcined layered rare earth hydroxides and poly(vinyl alcohol) shows a visible light transmittance comparable to that of the pure matrix, highly reinforced mechanical strength as well as tunable photoluminescence in rolled and folded shapes.

The selective antenna effect of tungstate anions for Tb-doped layered yttrium hydroxynitrate.

A simple way to detect and remove trace amounts of WO4(2-) ions from an aqueous solution was demonstrated by their light-harvesting ability and selective excitation energy transfer to a Tb-doped layered yttrium hydroxynitrate matrix.

A layered polymorph of rare earth hydroxides.

A layered polymorph series of rare earth hydroxides has been developed by the conversion of RE2(OH)5Cl·mH2O to RE(OH)3·nH2O (RE = rare earths) with a typical layered structure with interlayer water molecules. A temperature-induced phase transition from the layered polymorph to its hexagonal form is completed at approximately 300 °C.

Directional self-assembly of rare-earth hydroxocation nanosheets and paradodecatungstate anions.

Simply mixing layered rare-earth hydroxide colloidal solutions and paratungstate solution at pH > 7 led to directional self-assembly of rare-earth hydroxide nanosheets and paradodecatungstates. These hybrids exhibit efficient energy transfer from the OMCT band to rare-earth ions in the hydroxide layers as well as highly enhanced f-f transitions.

Thermal decomposition and recovery behaviors of layered gadolinium hydroxychloride.

The thermal behavior of gadolinium hydroxychloride (Gd(2)(OH)(5)Cl·nH(2)O, LGdH) has been closely studied to provide the important factors that should be considered for its high temperature applications. Combined analyses of thermogravimetry-differential scanning calorimetry-mass spectrometry (TG-DSC-MS) showed that, under atmospheric air with a considerable amount of water, the decomposition of LGdH to Gd(2)O(3) is completed at 1050 °C. However, in either dry air or Ar gas, the transformation continued up to around 1300 °C. Thus, the thermal decomposition of LGdH was more influenced by H(2)O than by O(2). FT-IR spectra and X-ray diffraction (XRD) patterns were used to study LGdHs calcined at high temperatures (up to at least 600 °C). Calcined LGdH's ability to intercalate anions into the interlayer space could be recovered by the reconstruction of intralayer structure through rehydration and rehydroxylation. These processes were significantly accelerated at elevated temperatures. The recovery behavior of LGdH was examined in different anionic solutions at different temperatures.

Highly enhanced photoluminescence of a rose-like hierarchical superstructure prepared by self-assembly of rare-earth hydroxocation nanosheets and polyoxomolybdate anions.

Construction of a rose-like hierarchical superstructure composed of rare-earth hydroxide nanosheets and polyoxomolybdates, which was achieved by the self-assembly at room temperature, led to a drastically enhanced photoluminescence.

Superhydrophilic and antireflective La(OH)(3)/SiO(2)-nanorod/nanosphere films.

La(OH)(3) nanorods were self-stacked on the glass slide substrates using an aqueous suspension obtained from the hydrolysis of LaOCl. The key for producing a high optical quality film of La(OH)(3) lies in the preparation of an aqueous suspension in which La(OH)(3) nanorods are well dispersed. These thin-film coatings of La(OH)(3) nanorods led to a significantly reduced reflective losses in the visible region, exhibiting an attractive and potentially useful single-layer antireflection property. Furthermore, La(OH)(3) nanorod layer provides a sufficiently porous and rough surface required to achieve superhydrophilicity. Thus, when SiO(2) nanoparticles of ca. 20nm in diameter were deposited onto La(OH)(3) layer of high roughness, the resulting La(OH)(3)/SiO(2) film demonstrated an interesting nanoporosity-derived superhydrophilicity and antifogging property with no significant loss of antireflective property.

Fabrication of a silica sphere with fluorescent and MR contrasting GdPO4 nanoparticles from layered gadolinium hydroxide.

The delaminated gadolinium hydroxide layers doped with Eu(3+) ions were assembled on the surface of silica spheres and annealed at high temperatures, resulting in the formation of fluorescent and MR active GdPO(4) : Eu nanoparticles at the surface.

Transparent Gd2O3 : Eu phosphor layer derived from exfoliated layered gadolinium hydroxide nanosheets.

The positively charged layered gadolinium hydroxide nanosheets were produced by exfoliation in formamide and was applied to fabricate highly transparent and highly luminescent Gd(2)O(3) : Eu layers on quartz glass by simple evaporation and subsequent annealing.

Synthesis of colloidal aqueous suspensions of a layered gadolinium hydroxide: a potential MRI contrast agent.

A layered gadolinium hydroxychloride (LGdH), [Gd2(OH)5(H2O)x]Cl, was synthesized from an aqueous solution of GdCl3.6H2O. The X-ray diffraction (XRD) and the selected area electron diffraction (SAED) studies showed that this compound crystallizes in the orthorhombic structure (a = 12.88(4) A, b = 7.30(2) A, and c = 8.46(3) A) which is isostructural with [Eu2(OH)5(H2O)x]Cl. Interestingly, this layered material was readily dispersed and led to a stable colloidal nanosheet in aqueous medium. The obtained colloidal solutions were characterized by the evaluation of their stability in acidic solution, their in vitro cytotoxicity, and their magnetic resonance imaging (MRI) relaxation properties. It is reported that the relaxometry analysis of LGdH suspensions exhibits a sufficient contrast effect for T1 weighted magnetic resonance imaging.

Polymorphism in NaSbO3: structure and bonding in metal oxides.

A new polymorph of NaSbO(3) has been synthesized at 10.5 GPa and 1150 degrees C in a uniaxial split sphere anvil type press (USSA-2000) and recovered back to ambient conditions. The high-pressure form of NaSbO(3) adopts an orthorhombically distorted perovskite structure, isostructural with CaTiO(3), GdFeO(3), and NaTaO(3). The space group is Pnma, and the unit cell dimensions are a = 5.43835(6) A, b = 7.66195(8) A, c = 5.38201(5) A. It is a white insulator with an optical band gap of 3.4 eV. This compound represents the first ternary perovskite prepared containing Sb(5+) on the octahedral site. The octahedral tilting distortion in this compound is much larger than expected from ionic radii considerations. The distortion is driven by a second-order Jahn-Teller distortion originating on oxygen that can be traced back to strong Sb-O covalent bonding. A conflict arises between the strong covalent bonding interactions at oxygen that favor a large octahedral tilting distortion and the repulsive Na-O interactions that oppose excessive octahedral tilting. This conflict destabilizes the perovskite topology, thereby stabilizing the ilmenite polymorph under ambient conditions. Analysis of ionic and covalent bonding explains why ASbO(3) and ABiO(3) compositions frequently adopt structures that violate Pauling's rules.