[en] The nanometric precursors of neodymium oxide of various morphology from fibrous to well-dispersed spheroidal were prepared via a solvothermal reaction routes. The precursors and their thermal evolution to neodymium oxide phase were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was found that the reaction parameters, kind of solvent as well as neodymium salt used played a key role for the product formation of desired morphology and structure. Similarly, kind of neodymium oxide precursor determined the morphology and the crystal structure (haxagonal or cubic) of the final oxide. The potential application of Nd₂O₃ precursors prepared by solvothermal method as convenient material for preparation of homogeneous thin coatings on planar substrates is shown

[en] This works presents comprehensive studies on fundamental excitations trapping and the resulting charge destabilization in cubanite Ag_xS/AgInS₂ quantum-confined random alloys. The observed optical activity of defect levels, related to silver alloying, is discussed basing on the femtosecond excited time-resolved photoluminescence spectrograms as well as theoretical predictions obtained via the density functional theory within the reduced cluster model. Impact of the charge trapping on the third-order optical hyper-polarizabilities has also been investigated basing on the two-photon excitation action cross sections. It has been shown that silver induced defects in the Ag_xS/AgInS₂ random alloys are responsible for effective electron/hole trapping and strong temporal charge uncompensation. The silver on indium Ag_In, silver interstitials Ag_i and higher-order defect clusters e.g. (Ag_In^2--2Ag_i⁺) formed effectively due to defect compensation mechanism have been considered in this work as providing possible pathways of defect mediated depopulation of the excited states. The electron/hole trapping mechanism is also discussed as a major mechanism responsible for fast trionic relaxations leading to strong deviation from the first-order decay law and significant temporal red-shifts of the photoluminescence band maximum. Further, it is shown that controlling the silver alloying ratio and the resulting number of defects charge states, it is possible to cause variation of the average photoluminescence decay times by an order of magnitude. The silver alloying was also found as an efficient route for significant increase of the two-photon excitation action cross section.

[en] Highlights: • Hexagonal polymorph of GdAlO₃ (GAH) was synthesized and characterized. • Electron diffraction revealed superstructure reflections in GAH due to defects ordering. • GAH transforms into perovskite GdAlO3 (GAP) at 1000 °C. • Contrary to GAP, GAH does not show magnetic ordering at low temperature. • TEM and Dy luminescence indicate strong structure disorder in GAH. -- Abstract: The structure and basic properties of a hexagonal polymorph of GdAlO₃ aluminate (GAH) were studied using a set of experimental methods (XRD, FTIR, Raman spectroscopy, diffuse reflectance spectroscopy, luminescence spectroscopy, magnetic susceptibility, and TEM). The GAH crystallized at 900 °C from an amorphous precursor and decomposed into perovskite GdAlO₃ (GAP) at 1000 °C. XRD pattern of polycrystalline GAH could be indexed in P6₃/mmc space group with unit cell parameters a = 0.3734 nm, c = 1.0535 nm, following literature data. The electron diffraction revealed, however, the presence of well-defined superstructure reflections due to defects ordering. Contrary to a recent report suggesting the presence of CO₃ groups in the structure of similar hexagonal YAlO₃, we did not observe such groups in the FTIR spectra of GAH. On the other hand, the stoichiometry of GAH differs from ideal GdAlO₃, with Al/Gd atomic ratio close to 1.2, similar to reported for hexagonal YAlO₃. GAH exhibits paramagnetic behavior over 1.8–300 K temperature range, with the effective Gd magnetic moment μ_eff = 7.90 μ_B, close to the theoretical value for free Gd³⁺ ion. No paramagnetic – antiferromagnetic phase transition at ~4 K, characteristic for perovskite-type GdAlO_3, was observed. The reason is probably a less ^dense structure of GAH, with longer Gd-Gd and Gd-O-Gd interatomic distances. Emission spectra of Dy doped (~1 at%) GAH and GAP revealed dramatic differences in Dy³⁺ emission bands, despite similar mean crystallite size of the host material. An almost structureless ⁴F_9/2→⁶H_13/2 and ⁴F_9/2→⁶H_15/2 emission bands, observed for GAH, indicate, following TEM data, that Dy ions occupy numerous nonequivalent sites due to the presence of a large concentration of crystal defects.

[en] This paper reports results of studies on the interaction of praseodymium oxide nanocrystals with an amorphous silica. Nano-sized (3-4 nm) amorphous precursor of praseodymium oxide synthesized using a microemulsion technique were supported onto a high surface SiO₂ or occluded into SiO₂ matrix. Solid state reactions occurring in these binary systems upon heat treatment in air, argon or hydrogen at 800-1100 ^oC were studied by TEM, XRD, FT-IR and UV-vis spectroscopy. It has been found that morphology of the sample as well as annealing atmosphere influence greatly the phase evolution. At temperatures above 900 ^oC, nanocrystalline praseodymium silicates of various morphology and crystal structure were obtained. In particular, a new polymorph of Pr₂Si₂O₇, isostructural with I-type Ln₂Si₂O₇ (Ln₆[Si₄O₁₃][SiO₄]₂) Ln = Ce, La, has been identified

[en] Raw powders of BaHfO₃:Ce were prepared with modified Pechini process and were calcined in the 650-1700 ^oC range of temperatures, at different atmospheres - air, vacuum and nitrogen-hydrogen mixture. The powders were converted into sintered ceramics by vacuum sintering. The materials were characterized by XRD, TEM, photoluminescence and radioluminescence spectroscopy. UV-VUV excitation spectra were recorded using synchrotron radiation. Excitation spectra proved that atmosphere of preparation significantly influences the host-to-activator energy transfer, which is the most efficient for materials made in reducing conditions. Also radioluminescence efficacy was found to be superior for materials prepared in such conditions.

[en] Fabrication procedure of nanocrystalline Lu₂O₃:Eu powders from organic-inorganic emulsion is presented and the behavior of the precipitate upon heat-treatment is analyzed. It is proved that heating at 800-850 deg. C converts the raw material into Lu₂O₂SO₄:Eu, which decomposes further to Lu₂O₃:Eu when heated at 1000 deg. C or above. Research with synchrotron radiation revealed that free exciton is able to transfer effectively its energy to Eu³⁺ ions in Lu₂O₃:Eu nanosized powder, which is in contrast to the findings for micron-sized ceramics of the same composition

[en] Reaction of nanocrystalline lutetium oxide with amorphous SiO₂ was studied at 600-1200 deg. C with X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR), FT-Raman spectroscopy and Yb³⁺ emission spectroscopy. It has been shown that up to loading corresponding to ca. 10 μmol Lu₂O₃/1 m² SiO₂, Lu can be dispersed over SiO₂ as an amorphous, nanometre thick Lu-O-Si layer. At 1000 deg. C formation of crystalline silicate, isomorphous with B-type Ln₄[Si₃O₁₀][SiO₄] (Ln=Dy-Tm) was observed. It has been shown that emission bands of Yb³⁺, introduced as contamination present in Lu₂O₃, appearing in anti-Stokes region of Raman spectra, could be used as convenient tool for identification of the Lu-phases formed in the samples

[en] Nano-sized (4-5 nm) crystallites of CeO₂ and CeLnOx mixed oxides (Ln = Pr, Tb, Lu; Ce/Ln atomic ratio 5/1) with narrow size distribution were prepared by a microemulsion method (W/O). Structure, morphology and reducibility of the samples annealed up to 950 deg. C in oxygen were analyzed by HRTEM, XRD, Raman spectroscopy and H₂-TPR. Obtained mixed oxides exhibited fluorite structure of CeO₂, and no phase separation occurred upon heating up to 950 deg. C. Both XRD and TEM revealed that severe sintering of CeO₂ at high temperatures could be effectively hampered by addition of second lanthanide. HRTEM results showed that the nanocrystallites exhibited irregular shapes exposing mostly {1 1 1} faces, though small amount {1 0 0} faces was also observed. No distinguishable change in morphology of the particles could be detected with temperature increasing from 800 to 950 deg. C

[en] Solid-state interface reactions in highly dispersed Nd₂O₃-SiO₂ binary oxide system were studied at temperatures 600-1200 deg. C with X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR). The results show that at 600-900 deg. C, an amorphous, nanometer thick Nd-O-Si layer covering SiO₂ particles exists in the system. At higher temperatures, the breakage of the layer into amorphous islands occurs and crystalline silicates with various structures are formed. In particular, Nd₆[Si₄O₁₃][SiO₄]₂ silicate, analogue of recently discovered Ce and La silicates, forms together with well known A-Nd₂Si₂O₇ silicate at temperatures from 950 up to 1100 deg. C. For samples with high surface coverage (13.6 and 33.3 μmole Nd₂O₃/1 m² SiO₂), oxyapatite Nd_9.33[SiO₄]₆O₂ silicate occurs as intermediate phase at temperatures below 1100 deg. C. Apparent similarity of an amorphous silicate surface layer to thermodynamically stable disordered nanometer thick films reported recently for Bi₂O₃-ZnO system is discussed

[en] Yttrium aluminum garnet, Y₃Al₅O₁₂ (YAG), doped with Eu (0-4%) was synthesized reacting appropriate metal nitrates in NaNO₂-KNO₂ eutectic mixture. Pure cubic garnet phase was formed upon heating for a few hours at temperature as low as 470 ^oC. The particle sizes of the powders were mostly in the range of 200-300 nm, but a small fraction of material crystallized in particles of about 20-40 nm. Selected area electron diffraction patterns proved that the larger particles are monocrystalline. Excitation and emission spectra of the Eu-doped powders are characteristic for Eu³⁺ in an oxide host. The most intense luminescence lines are located around 590 nm