Pechini-type Sol Gel Method Research Articles

Optical investigation of Tb3+-doped Y2O3 nanocrystals prepared by Pechini-type sol–gel process

We report an optical study of Tb3+-doped Y2O3 nanocrystals synthesized by Pechini-type sol–gel method. The particles are investigated in terms of size and morphology by means of X-ray diffraction and transmission electron microscopy analysis. It is shown how the simple Pechini method allows for the growth of monocrystalline nanoparticles with a volume-weighted average size of about 30 nm. The optical properties of Tb3+ in the host lattice are studied in terms of PL, PLE, and lifetimes. Moreover, a correlation between the type of decay curves, the emission and excitation bands' shapes, and the site location of the emitting Tb3+ in the host material Y2O3 is proposed.

Effect of Fe addition on phase transformation of titanium dioxide nanocrystals prepared by Pechini-type sol–gel method

In the current work, titanium dioxide and iron-doped titanium dioxide (0-3-) nanocrystals were prepared with the Pechini-type sol-gel method. The same procedure as well as spin-coating technique was applied for preparation of thin films. The prepared samples were characterised by X-ray diffractometery (XRD) and X-ray photoelectron spectroscopy techniques. The crystallographic and microstructural parameters of nanopowders were refined from XRD patterns utilising the Rietveld refinement method. It was found that with incorporation of iron in TiO 2 structure, a highly distorted brookite phase was generated and the amount of anatase phase was decreased. The rutile phase disappeared with addition of iron; however, in higher concentration of iron (3%), it reappeared. The results also indicate that the crystallite size of brookite phase as well as microstrain of anatase and brookite phases were amplified with iron doping. The results of the photocatalytic test of prepared thin films are in agreement with the prediction of photocatalytic activity of samples based on their phase%s constituents and structure.

Green/green-yellow-emitting KSrGd(PO4)2:Ce3+, Tb3+/Mn2+ phosphors with high quantum efficiency for LEDs and FEDs

Ce(3+), Tb(3+) and Mn(2+)-activated KSrGd(PO(4))(2) phosphors with high absolute quantum efficiencies were first prepared by a Pechini-type sol-gel method. The photoluminescence and cathodoluminescence intensities of Tb(3+)/Mn(2+) can be enhanced by co-doped Ce(3+) ions into the KSrGd(PO(4))(2) host via the energy transfer process.

Nanocrystalline CaYAlO4:Tb3+/Eu3+ as promising phosphors for full-color field emission displays

Eu(3+) and/or Tb(3+)-doped CaYAlO(4) phosphor samples were synthesized by Pechini-type sol-gel method. X-Ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), photoluminescence (PL) and cathodoluminescence (CL) spectra were used to characterize the samples. For CaYAlO(4):Tb(3+), it is shown that the Tb(3+)-doping concentration has a significant effect on the (5)D(3)/(5)D(4) emission intensity of Tb(3+), which is attributed to the cross relaxation from (5)D(3) to (5)D(4). Under the 4f(8)→ 4f(7)5d excitation of Tb(3+) or low-voltage electron beams excitation, the CaYAlO(4):Tb(3+) phosphors show tunable luminescence from blue to cyan, and then to green with the change of Tb(3+)-doping concentration. The CaYAlO(4):Eu(3+) samples exhibit a reddish-orange emission of Eu(3+) corresponding to (5)D(0,1)→(7)F(0,1,2,3) transitions. Furthermore, a white emission can be realized in the single phase CaYAlO(4) host by reasonably adjusting the doping concentrations of Tb(3+) and Eu(3+) under low-voltage electron beams excitation. Compared with the commercial blue (Y(2)SiO(5):Ce(3+)) and green (ZnO:Zn) phosphors, CaYAlO(4):0.1%Tb(3+) and CaYAlO(4):5%Tb(3+) phosphors have higher CL intensity and stability under continuous electron bombardment. Due to the excellent CL properties and good CIE chromaticity coordinates, the as-prepared Tb(3+)/Eu(3+)-doped CaYAlO(4) nanocrystalline phosphors have potential application in FEDs devices.

Porous MAl 2O 4:Eu 2+ (Eu 3+), Dy 3+ (M = Sr, Ca, Ba) phosphors prepared by Pechini-type sol–gel method: The effect of solvents

In this work, a series of porous Eu 2+-doped alkaline earth aluminates phosphors including MAl 2O 4:Eu 2+ (Eu 3+), Dy 3+ (M = Sr, Ca, Ba) have been prepared by Pechini-type sol–gel approach, using citric acid as chelating ligand and ethylene glycol (or H 2O) as solvent. The as-obtained samples were characterized by means of XRPD, FESEM and PL techniques. MAl 2O 4:Eu 2+, Dy 3+ (M = Sr, Ca, Ba) phosphors were prepared in a reducing atmosphere (H 2/Ar, 20 + 80%) while MAl 2O 4:Eu 3+, Dy 3+ (M = Sr, Ca, Ba) phosphors were obtained in air. Upon changing the molar ratio of citric acid to total metal cations concentration in ethylene glycol can produce spherical phosphors and the higher molar ratio favors the formation of spherical ones. Otherwise, irregular shaped phosphors occur when conducting the reaction in pure H 2O. The irregular shaped phosphors have higher emission intensity than those spherical ones observed with the help of excitation spectra, emission spectra and decay curves.

Enhanced Stokes and Anti-Stokes Photoluminescence Emission from LaAlO<SUB>3</SUB>:Nd<SUP>+3</SUP> Nanosized Powder Coated with a SiO<SUB>2</SUB> Shell Layer

The research on and development of materials in the field of rare-earth-ion doped nanocrystals for downconversion and up-conversion emission has been recognized to hold tremendous potential in the areas of photonic and biophotonic applications. In the present manuscript, the comprehensive results of the investigation of Stokes and anti-Stokes photoluminescence emission from the prepared LaAlO3:Nd+3 nanoparticles synthesized via the Pechini-type sol-gel method are presented and explained. The XRD diffraction peaks of the LaAlO3:Nd+3 nanoparticles can be easily assigned to the cubic-perovskite LaAlO3 structure. The FESEM image confirms the formation of approximately spherical particles within the range of 80 +/- 30 nm. The PL results showed that the LaAlO3 doped with 5% of Nd+3 ions shows the strongest emission. The core-shell structures obviously enhanced the photoluminescence intensity by suppressing the non-radiative emission and surface defects. As they yield the best PL measurement results, the LaAlO3:0.05Nd+3 nanoparticles were coated with a SiO2 shell layer, to enhance the photoluminescence emission. The mechanisms that are responsible for the photoluminescence emission process observed in the samples are discussed herein, with the help of the Nd+3 ion Dieke energy level diagram. Power dependence slope measurements were performed to identify the processes involved in the LaAlO3:Nd+3 up-conversion photoluminescence.

Rattle-type hollow CaWO4:Tb3+@SiO2 nanocapsules as carriers for drug delivery

Rattle-type hollow nanocapsules are among of the most promising candidates as drug carriers owing to their huge inner space and multifunctional material combination. In this paper, rattle-type hollow CaWO(4):Tb(3+)@SiO(2) nanocapsules with a diameter of 100-110 nm and a wall thickness around 10 nm were fabricated. The hollow silica nanospheres were used as nano-reactors and the luminescent core of CaWO(4):Tb(3+) was post-filled into the nano-reactors by a vacuum nano-casting route combined with a Pechini-type sol-gel method. Subsequently, doxorubicin hydrochloride (DOX), a model of an anti-cancer drug, is loaded into the CaWO(4):Tb(3+)@SiO(2) nanocapsules and their cell cytotoxicity, cancer cell uptake and drug release behavior are investigated in vitro. The prepared multifunctional inorganic nanocapsules show a loading capacity for DOX as high as 124 mg g(-1) and sustained-release properties. The release profile of the drug from DOX-loaded nanocapsules can last over five days. Besides, the blank CaWO(4):Tb(3+)@SiO(2) shows very low cytotoxicity against cancer cell lines (HeLa cell) while the DOX-loaded nanocapsules exhibit relatively high efficiency for killing of HeLa cells. The rapid cancer cell uptake process is observed by confocal laser scanning microscopy. The results indicate that a rattle-type hollow CaWO(4):Tb(3+)@SiO(2) nanocapsule has the potential to be used as drug carrier in therapy. Moreover, it is possible to extend the synthetic strategy in this study to other rattle-type multifunctional composites to meet various demands.

Site-Occupation and Crystal-Field Splitting of Eu3+ in BaY2O4 with Calcium-Ferrite Structure

Luminescence properties of BaY2O4:Eu3+ are investigated by the site-selective laser-excitation spectroscopy in the temperature region 15–300 K. The phosphors were synthesized by the Pechini-type sol-gel method for different Eu3+-concentrations. Three different crystallographic sites corresponding to two Y3+ sites (Y1 and Y2) and the Ba site for Eu3+ are identified from the excitation spectra due to the 7F0 → 5D0 transition. Crystal-field splittings of the 7F1 and 7F2 multiplets lead to classify three different sites for Eu3+ in BaY2O4 lattice. Luminescence decays and spectral features at each site depend strongly on temperature and Eu3+-concentration in BaY2O4:Eu3+.

Effect of Eu 3+ contents on the structure and properties of BaLa 2ZnO 5:Eu 3+ phosphors

A series of Eu 3+ doped BaLa 2ZnO 5 was prepared by a Pechini-type sol–gel method. The effect of Eu 3+ concentration on the structure and the luminescent properties of the samples BaLa 2− x Eu x ZnO 5 were investigated by powder X-ray diffraction (XRD) and photoluminescence (PL) spectra. The sample adopts the tetragonal or orthorhombic structure as the Eu 3+ concentration reaches below 1.2 or over 1.6, respectively. The sample is a mixture of tetragonal and orthorhombic phases as the contents of dopants lie between 1.2 and 1.6. The phosphor offers the strongest red light as content of Eu 3+ is 0.4. In addition, the crystallization processes of the complex precursors were examined by simultaneous thermogravimetry and differential thermal analysis (TG–DTA), and also the optimal heating temperature was investigated.

Visible upconversion luminescence of Tb 3+ ions in Y 2O 3 nanoparticles induced by a near-infrared femtosecond laser

Y 2O 3:Tb 3+ nanoparticles were synthesized using Pechini-type sol–gel method, and characterized by TEM, XRD, and Raman spectra. Their spectroscopic properties are investigated using optical absorption, spectral- and time-resolved upconversion emission spectra. The dependence of Tb 3+ emission intensity on pump power density reveals that it is a three-photon excitation process. These results above indicate that upconversion excitation practically originates from the parity-allowed 4 f–5 d transition via a three-photon simultaneous absorption of Tb 3+ ions. The upconversion luminescence intensities of Y 2O 3:Tb 3+ nanoparticles decrease with Tb 3+ doping concentrations in the range of 1∼4 mol%. The measured average lifetimes of the 5D 4 level of Tb 3+ ions also decrease with increasing Tb 3+ concentrations at room temperature.

Fabrication and optical properties of NUV-emitting SiO 2–SrB 4O 7:Eu 2+ glass–ceramic thin films

SiO 2–SrB 4O 7:Eu 2+ glass–ceramic thin films were fabricated for possible application in near ultraviolet (NUV) emitting devices. Nano-sized SrB 4O 7:Eu 2+ powders were prepared by a Pechini-type sol–gel method and a subsequent ball-milling treatment. The powders showed NUV emissions centered at 367 nm, upon irradiation with UV of shorter wavelengths, due to an allowed 4 f 65 d 1 → 4 f 7 electronic transition of Eu 2+ ions. The glass–ceramic thin films were prepared by dip-coating of tetraethylorthosilicate (TEOS) solutions dispersed with the nano-sized SrB 4O 7:Eu 2+ powders and a subsequent heat-treatment. It was found that the glass–ceramic thin films had relatively high thermal stability up to 800 °C in terms of the Eu 2+ emissions. SiO 2 layers surrounding SrB 4O 7:Eu 2+ appeared to be effective for the surface passivation of the phosphor particles.

Synthesis and Characterization of Monodispersed SiO2@Y3Al5O12:Er3+ Core-Shell Particles

Submicron core-shell structure particles SiO2@Y3Al5O12:Er3+, which silica spherical particles was coated with an yttrium aluminum garnet (Y3Al5O12) layer doped with Er3+, were prepared by the modified Pechini-Type sol-gel method for the first time. The structure and morphology of samples were detected by the X-ray powder diffraction (XRD) measurement, field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), respectively. The results indicate that well-crystallized garnet nanocrystallines were formed on the surface of the silica particles. The luminescent spectra in near infrared and visible region of the core-shell structured SiO2@Y3Al5O12:Er3+ powders were also investigated and compared with those of the pure Y3Al5O12:Er3+ and the Er3+ doped silicate glass. The results show that mono-dispersed SiO2@Y3Al5O12:Er3+ core-shell spherical particles with the near infrared, red and green luminescent emissions under the excitation of 980 nm laser diode have been successfully synthesized.

Silica-/titania-coated Y2O3:Tm3+, Yb3+ nanoparticles with improvement in upconversion luminescence induced by different thickness shells

In order to improve the upconversion (UC) luminescence of lanthanide-doped nanoparticles (NPs), different sized Y2O3:Tm3+, Yb3+ NPs were synthesized using the Pechini type sol-gel method, and their surfaces were coated with different thickness of SiO2 or TiO2 shells using the Stöber method. The results indicate that large-sized NPs have more intense UC luminescence intensities than small-sized NPs. The core-shell structures can enhance the UC luminescence intensities. Comparing with the UC luminescence intensity of noncoated NPs, the UC luminescence intensities of SiO2-coated NPs for the sintering time of 60 min and the coating time of 30, 60, 90, and 120 min are enhanced by 1.53, 1.54, 1.40, and 1.16 times, respectively. According to the relative variable ratios of the UC luminescence intensities, a competition process between two mechanisms was proposed to explain the effects of different thickness shells and different shell materials on the UC luminescence intensities. One mechanism is the role conversion of lanthanide ions on the NPs’ surfaces, which is from the “dormant” state to the “activated” state due to the complementary ligand fields from noncrystalline SiO2 shells. The other is the absorption effects of the shells on the incident pump light and the reabsorption effects of the shells on the UC luminescence. Therefore, it can be concluded that more intense UC luminescence can be achieved in doped core-shell NPs by selecting the appropriate shell materials and their thickness.

The two-photon excitation of SiO2-coated Y2O3:Eu3+ nanoparticles by a near-infrared femtosecond laser

In order to improve the photoluminescence property ofEu3+-dopednanoparticles, Y2O3:Eu3+ nanoparticles were synthesized using the Pechini-type sol–gel method, then coated withSiO2 shells by using the Stöber method for different coating times. TheSiO2-coated nanoparticles were characterized by x-ray diffraction (XRD), transmission electronmicroscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy and Ramanspectroscopy, and their photoluminescence spectra were recorded under 800 nm femtosecondlaser excitation. The results indicate that a two-photon simultaneous absorptionupconversion luminescence is obtained, and their upconversion luminescence intensities arefurther enhanced after the surfaces of the nanoparticles are coated with different thicknessSiO2 shells. Compared to the upconversion luminescence intensity of non-coatednanoparticles at 611 nm, the upconversion luminescence intensities ofSiO2-coatedY2O3:Eu3+ nanoparticles with coating times of 60, 90 and 120 min were enhanced by 3.30, 3.96 and 4.13times, respectively. This can be attributed to the contributions of the increased amounts ofEu3+ ions populatedat the 5D0 level on the surfaces of the nanoparticles because the cooperative ligand fields between theY2O3 core and non-crystallineSiO2 shell interfacesactivate the ‘dormant’ Eu3+ ions near or on the surfaces of the nanoparticles. From a Judd–Ofelt (J–O) theoryanalysis, the coated shell structures can improve the radiative quantum efficiencies ofEu3+-doped nanoparticles. It is therefore concluded that more intense red upconversionluminescence with high radiative quantum efficiencies can enable theSiO2-coatedY2O3:Eu3+ nanoparticles to have the great potential to be used as a fine resolution phosphor.

Experimental study on the surface modification ofY2O3:Tm3+/Yb3+ nanoparticles to enhance upconversion fluorescence and weaken aggregation

In order to improve the solubility of doped nanoparticles in solutions,Y2O3:Tm3+/Yb3+ nanoparticles were synthesized using the Pechini-type sol–gel method, and their surfaces weremodified with amino or carboxylic functional groups using ligand-capped and ligand-exchangingmethods. The nanoparticles with modified surfaces were characterized by transmission electronmicroscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy and zeta potential(ζ), and their photoluminescence was studied by fluorescence spectrophotometry. The resultsindicate that the upconversion fluorescence of amine- and carboxyl-modified nanoparticles wasenhanced after the surfaces of nanoparticles were modified. Compared to the upconversionfluorescence intensity of non-modified nanoparticles, the upconversion fluorescence intensitiesof amine- and carboxyl-modified nanoparticles were enhanced by 9.4 and 1.4 times,respectively. These results are attributed to the formation of the chemical bonds betweenY2O3:Tm3+/Yb3+ core andnon-crystalline SiO2 shell via Y–O–Si bridges, which activate the ‘dormant’Tm3+/Yb3+ ions on the surfaces of nanoparticles. The results of the solubility investigations foramine- and carboxyl-modified nanoparticles indicate that severe aggregation can beweakened by adhering amino or carboxylic functional groups to the surfaces ofnanoparticles. It is therefore concluded that the good hydrophilicity resulting from activefunctional groups in solutions and more intense upconversion fluorescence enable the dopedcore–shell nanoparticles to have great potential to be used as fluorescence biolabels in thefuture.

Green and red upconversion luminescence in CeO 2:Er 3+ powders produced by 785 nm laser

CeO 2:Er 3+ powders were prepared by Pechini type sol–gel method. The structural properties of CeO 2:Er 3+ were studied by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra. The results show that CeO 2:Er 3+ has low phonon cutoff energy, which indicate that CeO 2:Er 3+ may have high luminescent efficiency. The green and red upconverted luminescence spectra of Er 3+ were investigated under excitation into the 4 I 9/2 level by 785 nm laser. The upconversion mechanisms were studied in detail through laser power dependence and Er 3+ ions concentration dependence of upconverted emissions, and results show that excited state absorption and energy transfer process are the possible mechanisms for the upconversion. The upconversion properties indicate that CeO 2:Er 3+ may be used in upconversion phosphors.

7Li NMR analysis on perovskite structured Li 0.15La 0.28TaO 3

The nanocrystalline perovskite material Li 0.15La 0.28TaO 3 has been synthesized by alkoxide-free Pechini type sol gel method. 7Li NMR measurements were carried out using a Bruker Avance 300 spectrometer at 116 MHz over the temperature range 150 to 400 K. Longitudinal spin-lattice relaxation times ( T 1) measured by saturation recovery and longitudinal relaxation times in the rotating frame ( T 1ρ) measured using the pulse sequence ( π/2–spin lock τ acquisition) with lock radio-frequency field υ = 62.5 kHz and the T 2 relaxation time measured by Hahn echo are presented. The static Hahn-echo spectra show two different lithium sites in this perovskite oxide. Further, the relaxation measurements T 1 and T 1ρ show two different types of lithium cations with fast and slow dynamics.

Photoluminescence enhancement of SnO 2:Eu by Mg 2+ doping

The influence of Mg 2+ doping on the crystallization behavior and enhancement in photoluminescence intensity of SnO 2:Eu was investigated. Highly homogeneous and pure samples were prepared by Pechini type sol–gel method and were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), absorption spectroscopy and photoluminescence. The results indicated that the incorporation of Mg 2+ ions into SnO 2 lattice could induce a remarkable increase of photoluminescence and the primary reasons were deduced.

Luminescence properties of Li + doped nanosized SnO 2:Eu

The influence of lithium doping on the crystallization behavior, morphology, and enhancement in photoluminescence intensity of SnO 2:Eu was investigated. In order to attain high homogeneous and pure samples, the Pechini type sol–gel method was adopted for the synthesis at low temperature (500 °C). The structure and morphology were characterized by using X-ray diffraction (XRD) and transmission electron microscope (TEM). The results indicate that the Li + doping could accelerate the crystallization of SnO 2 and the particle size of the phosphors is below 100 nm. In particularly, the incorporation of Li + ions into SnO 2 lattice could induce a remarkable increase of photoluminescence intensity.

Sol–gel synthesis and electrical properties of (ZrO2)0.85(REO1.5)0.15 (RE = Sc, Y) solid solutions

(ZrO2)0.85(REO1.5)0.15 (RE = Sc, Y) solid solutions in a pure cubic fluorite structure with uniform grain sizes ranging from nanometers to microns have been synthesized by a Pechini-type sol–gel method, using weakly cross-linked polymers. Metal nitrates, poly(ethylene glycol) and carboxylic acids such as acetic acid and formic acid, have been utilized to make the homogeneous polymer precursor solutions. Owing to its stronger acidity and coordinating capability, formic acid seems more effective in preventing the metal hydroxides segregating from the precursor solutions than does acetic acid during the gel formation. The Sc-doped zirconia derived from the formic acid-containing gel could achieve good-crystallization in the pure cubic phase at sintering temperatures as low as 1000 °C. Gel-calcined powders at 800 °C are mesoporous nanoparticles with narrow size distribution, and show a cubic structure attributed to the crystallite size effect. The polymeric precursor compositions display considerable impact on the gel formation, powder reactivity, crystallization of the sintered body, and finally the ionic conductivity of the grain boundary. However, the bulk ionic conductivity is dependent on the sintering temperature and variety of the dopants, rather than on the precursor compositions. Both the bulk and grain boundary conductivities increase when the sintering temperature/density are raised.