Rafal J. Wiglusz

Precursor and solvent effects in the nonhydrolytic synthesis of complex oxide nanoparticles for bioimaging applications by the ether elimination (Bradley) reaction.

Investigation of the solvent and alkoxide precursor effect on the nonhydrolytic sol-gel synthesis of oxide nanoparticles by means of an ether elimination (Bradley) reaction indicates that the best crystallinity of the resulting oxide particles is achieved on application of aprotic ketone solvents, such as acetophenone, and of smallest possible alkoxide groups. The size of the produced primary particles is always about 5 nm caused by intrinsic mechanisms of their formation. The produced particles, possessing the composition of natural highly insoluble minerals, are biocompatible. Optical characteristics of the perovskite complex oxide nanoparticles can easily be controlled through doping with rare earth cations; for example, by Eu(3+). They can be targeted through surface modification by anchoring the directing biomolecules through a phosphate or phosphonate moiety. Testing of the distribution of Eu-doped BaTiO(3) particles, modified with ethylphosphonic acid, demonstrates their facile uptake by the plants with active fluid transport, resulting finally in their enhanced concentration within the cell membranes.

Facile non-hydrolytic synthesis of highly water dispersible, surfactant free nanoparticles of synthetic MFe2O4 (M–Mn2+, Fe2+, Co2+, Ni2+) ferrite spinel by a modified Bradley reaction

A series of the highly crystalline MFe2O4 ferrite spinel nanoparticles were synthesized via a modified Bradley reaction using microwave stimulation. Particle size was estimated using theoretical calculations from the X-ray data (Scherrer and Rietveld methods) as well as by direct experimental techniques such as TEM, DLS and NTA. The calculated average grain size for dry powders is in the range 10 to 23 nm. Hydrodynamic size was measured using DLS on non-modified, surfactant free particles of the whole MFe2O4 series. Raman spectra used for additional verification of the structure features of the produced spinel phases showed strong asymmetric behavior of the A1g mode, which was deconvoluted revealing additional components. Among all the products the lowest site inversion was found for the manganese ferrite (MnFe2O4). The oxidation of Fe3O4 leading to the formation of the Fe2O3 hematite phase induced by laser irradiation was observed. Magnetic characterization of the MFe2O4 family was carried out, showing that superparamagnetic blocking temperatures and calculated anisotropy constants K are in good agreement with the data for similar fine-particle systems.

Synthesis, Structure, and Optical Properties of LiEu(PO3)4 Nanoparticles

A wet chemical approach was employed for the preparation of LiEu(PO(3))(4) nanoparticles. XRD, Raman spectroscopy, TEM, SAED, and IR measurements were used in order to determine the crystal structure and morphology of the obtained product. Complete optical studies including absorption, excitation, emission, and kinetic measurements were performed. At least two components of the (5)D(0) → (7)F(0) transition were found, indicating the existence of more than one crystallographic position of the Eu(3+) ions. Asymmetry parameter R as well as the covalence of the Eu-O bond were found to decrease with the grain growth.

Correlation between spectroscopic characteristics and structure of lanthanide phosphoro-azo derivatives of β-diketones

Two types of lanthanide (Nd, Eu, Pr) compounds of formulae: Ln(HX) 3 Cl 3 (1), Ln(HX) 3 (NO 3 ) 3 (2) [where HX=CCl 3 CO-NH-PO(NEt 2 ) 2 ] with the same ligand type but with different coordination numbers (as a consequence of different site symmetries) were obtained. X-ray data indicate the formation of octahedral complexes of (1), strongly distorted into trigonal symmetry, the strongest distortion observed for europium single crystals. On the other hand, the second type of crystals creates intermediate coordination polyhedra with low symmetry; anisotropy of intensities of 4 I 9/2 → 4 G 5/2 , 2 G 7/2 transition of Nd crystal well confirms the above structure. High resolution absorption spectra of single crystals of the title compounds were recorded at different temperatures from 293 to 4.2 K. Splitting of levels was determined. Intensities of f-f transitions were calculated and changes of their oscillator strengths, in the region of hypersensitive transitions, for the series Pr, Nd, Eu crystals were related to stronger distortion of the symmetry with a decrease of the ionic radius. Oscillator strength values and Judd-Ofelt parameters were calculated and compared to the respective data reported earlier. Analysis of the electronic components in low temperature spectra point on the D 3 site in (1) and most probably C 2v in (2). Electron-phonon coupling was observed in low temperature spectra and its probabilities was analysed for two types of compounds with different symmetries. Vibronic components were related to the internal ligand modes and to the localised Ln-L x modes.

Role of the Sintering Temperature and Doping Level in the Structural and Spectral Properties of Eu-Doped Nanocrystalline YVO4

A sol-gel approach was employed to prepare nanosized YVO(4) nanopowders doped with Eu(3+) ions. Raw nanomaterials were thermally treated at 700-1000 °C for 3 h. X-ray diffraction (XRD) analysis demonstrated that single-phase nanopowders with high crystallite dispersion were obtained. Our studies were focused on relating the luminescence properties of the Eu(3+) dopant to the nanocrystallite (NC) size. Depending on the thermal treatment, the average NC size was calculated to range from 20 nm to 1.1 μm. We have found that the size effect manifests mainly in the expansion of the cell volume and broadening of XRD peaks, as indicated by Rietveld analysis. Moreover, emission and excitation spectra, although typical for the Eu(3+) ions, demonstrated some degree of correlation with the calcination temperature and doping concentration. To explain these differences a detailed analysis of the luminescence spectra by the Judd-Ofelt theory has been performed.

Crystal Structure and Morphology Evolution in the LaXO3, X = Al, Ga, In Nano-Oxide Series. Consequences for the Synthesis of Luminescent Phosphors

The LaXO(3):Tb(3+) (X = Al(3+), Ga(3+), In(3+)) perovskite nanoparticles were obtained using the nonhydrolytic treatment (Bradley reaction) of the molecular precursors of the La(O(i)Pr)(3), Al(O(i)Pr)(3), Ga(O(i)Pr)(3), In(5)O(O(i)Pr)(13), and Tb(acac)(3), respectively. It was shown that crystal structure and morphology evolution in the LaXO(3), X = Al, Ga, In nano-oxide series depended on the size and chemical properties of the X-metal atom. Formation of the LaInO(3):Tb(3+) nanoparticles is distinctly less thermodynamically demanding on contrary to the LaAlO(3):Tb(3+) and LaGaO(3):Tb(3+) since it provided crystalline product directly in the solution synthesis at 202 °C, which is the lowest reported synthesis temperature for this compound up-to-date. This behavior was ascribed to the effects directly connected with the dopant substitution (exchange of bigger La(3+) cation with smaller Tb(3+)) as well as reduction of the particle size. The size effects are mostly reflected in the expansion of the cell volume, changes of the cell parameters as well as shifting and broadening of the Raman bands. Indirectly, size reduction has also an effect on the luminescence properties through the higher probability of presence of surface and net defects as well as heterogeneous distribution of the Tb(3+) ions caused by high surface-to-volume ratio. The prepared nanophosphors show basically green emission with exception of white-green in case of the LaInO(3):Tb(3+). Strong emission quenching was found in the latter case being most likely a consequence of the nonradiative energy transfer between Tb(3+) and In(3+) as well as the presence of defects. In comparison to the Pechinis method, the LaXO(3) nanoparticles required significantly lower annealing temperature (700 °C) necessary for complete crystallization. Generally the resulting particles are distinctly smaller (5 to 25 nm) and less agglomerated (50-100 nm) depending on the reaction conditions as well as thermal treatment. For the first time, it was shown that the LaGaO(3):Tb(3+) nanopowder has crystallized in the high-temperature rhombohedral R3c phase.

Lanthanum molybdate nanoparticles from the Bradley reaction: factors influencing their composition, structure, and functional characteristics as potential matrixes for luminescent phosphors.

Interaction of lanthanum isopropoxide with molybdenum(VI) alkoxides in La/Mo ratios varying from 3:1 to 1:1 in acetophenon or allyl alcohol as solvents offers nanosized poorly crystalline products of complex composition, where the precipitation of Mo-rich ones is followed by the formation of La-rich ones with conservation of the reaction stoichiometry in total. Thermal treatment of the precipitates at temperatures over 700 °C leads to the formation of stoichiometric phases of the α- and β-La2Mo2O9 compositions. Introduction of smaller Re3+ cations such as Sm3+ by doping favors stabilization of the La2–xRExMo2O9 phase with improved crystallinity even after lower-temperature thermal treatment. The doping is successful only when the Re3+ (Sm3+, Eu3+, and Tb3+) is introduced as an alkoxide: application of Re3+(acac)3 as Re3+ sources leads to materials free from Re3+. The produced samples were characterized by XPD, TGA, SEM, and TEM studies as well as the luminescent properties for the Sm3+-doped phases.

Synthesis and spectroscopic characteristics of a new class of lanthanide compounds of formulae Ln(HX)3(NO3)3 and Ln(HX)3Cl3

Two series of the lanthanide (Eu, Pr) compounds of the formulae Ln(HX)3Cl3 (1); Ln(HX)3(NO3)3 (2) [where HX=CCl3CO–NH–PO(NEt2)2] with C.N.=6 and 9 were obtained in the form of monocrystals. The spectroscopic properties of these compounds were investigated at 293, 77 and 4.2 K and the results related to their structures. Correlation was made with the spectroscopic data and structure of the Eu and Nd respective chelates. Essential differences were found in coordination mode of ligand molecules in those systems. Intensity analysis of electronic transitions, electron–phonon coupling, as well as splitting and energies of electronic levels were used as tests of metal bonding in the systems under investigation. The electronic f–f transitions of praseodymium (1, 2) compounds show drastic differences in oscillator strength values, pointing thus at substantial differences in symmetry of the metal centre. Judd–Ofelt parameters were calculated with low errors of estimation. The relatively strong vibronic lines appear at displacement frequencies, corresponding to both ligand and Ln–Ln localised vibrational modes.

Preferential site substitution of Eu3+ ions in Ca10(PO4)6Cl2 nanoparticles obtained using a microwave stimulated wet chemistry technique

The Eu3+ doped Ca10(PO4)6Cl2 nanocrystalline powders were synthesized using a microwave stimulated technique. Additional post heat treatment in the temperature range 800–1100 °C was applied in order to improve the crystallinity of the final product and eliminate the residual amorphous phase. Detailed structural characterization was performed by X-ray diffraction (XRD), Raman and infrared (IR) spectroscopy, transmission electron microscopy (TEM) and X-ray fluorescence (EDX). The optical properties of the Ca10(PO4)6Cl2 samples doped with different Eu3+ concentrations (0.5–5 mol%) were determined by measuring excitation, emission spectra and luminescence. TEM images confirmed the nanoscale nature of the final product with a primary particle size of about 60 nm and a hydrodynamic size of 200 nm when the product was dispersed in Milli-Q purified water (MQ) without further stabilization. The analysis of the 5D0 → 7F0 transition points out that for low concentration Ca(II) (A) site is preferentially substituted whereas increase of Eu3+ above 2 mol% results in domination of the Eu3+ cations located at Ca(I) (B) site. Increase of annealing temperature leads to an increase of the 5D0 → 7F0 intensity associated with the Eu3+ at A site. Preferential site substitution can be solved by analysis of the optical properties of the Eu3+ ion. The Judd–Ofelt parameters were calculated using simplified formalisms. The mechanism of concentration quenching process was identified as a dipole–dipole interaction.

Effect of lithium substitution on the charge compensation, structural and luminescence properties of nanocrystalline Ca10(PO4)6F2 activated with Eu3+ ions

Eu3+ and Li+ ion co-doped fluorapatite (Ca10(PO4)6F2) nanocrystals were fabricated using a microwave stimulated hydrothermal technique followed by heat treatment at 500 °C. The concentration of Eu3+ ions was set to be 1 mol% and that of the Li+ ions was in the range of 0.5–5 mol% to investigate the site occupancy preference and charge compensation co-doping. The structural and morphological properties of the obtained samples were determined by using XRD (X-ray powder diffraction) and TEM (transmission electron microscopy) techniques as well as IR (infrared) and micro-Raman spectroscopy. The particle size was verified and calculated by the Rietveld method being in the range of 70–95 nm. The luminescence properties (the emission, excitation spectra and emission kinetics) of the Eu3+ ion-doped fluorapatite depending on the co-dopant (Li+ ions) were recorded. Significantly, fluorescence quenching by OH− groups was eliminated by F- ions and the luminescence intensity was enhanced by co-doping with Li+ ions. The simplified Judd–Ofelt (J–O) theory has been performed to explain a detailed analysis of the luminescence spectra.