RESUMO
Compounds with the general formula RE3MO7 (RE = rare earth ions; M = Ta, Nb, Sb, Ru, Ir, Os, Re, etc.), crystallize as a fluorite-related structure, forming polymorphs with different space groups. The space group strongly depends on the RE3+ and M5+ ionic radii and processing conditions. Structural characterization is well-established for the lanthanide series, but literature studies have divergent views about how to attribute yttrium tantalate (Y3TaO7) space groups-some authors have described the Y3TaO7 structure as orthorhombic and belonging to space group C2221 or Ccmm, whereas others have assigned a cubic Fm3Ìm structure to it. Here, we have characterized the structure of undoped and Eu3+-doped Y3TaO7 (0.1 to 50 mol% of Eu3+) samples synthesized by the sol-gel method that crystallized as a cubic disordered fluorite-type structure, space group Fm3Ìm. Their powder X-ray diffraction measurements, Rietveld analyzes and Raman spectra were used as a conclusive technique of the structural properties. We have also investigated whether a secondary phase (M'-YTaO4) emerged in the samples and compared the phase composition of each sample to their Raman spectra. Low-temperature photoluminescence measurements (â¼15 K) using Eu3+ as a structural probe helped us analyze the inhomogeneous broadening observed in the emission spectra. These measurements can be used as an important tool to attribute the crystalline phases of rare earth tantalates and niobates.
RESUMO
In recent years, the use of quantum dots (Qdots) to obtain biological images has attracted attention due to their excellent luminescent properties and the possibility of their association with contrast agents for magnetic resonance imaging (MRI). In this study, Gd3+/ZnO (ZnOGd) were conjugated with Qdots composed of a gadolinium-copper-indium-sulphur core covered with a ZnS shell (GCIS/ZnS Qdots). This conjugation is an innovation that has not yet been described in the literature, and which aims to improve Qdot photoluminescent properties. Structural and morphological Qdots features were obtained by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analyses (TGA). The photoluminescent properties were examined by emission (PL) and excitation (PLE) spectra. A new ZnOGd and GCIS/ZnS (ZnOGd-GCIS/ZnS) nanomaterial was synthesized with tunable optical properties depending on the ratio between the two native Qdots. A hydrophilic or lipophilic coating, using 3-glycidyloxypropyltrimethoxysilane (GPTMS) or hexadecyltrimethoxysilane (HTMS) on the surface of ZnOGd-GCIS/ZnS Qdots, was carried out before assessing their efficiency as magnetic resonance contrast agents. ZnOGd-GCIS/ZnS had excellent luminescence and MRI properties. The new Qdots developed ZnOGd-GCIS/ZnS, mostly constituted of ZnOGd (75%), which had less cytotoxicity when compared to ZnOGd, as well as greater cellular uptake.
RESUMO
We report the synthesis of a Y3TaO7 solid solution containing a high Eu3+ concentration (from 7 up to 50 mol%) and investigate how Eu3+ influences the Y3TaO7 crystallization process. To this end, we evaluate the Y3TaO7 structural features and photoluminescence properties after Eu3+ introduction into the Y3TaO7 lattice. The higher the Eu3+ ion concentration, the more stable the crystallization process of the Y3TaO7 phase seems to be. The Eu3+-containing Y3TaO7 displays intense orange-reddish, broad band emission because Eu3+ occupies different symmetry sites in the host and causes inhomogeneous broadening. Eu3+ emission quenching due to Eu3+ concentration is negligible up to 30 mol% and absolute quantum yield values of up to nearly 30% were obtained, making Eu3+-containing Y3TaO7 interesting materials for application as high-intensity emitters in photonics.
