Structural and luminescent properties of nanostructured KGdF4:Eu3+ synthesised by coprecipitation method (original) (raw)
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Journal of Alloys and Compounds, 2005
The Eu 3+ :KGdF 4 powders with average crystallite size of 20 and 25 nm have been obtained from solution by co-precipitation method. Morphology of the as-received powders was examined by XRD and TEM methods. Behaviour of these two powdered batches, characterised by different size of nanocrystallites, versus thermal treatment has been studied by X-ray powder diffraction, thermogravimetric, infrared spectroscopy and emission spectroscopy methods. The phase transitions between low-temperature cubic, orthorhombic, trigonal and hightemperature cubic modifications of KGdF 4 were detected for both samples heated in 300-790 • C temperature range. Abundance of the particular polymorphic form observed at given temperature differs considerably for samples of different initial crystallite size. Besides, significant differences in number of lattice defects, water contents and emission properties were observed for these two samples. The properties of material precipitated from solution are also compared with structural and optical properties of the Eu 3+ :KGdF 4 fluoride synthesised by a solid-state reaction.
Structural and luminescent properties of nano-sized NaGdF 4:Eu 3+ synthesised by wet-chemistry route
Journal of Alloys and Compounds, 2004
Hexagonal Eu 3+ :NaGdF 4 fluoride with average grains size of 20 nm was obtained from solution by a co-precipitation method. Morphology of the obtained powder was examined by XRD and TEM methods. Absence of the Eu 3+ -O 2− charge-transfer band, expected in excitation spectrum at ∼260 nm indicates, that oxygen ions are not incorporated into a fluoride lattice. As-received fluoride contains considerable amounts of the water molecules, adsorbed at the surface of the material, which may be relatively easily removed by heating the powder at 300 • C. Thermal treatment at 650 • C is sufficient for removing of the OH − groups built into fluoride lattice. Influence of method of synthesis as well as oxygen, water molecules and OH − groups content on optical properties of the obtained phosphors is investigated and discussed by comparison with optical properties of the Eu 3+ :NaGdF 4 fluoride synthesised by a solid-state reaction.
Crystal Growth & Design, 2010
Sodium gadolinium fluoride nanocrystals have been prepared in the solvent N-(2-hydroxyethyl)-ethylenediamine (HEEDA) at 200°C. The formation of the cubic and the hexagonal phase in the synthesis can be controlled by properly adjusting the concentration of fluoride and the ratio between sodium and gadolinium. The absence of the Eu 3þ-O 2charge transfer band in the excitation spectrum of Eu 3þ-doped nanocrystals indicates that the concentration of oxygen ions is low in all samples.
Investigation of Structural, Electronic and Optical Properties of KCdF3
American Journal of Modern Physics, 2013
The structural, electronic and optical properties of KCdF 3 are investigated using the density functional theory (DFT) within the generalized gradient approximation (GGA). The calculated lattice parameters have been compared to experimental results and demonstrated to be in good agreement with them. The calculated electronic band structure of cubic KCdF 3 shows that crystal has a indirect forbidden band gap with value of 2.95 eV from the high symmetry point R to gamma point in the first Brillouin Zone (BZ). The optical spectra are investigated under the scissor approximation in the photon energy range, up to 30 eV. The dielectric function and some optical constants such as energy loss functions, reflectivity, extinction, and absorption coefficients, effective number of valance electrons and refractive index are calculated.
Dalton Transactions, 2014
The structure of gadolinium oxyfluoride nanoparticles was revised. Extensive studies including X-ray diffraction and Rietveld refinement as well as Fourier transform infrared spectroscopy and Raman spectroscopy confirmed the monoclinic P12/c1 crystal structure of Gd 4 O 3 F 6 . Morphological analysis using transmission electron microscopy showed the nanocrystallinity of the materials prepared via the sol-gel
Selective excitation of Eu3+ in the core of small β-NaGdF4 nanocrystals
Journal of Materials Chemistry C, 2012
The influence of the nanocrystal matrix on the optical properties of lanthanide dopants is investigated with europium ions used as local crystal field probes. The analysis is performed on small NaYF 4 and NaGdF 4 nanocrystals obtained by the thermolysis of the corresponding metal trifluoroacetates. An important role in the synthesis is played by trioctylphosphine oxide which induces the crystallization of nanocrystals with small diameters ($5 to 6 nm). In such small particles, the energy transfer from gadolinium to europium ions is studied with photoluminescence, photoluminescence excitation and time-resolved experiments. We demonstrate that excited gadolinium ions efficiently transfer their energy to europium, and their photoluminescence spectra depend on the nanocrystal size. This is contrary to the direct excitation of Eu 3+ ions, which produces size-dependent emission corresponding to the surface to volume ratio of europium sites. Finally, we propose that Gd 3+ ions transfer their energy mainly to the Eu 3+ in the core of the nanocrystals. These observations provide a base for the optically controlled emission from only the core of the nanocrystals.
VUV excited luminescence of MGdF4:Eu3+ (M=Na, K, NH4)
Journal of Luminescence, 2004
Eu 3+-doped NaGdF 4 , KGdF 4 and NH 4 GdF 4 phosphors with little oxygen contamination have been synthesized by hydrothermal technique. The emission spectra show that the doped Eu 3+ ions are located in noncentrosymmetric sites in the three compounds. The two-photon emission has been observed in NaGdF 4 :Eu 3+ and KGdF 4 :Eu 3+ compounds under VUV excitation from the ground states to higher 6 G J excited states of Gd 3+ ions, while in Eu 3+-doped NH 4 GdF 4 , emissions from 5 D 1,2,3 excited states of Eu 3+ cannot be detected in the luminescence spectra.
Energetics of formation of KFGdF3 binary-intermediate compounds
Thermochimica Acta, 1996
Enthalpies of formation were measured for KGdF~, K2GdF s and KGdzF 7 using the transposed temperature drop calorimetry method. These compounds were synthesized by conventional solid state reaction methods using mixtures of KF and GdF 3. The measured enthalpies of formation from fluorides for KGdF4, K2GdF 5 and KGd2F 7 were-22.3,-16.1 and-18.3 kJ mol-1, respectively. From these measurements, enthalpies of formation from the elements were computed to be-2290.0,-2852.4 and-3985.2 kJ mol 1 for the respective compounds. These enthalpies were compared with estimated values calculated by two methods previously reported to be effective for multicomponent oxides. Estimated values compare favorably with measured data, with deviations ranging from 0.5 to 2.9%. The errors of 0.5 2.9% correspond to a 16 85 kJ mol 1 uncertainty range for AfH ° of ternary fluorides from binary fluorides. One of these methods, based on the summation of AfH ° values for the constituent binary fluorides, is recommended for the K Gd F compounds.
Optical properties and Judd–Ofelt parameters of Dy3+ doped K2GdF5 single crystal
Optical Materials, 2013
Dy 3+-doped K 2 GdF 5 single crystals with 10.0 mol% have been prepared by hydrothermal condition. The spectra are analyzed in term of the Judd-Ofelt theory, the intensity parameters (X k , k = 2, 4, 6) have been evaluated for Dy 3+-doped K 2 GdF 5 sample. The electric (S ed), magnetic (S md) dipole line strength, radiative (A), and total radiative (A T) transition probabilities, lifetime (s R), branching ratios (b R) for the excited levels of Dy 3+ doped K 2 GdF 5 crystals were investigated by using the intensity parameters. In addition, the stimulated emission cross-sections (r kp) and integrated emission cross-section (R if) have been predicted for the transitions from excited level, 4 F 9/2 , to the 6 H 15/2 , 6 H 13/2 and 6 H 11/2 levels. The energy transfer occurs from Gd 3+ to Dy 3+ , resulting in the additional intense excitation UV-narrow bands for the luminescence of the Dy 3+ ions.