Study on optical properties of rare-earth ions in nanocrystalline monoclinic SrAl2O4: Ln (Ln = Ce3+, Pr3+, Tb3+)

SrAl(2)O(4): Ln (Ln = Ce(3+), Pr(3+), Tb(3+)) nanocrystals have been synthesized by the combustion method. The results of XRD indicated that the resulting SrAl(2)O(4): Ln (Ln = Ce(3+), Pr(3+), Tb(3+)) nanocrystals have a reduced and distorted monoclinic lattice compared with bulk materials. The spectral properties are measured, and it is found that the excitation peaks of 5d energy levels red shift in nanocrystals in contrast to that in bulk crystals. The mechanism of spectra and energy changes is investigated. The order of the degree of red shift for nano SrAl(2)O(4): Ln (Ln = Ce(3+), Pr(3+), Tb(3+)) crystals is Pr(3+) > Ce(3+) > Tb(3+), which is in good agreement with our predicted results.     

Magnetism of cyano-bridged hetero-one-dimensional Ln3+-M3+ complexes (Ln3+ = Sm,Gd, Yb; M3+ = FeLS,Co)

The reaction of Ln(NO(3))(3).aq with K(3)[Fe(CN)(6)] or K(3)[Co(CN)(6)] and 2,2'-bipyridine in water led to five one-dimensional complexes: trans-[M(CN)(4)(mu-CN)(2)Ln(H(2)O)(4) (bpy)](n)().XnH(2)O.1.5nbpy (M = Fe(3+) or Co(3+); Ln = Sm(3+), Gd(3+), or Yb(3+); X = 4 or 5). The structures for [Fe(3)(+)-Sm(3+)] (1), [Fe(3)(+)-Gd(3+)] (2), [Fe(3)(+)-Yb(3+)] (3), [Co(3)(+)-Gd(3+)] (4), and [Co(3)(+)-Yb(3+)] (5) have been solved; they crystallize in the triclinic space P1 and are isomorphous. The [Fe(3+)-Sm(3+)] complex is a ferrimagnet, its magnetic studies suggesting the onset of weak ferromagnetic 3-D ordering at 3.5 K. The [Fe(3+)-Gd(3+)] interaction is weakly antiferromagnetic. The isotropic nature of Gd(3+) allowed us to evaluate the exchange interaction (J = 0.77 cm(-)(1)).     

Lanthanide(III) and group 13 metal ion complexes of tripodal amino phosphinate ligands

The tripodal amino-phosphinate ligands, tris(4-(phenylphosphinato)-3-benzyl-3-azabutyl)amine (H(3)ppba.2HCl.H(2)O) and tris(4-(phenylphosphinato)-3-azabutyl)amine (H(3)ppa.HCl.H(2)O) were synthesized and reacted with Al(3+), Ga(3+), In(3+) and the lanthanides (Ln(3+)). At 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(3)ppba)(2)](3+)(M = Al(3+), Ga(3+), In(3+), Ho(3+)-Lu(3+)) were isolated. The bicapped [Ga(H(3)ppba)(2)](NO(3))(2)Cl.3CH(3)OH was structurally characterized and was shown indirectly by various techniques to be isostructural with the other [M(H(3)ppba)(2)](3+) complexes. Also, at 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)(2)](5+)(M = La(3+)-Tb(3+)) were characterized, and the X-ray structure of [Gd(H(4)ppba)(2)](NO(3))(4)Cl.3CH(3)OH was determined. At 1 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)](4+)(M = La(3+)-Er(3+)) were isolated and characterized. Elemental analysis and spectroscopic evidence supported the formation of a 1 : 1 monocapped complex. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+), complex of the type [Ga(ppa)].3H(2)O was obtained. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+) a neutral complex [Ga(ppa)].3H(2)O was obtained. The formation of an encapsulated 1 : 1 complex is supported by elemental analysis and spectroscopic evidence.     

Hydrothermal synthesis, dimension evolution and luminescence properties of tetragonal LaVO4:Ln (Ln = Eu3+, Dy3+, Sm3+) nanocrystals

Well-defined 1D and 3D t-LaVO(4):Ln (Ln = Eu(3+), Dy(3+), Sm(3+)) nanocrystals with regular and uniform shapes were synthesized through a simple hydrothermal route assisted by disodium ethylenediaminetetraacetic acid (Na(2)EDTA). X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), as well as kinetic decay curves were employed to characterize the samples. The results show that the reaction time, pH value of the initial solution, and Na(2)EDTA/La(3+) molar ratio all have an important influence on the dimension and shapes of the final products. By introducing the "splitting mechanism" to the dimension and morphology evolution process from one-dimensional (1D) to three-dimensional (3D) t-LaVO(4) crystals, the nucleation and crystal growth processes were well demonstrated. The Ln(3+) ions doped t-LaVO(4) samples exhibit respective bright red, blue-white and orange luminescence of Eu(3+), Dy(3+), and Sm(3+) under ultraviolet excitation, and have potential application in the fields of colour display, UV laser and biomedicine. The results not only expand the knowledge of the properties of lanthanide orthovanadates luminescence, but also contribute to the principles of the crystal growth and dimension transition of this kind of inorganic material.     

Facile synthesis and multicolor luminescent properties of uniform Lu2O3:Ln (Ln=Eu3+, Tb3+, Yb3+/Er3+, Yb3+/Tm3+, and Yb3+/Ho3+) nanospheres

Multicolor Lu(2)O(3):Ln (Ln=Eu(3+), Tb(3+), Yb(3+)/Er(3+), Yb(3+)/Tm(3+), and Yb(3+)/Ho(3+)) nanocrystals (NCs) with uniform spherical morphology were prepared through a facile urea-assisted homogeneous precipitation method followed by a subsequent calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectrum (EDS), Fourier transformed infrared (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), and photoluminescence (PL) spectra as well as kinetic decays were employed to characterize these samples. The XRD results reveal that the as-prepared nanospheres can be well indexed to cubic Lu(2)O(3) phase with high purity. The SEM images show the obtained Lu(2)O(3):Ln samples consist of regular nanospheres with the mean diameter of 95 nm. And the possible formation mechanism is also proposed. Upon ultraviolet (UV) excitation, Lu(2)O(3):Ln (Ln=Eu(3+) and Tb(3+)) NCs exhibit bright red (Eu(3+), (5)D(0)→(7)F(2)), and green (Tb(3+), (5)D(4)→(7)F(5)) down-conversion (DC) emissions. Under 980 nm NIR irradiation, Lu(2)O(3):Ln (Ln=Yb(3+)/Er(3+), Yb(3+)/Tm(3+), and Yb(3+)/Ho(3+)) NCs display the typical up-conversion (UC) emissions of green (Er(3+), (4)S(3/2),(2)H(11/2)→(4)I(15/2)), blue (Tm(3+), (1)G(4)→(3)H(6)) and yellow-green (Ho(3+), (5)F(4), (5)S(2)→(5)I(8)), respectively.     

Synthesis and characterization of heterodinuclear Ln(3+)-Fe3+ and Ln(3+)-Co3+ complexes,bridged by cyanide ligand (Ln3+ = lanthanide ions). Nature of the magnetic interaction in the Ln(3+)-Fe3+ complexes

The reaction of Ln(NO3)3.aq with K3[Fe(CN)6] or K3[Co(CN)6] in N,N'-dimethylformamide (DMF) led to 25 heterodinuclear [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O and [Ln(DMF)4(H2O)3(mu-CN)Co(CN)5].nH2O complexes (with Ln = all the lanthanide(III) ions, except promethium and lutetium). Five complexes (Pr(3+)-Fe3+), (Tm(3+)-Fe3+), (Ce(3+)-Co3+), (Sm(3+)-Co3+), and (Yb(3+)-Co3+) have been structurally characterized; they crystallize in the equivalent monoclinic space groups P21/c or P21/n. Structural studies of these two families show that they are isomorphous. This relationship in conjunction with the diamagnetism of the Co3+ allows an approximation to the nature of coupling between the iron(III) and the lanthanide(III) ions in the [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O complexes. The Ln(3+)-Fe3+ interaction is antiferromagnetic for Ln = Ce, Nd, Gd, and Dy and ferromagnetic for Ln = Tb, Ho, and Tm. For Ln = Pr, Eu, Er, Sm, and Yb, there is no sign of any significant interaction. The isotropic nature of Gd3+ helps to evaluate the value of the exchange interaction.     

Bifunctional Mixed-Lanthanide Cyano-Bridged Coordination Polymers Ln(0.5)Ln'(0.5)(H(2)O)(5)[W(CN)(8)] (Ln/Ln' = Eu(3+)/Tb(3+), Eu(3+)/Gd(3+), Tb(3+)/Sm(3+))

A new family of mixed-lanthanide cyano-bridged coordination polymers Ln(0.5)Ln'(0.5)(H(2)O)(5)[W(CN)(8)] (where Ln/Ln' = Eu(3+)/Tb(3+), Eu(3+)/Gd(3+), and Tb(3+)/Sm(3+)) containing two lanthanide and one transition metal ions were obtained and characterized by X-ray diffraction, photoluminescence spectroscopy, magnetic analyses, and theoretical computation. These compounds are isotypical and crystallize in the tetragonal system P4/nmm forming two-dimensional grid-like networks. They present a magnetic ordering at low temperature and display the red Eu(3+) ((5)D(0) → (7)F(0-4)) and green Tb(3+) ((5)D(4) → (7)F(6-2)) characteristic photoluminescence. The Tb(0.5)Eu(0.5)(H(2)O)(5)[W(CN)(8)] compound presents therefore green and red emission and shows Tb(3+)-to-Eu(3+) energy transfer.     

Synthesis, structure, and thermally stable luminescence of Eu(2+)-doped Ba2Ln(BO3)2Cl (Ln = Y, Gd and Lu) host compounds

A new family of chloroborate compounds, which was investigated from the viewpoint of rare earth ion activated phosphor materials, have been synthesized by a conventional high temperature solid-state reaction. The crystal structure and thermally stable luminescence of chloroborate phosphors Ba(2)Ln(BO(3))(2)Cl:Eu(2+) (Ln = Y, Gd, and Lu) have been reported in this paper. X-ray diffraction studies verify the successful isomorphic substitution for Ln(3+) sites in Ba(2)Ln(BO(3))(2)Cl by other smaller trivalent rare earth ions, such as Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb. The detailed structure information for Ba(2)Ln(BO(3))(2)Cl (Ln = Y, Gd, and Lu) by Rietveld analysis reveals that they all crystallize in a monoclinic P2(1)/m space group. These compounds display interesting and tunable photoluminescence (PL) properties after Eu(2+)-doping. Ba(2)Ln(BO(3))(2)Cl:Eu(2+) phosphors exhibit bluish-green/greenish-yellow light with peak wavelengths at 526, 548, and 511 nm under 365 UV light excitation for Ba(2)Y(BO(3))(2)Cl:Eu(2+), Ba(2)Gd(BO(3))(2)Cl:Eu(2+), and Ba(2)Lu(BO(3))(2)Cl:Eu(2+), respectively. Furthermore, they possess a high thermal quenching temperature. With the increase of temperature, the emission bands show blue shifts with broadening bandwidths and slightly decreasing emission intensities. It is expected that this series of chloroborate phosphors can be used in white-light UV-LEDs as a good wavelength-conversion phosphor.     

The CsLnMSe3 semiconductors (Ln = rare-earth element,Y; M = Zn,Cd, Hg)

CsLnCdSe(3) (Ln = Ce, Pr, Sm, Gd, Tb, Dy, Y) and CsLnHgSe(3) (Ln = La, Ce, Pr, Nd, Sm, Gd, Y) have been synthesized at 1123 K. These isostructural materials crystallize in the layered KZrCuS(3) structure type in the orthorhombic space group Cmcm and are group X extensions of the previously characterized Zn compounds. The structure is composed of two-dimensional [LnMSe(3)] layers that stack perpendicular to [010] and are separated by layers of face- and edge-sharing CsSe(8) bicapped trigonal prisms. Because there are no Se-Se bonds in the structure of CsLnMSe(3) (M = Zn, Cd, Hg), the formal oxidation states of Cs/Ln/M/Se are 1+/3+/2+/2-. CsSmHgSe(3) does not adhere to the Curie-Weiss law, whereas CsCeHgSe(3) and CsGdHgSe(3) are Curie-Weiss paramagnets with micro (eff) values of 2.77 and 7.90 micro (B), corresponding well with the theoretical values of 2.54 and 7.94 micro (B) for Ce(3+) and Gd(3+), respectively. Single-crystal optical absorption measurements were performed with polarized light perpendicular to the (010) and (001) crystal faces of these materials. The band gaps of the (010) crystal faces range from 1.94 eV (CsCeHgSe(3)) to 2.58 eV (CsYCdSe(3)) whereas those of the (001) crystal faces span the range 2.37 eV (CsSmHgSe(3)) to 2.54 eV (CsYCdSe(3) and CsYHgSe(3)). The largest band gap variation between crystal faces is 0.06 eV for CsYCdSe(3). Theoretical calculations for CsYMSe(3) indicate that these materials are direct band gap semiconductors whose colors and optical band gaps are dependent upon the orbitals of Y, M, and Se.     

Uniform hollow Lu2O3:Ln (Ln = Eu3+, Tb3+) spheres: facile synthesis and luminescent properties

Uniform hollow Lu(2)O(3):Ln (Ln = Eu(3+), Tb(3+)) phosphors have been successfully prepared via a urea-assisted homogeneous precipitation method using carbon spheres as templates, followed by a subsequent calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), photoluminescence (PL) spectra, cathodoluminescence (CL) spectra, kinetic decays, quantum yields (QY), and UV-visible diffuse reflectance spectra were employed to characterize the samples. The results show that hollow Lu(2)O(3):Ln spheres can be indexed to cubic Gd(2)O(3) phase with high purity. The as-prepared hollow Lu(2)O(3):Ln phosphors are confirmed to be uniform in shape and size with diameter of about 300 nm and shell thickness of approximate 20 nm. The possible formation mechanism of evolution from the carbon spheres to the amorphous precursor and to the final hollow Lu(2)O(3):Ln microspheres has been proposed. Upon ultraviolet (UV) and low-voltage electron beams excitation, the hollow Lu(2)O(3):Ln (Ln = Eu(3+), Tb(3+)) spheres exhibit bright red (Eu(3+), (5)D(0)-(7)F(2)) and green (Tb(3+), (5)D(4)-(7)F(5)) luminescence, which may find potential applications in the fields of color display and biomedicine.     

Electrospinning synthesis and luminescence properties of one-dimensional La(9.33)(SiO4)6O2: Ln3+ (Ln = Ce, Eu, Tb) microfibers

One-dimensional La(9.33)(SiO(4))(6)O(2): Ln(3+) (Ln = Ce, Eu, Tb) microfibers were fabricated by a simple and cost-effective electrospinning method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) and low voltage cathodoluminescence (CL) as well as kinetic decay were used to characterize the resulting samples. SEM and TEM results indicated that the diameter of the microfibers annealed at 1000 °C for 3 h was 200-245 nm. The microfibers were further composed of fine and closely linked nanoparticles. La(9.33)(SiO(4))(6)O(2): Ln(3+) (Ln = Ce, Eu, Tb) phosphors showed the characteristic emission of Ce(3+) (5d → 4f), Eu(3+) ((5)D(0)→(7)F(J)) and Tb(3+) ((5)D(3,4)→(7)F(J)) under ultraviolet excitation and low-voltage electron beams (3-5 kV) excitation. An energy transfer from Ce(3+) to Tb(3+) was observed in the La(9.33)(SiO(4))(6)O(2): Ce(3+), Tb(3+) phosphor under ultraviolet excitation and low-voltage electron beam excitation. Luminescence mechanisms were proposed to explain the observed phenomena. Blue, red and green emission can be realized in La(9.33)(SiO(4))(6)O(2): Ln(3+) (Ln = Ce, Eu, Tb) microfibers by changing the doping ions. So the La(9.33)(SiO(4))(6)O(2): Ln(3+) (Ln = Ce, Eu, Tb) phosphors have potential applications in full-color field emission displays.     

Luminescence properties and quenching mechanisms of Ln(Tf2N)3 complexes in the ionic liquid bmpyr Tf2N

The emission properties, including luminescence lifetimes, of the lanthanide complexes Ln(Tf(2)N)(3) (Tf(2)N = bis(trifluoromethanesulfonyl)amide); Ln(3+) = Eu(3+), Tm(3+), Dy(3+), Sm(3+), Pr(3+), Nd(3+), Er(3+)) in the ionic liquid bmpyr Tf(2)N (bmpyr = 1-n-butyl-1-methylpyrrolidinium) are presented. The luminescence quantum efficiencies, η, and radiative lifetimes, τ(R), are determined for Eu(3+)((5)D(0)), Tm(3+)((1)D(2)), Dy(3+)((4)F(9/2)), Sm(3+)((4)G(5/2)), and Pr(3+)((3)P(0)) emission. The luminescence lifetimes in these systems are remarkably long compared to values typically reported for Ln(3+) complexes in solution, reflecting weak vibrational quenching. The 1.5 μm emission corresponding to the Er(3+) ((4)I(13/2)→(4)I(15/2)) transition, for example, exhibits a lifetime of 77 μs. The multiphonon relaxation rate constants are determined for 10 different Ln(3+) emitting states, and the trend in multiphonon relaxation is analyzed in terms of the energy gap law. The energy gap law does describe the general trend in multiphonon relaxation, but deviations from the trend are much larger than those normally observed for crystal systems. The parameters determined from the energy gap law analysis are consistent with those reported for crystalline hosts. Because Ln(3+) emission is known to be particularly sensitive to quenching by water in bmpyr Tf(2)N, the binding properties of water to Eu(3+) in solutions of Eu(Tf(2)N)(3) in bmpyr Tf(2)N have been quantified. It is observed that water introduced into these systems binds quantitatively to Ln(3+). It is demonstrated that Eu(Tf(2)N)(3) can be used as a reasonable internal standard, both for monitoring the dryness of the solutions and for estimating the quantum efficiencies and radiative lifetimes for visible-emitting [Ln(Tf(2)N)(x)](3-x) complexes in bmpyr Tf(2)N.     

Luminescence tuning of imidazole-based lanthanide(III) complexes [Ln = Sm, Eu, Gd, Tb, Dy

To tune the lanthanide luminescence in related molecular structures, we synthesized and characterized a series of lanthanide complexes with imidazole-based ligands: two tripodal ligands, tris{[2-{(1-methylimidazol-2-yl)methylidene}amino]ethyl}amine (Me(3)L), and tris{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(3)L), and the dipodal ligand bis{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(2)L). The general formulas are [Ln(Me(3)L)(H(2)O)(2)](NO(3))(3)·3H(2)O (Ln = 3+ lanthanide ion: Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)), [Ln(H(3)L)(NO(3))](NO(3))(2)·MeOH (Ln(3+) = Sm (6), Eu (7), Gd (8), Tb (9), and Dy (10)), and [Ln(H(2)L)(NO(3))(2)(MeOH)](NO(3))·MeOH (Ln(3+) = Sm (11), Eu (12), Gd (13), Tb (14), and Dy (15)). Each lanthanide ion is 9-coordinate in the complexes with the Me(3)L and H(3)L ligands and 10-coordinate in the complexes with the H(2)L ligand, in which counter anion and solvent molecules are also coordinated. The complexes show a screw arrangement of ligands around the lanthanide ions, and their enantiomorphs form racemate crystals. Luminescence studies have been carried out on the solid and solution-state samples. The triplet energy levels of Me(3)L, H(3)L, and H(2)L are 21?000, 22?700, and 23?000 cm(-1), respectively, which were determined from the phosphorescence spectra of their Gd(3+) complexes. The Me(3)L ligand is an effective sensitizer for Sm(3+) and Eu(3+) ions. Efficient luminescence of Sm(3+), Eu(3+), Tb(3+), and Dy(3+) ions was observed in complexes with the H(3)L and H(2)L ligands. Ligand modification by changing imidazole groups alters their triplet energy, and results in different sensitizing ability towards lanthanide ions.     

YF3:Ln3+ (Ln = Ce, Tb, Pr) submicrospindles: hydrothermal synthesis and luminescence properties

YF(3):Ln(3+) (Ln = Ce, Tb, Pr) microspindles were successfully fabricated by a facile hydrothermal method. X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), lifetimes, photoluminescence (PL) and low-voltage cathodoluminescence (CL) were used to characterize the resulting samples. The lengths and diameters of YF(3):0.02Ce(3+) microspindles are around 760 nm and 230 nm, respectively. Adding dilute acid and trisodium citrate (Cit(3-)) are essential for obtaining YF(3) microspindles. A potential formation mechanism for YF(3) microspindles has been presented. PL spectroscopy investigations show that YF(3):Ce(3+) and YF(3):Tb(3+) microcrystals exhibit the characteristic emission of Ce(3+) 5d → 4f and Tb(3+ 5)D(4)→(7)F(J) (J = 6-3) transitions, respectively. In addition, the energy transfer from Ce(3+) to Tb(3+) was investigated in detail for YF(3):Ce(3+), Tb(3+) microspindles. Under the excitation of electron beams, YF(3):Pr(3+) show quantum cutting emission and YF(3):Ce(3+), Tb(3+) phosphors exhibit more intense green emission than the commercial phosphor ZnO:Zn.     

Metal-to-ligand charge-transfer sensitisation of near-infrared emitting lanthanides in trimetallic arrays M2Ln (M=Ru, Re or Os; Ln=Nd, Er or Yb)

The new pro-ligand 4-methyl-4'-(carbonylamino(2-(tert-butoxycarbonylamino)ethyl))-2,2'-bipyridyl (L1) has been prepared and used to synthesise the complex fac-Re(I)Cl(CO)3(L1) 1 and the complex salts [M(II)(bipy)2(L1)](PF6)2 (M=RuII 8 or OsII 15). Deprotection with trifluoroacetic acid affords the amine-functionalised derivatives fac-Re(I)Cl(CO)3(L2) 2, [M(II)(bipy)2(L2)](PF6)2 (M=RuII 9 or OsII 16) which react with the dianhydride of diethylenetriamine pentaacetic acid (DTPA) to give the binuclear complex {fac-Re(I)Cl(CO)3}2(L3) 3 and the complex salts [{M(II)(bipy)2}2(L3)](PF6)4 (M = RuII 10 or OsII 17). The latter react with salts Ln(OTf)3 to afford a series of 12 heterotrimetallic compounds that contain a lanthanide (Ln) ion in the DTPA binding site; {fac-Re(I)Cl(CO)3}2(L3)LnIII (Ln=Nd 4, Er 5, Yb 6 or Y 7) and [{M(II)(bipy)2}2(L3)LnIII](PF6)(OTf)3 (M=RuII, Ln=Nd 11, Er 12, Yb 13 or Y 14; M=OsII, Ln=Nd 18, Er 19, Yb 20 or Y 21). All of these trimetallic species display absorption bands ascribed to metal-to-ligand charge-transfer (MLCT) excitations, and luminescence measurements show that these excited states can be used to sensitise near-infrared emission from LnIII (Ln=Nd, Er or Yb) ions. Single crystal X-ray structures of L1 and [RuII(bipy)2(L2H)](H2PO4)3.(CH3)2CO.0.8H2O were obtained, the latter revealing the presence of H2PO4- counter anions, the source of which is presumed to be hydrolysis of PF6- ions.     

General synthesis and structural evolution of a layered family of Ln8(OH)20Cl4 x nH2O (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Y)

The synthesis process and crystal structure evolution for a family of stoichiometric layered rare-earth hydroxides with general formula Ln(8)(OH)(20)Cl(4) x nH(2)O (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Y; n approximately 6-7) are described. Synthesis was accomplished through homogeneous precipitation of LnCl(3) x xH(2)O with hexamethylenetetramine to yield a single-phase product for Sm-Er and Y. Some minor coexisting phases were observed for Nd(3+) and Tm(3+), indicating a size limit for this layered series. Light lanthanides (Nd, Sm, Eu) crystallized into rectangular platelets, whereas platelets of heavy lanthanides from Gd tended to be of quasi-hexagonal morphology. Rietveld profile analysis revealed that all phases were isostructural in an orthorhombic layered structure featuring a positively charged layer, [Ln(8)(OH)(20)(H(2)O)(n)](4+), and interlayer charge-balancing Cl(-) ions. In-plane lattice parameters a and b decreased nearly linearly with a decrease in the rare-earth cation size. The interlamellar distance, c, was almost constant (approximately 8.70 A) for rare-earth elements Nd(3+), Sm(3+), and Eu(3+), but it suddenly decreased to approximately 8.45 A for Tb(3+), Dy(3+), Ho(3+), and Er(3+), which can be ascribed to two different degrees of hydration. Nd(3+) typically adopted a phase with high hydration, whereas a low-hydration phase was preferred for Tb(3+), Dy(3+), Ho(3+), Er(3+), and Tm(3+). Sm(3+), Eu(3+), and Gd(3+) samples were sensitive to humidity conditions because high- and low-hydration phases were interconvertible at a critical humidity of 10%, 20%, and 50%, respectively, as supported by both X-ray diffraction and gravimetry as a function of the relative humidity. In the phase conversion process, interlayer expansion or contraction of approximately 0.2 A also occurred as a possible consequence of absorption/desorption of H(2)O molecules. The hydration difference was also evidenced by refinement results. The number of coordinated water molecules per formula weight, n, changed from 6.6 for the high-hydration Gd sample to 6.0 for the low-hydration Gd sample. Also, the hydration number usually decreased with increasing atomic number; e.g., n = 7.4, 6.3, 7.2, and 6.6 for high-hydration Nd, Sm, Eu, and Gd, and n = 6.0, 5.8, 5.6, 5.4, and 4.9 for low-hydration Gd, Tb, Dy, Ho, and Er. The variation in the average Ln-O bond length with decreasing size of the lanthanide ions is also discussed. This family of layered lanthanide compounds highlights a novel chemistry of interplay between crystal structure stability and coordination geometry with water molecules.     

Synthesis, potentiometric, kinetic, and NMR Studies of 1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid)-4,10-bis(methylenephosphonic acid) (DO2A2P) and its complexes with Ca(II), Cu(II), Zn(II) and lanthanide(III) ions

A cyclen-based ligand containing trans-acetate and trans-methylenephosphonate pendant groups, H 6DO2A2P, was synthesized and its protonation constants (12.6, 11.43, 5.95, 6.15, 2.88, and 2.77) were determined by pH-potentiometry and (1)H NMR spectroscopy. The first two protonations were shown to occur at the two macrocyclic ring N-CH 2-PO 3 (2-) nitrogens while the third and fourth protonations occur at the two phosphonate groups. In parallel with protonation of the two -PO 3 (2-) groups, the protons from the NH (+)-CH 2-PO 3 (2-) are transferred to the N-CH 2-COO (-) nitrogens. The stability constants of the Ca (2+), Cu (2+), and Zn (2+) (ML, MHL, MH 2L, and M 2L) complexes were determined by direct pH-potentiometry. Lanthanide(III) ions (Ln (3+)) form similar species, but the formation of complexes is slow; so, "out-of-cell" pH-potentiometry (La (3+), Eu (3+), Gd (3+), Y (3+)) and competitive spectrophotometry with Cu(II) ion (Lu (3+)) were used to determine the stability constants. By comparing the log K ML values with those of the corresponding DOTA (H 4DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and DOTP (H 8DOTP = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethylenephosphonic acid) complexes, the order DOTA < DO2A2P < DOTP was found for all the metal ion complexes examined here with the exception of the Ca (2+) complexes, for which the order is reversed. The relaxivity of Gd(DO2A2P) decreases between pH 2 and 7 but remains constant in the pH range of 7 < pH < 12 ( r 1 = 3.6 mM (-1) s (-1)). The linewiths of the (17)O NMR signals of water in the absence and presence of Gd(DO2A2P) (at pH = 3.45 and 8.5) between 274 and 350 K are practically the same, characteristic of a q = 0 complex. Detailed kinetic studies of the Ce (3+) and Gd (3+) complexes with DO2A2P showed that complex formation is slow and involves a high stability diprotonated intermediate Ln(H 2DO2A2P)*. Rearrangement of the diprotonated intermediate into the final complex is an OH (-) assisted process but, unlike formation of Ln(DOTA) complexes, rearrangement of Ln(H 2DO2A2P)* also takes place spontaneously likely as a result of transfer of one of the protons from a ring nitrogen to a phosphonate group. The order of the OH (-) assisted formation rates of complexes is DOTA > DO2A2P > DOTP while the order of the proton assisted dissociation rates of the Gd (3+) complexes is reversed, DOTP > DO2A2P > DOTA. (1)H and (13)C NMR spectra of Eu(DO2A2P) and Lu(DO2A2P) were assigned using two-dimensional correlation spectroscopy (2D COSY), heteronuclear multiple quantum coherence (HMQC), heteronuclear chemical shift correlation (HETCOR), and exchange spectroscopy (EXSY) NMR methods. Two sets of (1)H NMR signals were observed for Eu(DO2A2P) characteristic of the presence of two coordination isomers in solution, a twisted square antiprism (TSAP) and a square antiprism (SAP), in the ratio of ~93% and ~7%, respectively. Line shape analysis of the (1)H NMR spectra of Lu(DO2A2P) gave lower activation parameters compared to La(DOTP) for interconversion between coordination isomers. This indicates that the Ln(DO2A2P) complexes are less rigid probably due to the different size and spatial requirements of the carboxylate and phosphonate groups.     

Novel heterometal-organic complexes as first single source precursors for up-converting NaY(Ln)F4 (Ln = Yb, Er, Tm) nanomaterials

First heterometal-organic single source precursors for NaYF(4) nanomaterials as a host matrix for up-conversion emission are reported. These novel heterobimetallic derivatives NaY(TFA)(4)(diglyme) (1), [Na(triglyme)(2)][Y(2)(TFA)(7)(THF)(2)] (2) and Na(2)Y(TFA)(5)(tetraglyme) (3) (TFA = trifluoroacetate), which were fully characterized by elemental analysis, FT-IR and (1)H NMR spectroscopy, TG-DTA data as well as single crystal X-ray structures, are advantageous in terms of being anhydrous and having lower decomposition temperatures in comparison to the homometallic precursor Y(TFA)(3)(H(2)O)(3). In addition, they also contain chelating glyme ligands, which act as capping reagents during decomposition to control the NaYF(4) particle size and render them monodisperse in organic solvents. On decomposition in 1-octadecene, the molecular derivatives 1 and 3 are converted, in the absence of any surfactant or capping reagent, to cubic NaYF(4) nanocrystals at significantly lower temperatures (below 250 °C). At higher temperature, a mixture of the cubic and hexagonal phases was obtained, the relative ratio of the two phases depending on the reaction temperature. A pure hexagonal phase, which is many folds more efficient for UC emission than the cubic phase, was obtained by calcining nanocrystals of mixed phase at 400 °C. In order to co-dope this host matrix with up-converting lanthanide cations, analogous complexes NaLn(TFA)(4)(diglyme) [Ln = Er (4), Tm (5), Yb (6)] and Na(2)Ln(TFA)(5)(tetraglyme) [Ln = Er (7), Yb (8)] were also prepared and characterized. The decomposition in 1-octadecene of suitable combinations and appropriate molar ratios of these yttrium, ytterbium and erbium/thulium derivatives gave cubic and/or hexagonal NaYF(4): Yb(3+), Er(3+)/Tm(3+) nanocrystals (NCs) capped by diglyme or tetraglyme ligands, which were characterized by IR, TG-DTA data, EDX analysis and TEM studies. Surface modification of these NCs by ligand exchange reactions with poly acrylic acid (PAA) and polyethyleneglycol (PEG) diacid 600 was also carried out to render them water soluble. The THF solutions of suitable combinations of the diglyme derivatives were also used to elaborate the thin films of NaYF(4):Yb(3+), Er(3+)/Tm(3+) on a glass or Si wafer substrate by spin coating. The multicolour up-conversion fluorescence was successfully realized in the Yb(3+)/Er(3+) (green/red) and Yb(3+)/Tm(3+) (blue/violet) co-doped NaYF(4) nanoparticles and thin films, which demonstrates that they are promising UC nanophosphors of immense practical interest. The up-conversion excitation pathways for the Er(3+)/Yb(3+) and Tm(3+)/Yb(3+) co-doped materials are discussed.     

Near-infrared luminescent hybrid materials doped with lanthanide (Ln) complexes (Ln = Nd, Yb) and their possible laser application

The crystal structures of ternary Ln(DBM)(3)phen complexes (DBM = dibenzoylmethane, phen = 1,10-phenanthroline, and Ln = Nd, Yb) and their in situ syntheses via the sol-gel process are reported. The properties of the Ln(DBM)(3)phen complexes and their corresponding Ln(3+)/DBM/phen-co-doped luminescent hybrid gels obtained via an in situ method (Ln-D-P gel) have been studied. The results reveal that the lanthanide complexes are successfully in situ synthesized in the corresponding Ln-D-P gels. Both Ln(DBM)(3)phen complexes and Ln-D-P gels display sensitized near-infrared (NIR) luminescence upon excitation at the maximum absorption of the ligands, which contributes to the efficient energy transfer from the ligands to the Ln(3+) ions (Ln = Nd, Yb), an antenna effect. The radiative properties of the Nd(3+) ion in a Nd-D-P gel are discussed using Judd-Ofelt analysis, which indicates that the (4)F(3/2) --> (4)I(11/2) transition of the Nd(3+) ion in the Nd-D-P gel can be considered as a possible laser transition.     

Synthesis and characterization of copper-, zinc-, manganese-, and cobalt-substituted dimeric heteropolyanions, [(alpha-XW9O33)2M3(H2O)3](n-) (n = 12, X =As(III), Sb(III), M = Cu(2+), Zn(2+); n = 10, X = Se(IV), Te(IV), M = Cu(2+) and [(alpha-AsW9O33)2WO(H2O)M2(H2O)2](10-) (M = Zn(2+), Mn(2+), Co(2+)

Interaction of the lacunary [alpha-XW9O33](9-) (X = As(III), Sb(III)) with Cu(2+) and Zn(2+) ions in neutral, aqueous medium leads to the formation of dimeric polyoxoanions, [(alpha-XW9O33)2M3(H2O)3](12-) (M = Cu(2+), Zn(2+); X = As(III), Sb(III)), in high yield. The selenium and tellurium analogues of the copper-containing heteropolyanions are also reported: [(alpha-XW9O33)2Cu3(H2O)3](10-) (X = Se(IV), Te(IV)). The polyanions consist of two [alpha-XW9O33] units joined by three equivalent Cu(2+) (X = As, Sb, Se, Te) or Zn(2+) (X = As, Sb) ions. All copper and zinc ions have one terminal water molecule resulting in square-pyramidal coordination geometry. Therefore, the title anions have idealized D3h symmetry. The space between the three transition metal ions is occupied by three sodium ions (M = Cu(2+), Zn(2+); X = As(III), Sb(III)) or potassium ions (M = Cu(2+); X = Se(IV), Te(IV)) leading to a central belt of six metal atoms alternating in position. Reaction of [alpha-AsW9O33](9-) with Zn(2+), Co(2+), and Mn(2+) ions in acidic medium (pH = 4-5) results in the same structural type but with a lower degree of transition-metal substitution, [(alpha-AsW9O33)2WO(H2O)M2(H2O)2](10-) (M = Zn(2+), Co(2+), Mn(2+)). All nine compounds are characterized by single-crystal X-ray diffraction, IR spectroscopy, and elemental analysis. The solution properties of [(alpha-XW9O33)2Zn3(H2O)3](12-) (X = As(III), Sb(III)) were also studied by 183W-NMR spectroscopy.