| Summary: | Glassy nanocomposites containing Yb<sup>3+</sup>/Er<sup>3+</sup>-doped GdF<sub>3</sub> and LiGdF<sub>4</sub> nanocrystals have been prepared by controlled crystallization of the xerogel and the structural, up-conversion luminescence, and magnetic properties were analyzed and discussed. Structural and morphological analysis showed uniform distribution of both GdF<sub>3</sub> and LiGdF<sub>4</sub> nanocrystals (tens of nm size), embedded in silica glass matrix as the result of thermal decomposition of the trifluoracetates, revealed as a strong exothermic peak at about 300 °C; the Li-ions co-doping showed a strong influence on the GdF<sub>3</sub> and LiGdF<sub>4</sub> nanocrystalline fraction. The energy dispersive spectrometry mapping showed Gd, F and Yb, Er within the nanocrystals but not in the silica glass matrix. X-ray diffraction pattern analysis indicated the crystalline lattice distortion consistent with the Yb/Er incorporation in both fluoride nanocrystals. The <i>“green”</i> ((<sup>2</sup>H<sub>11/2</sub>, <sup>4</sup>S<sub>3/2</sub>) →<sup>4</sup>I<sub>15/2</sub>) and <i>“red”</i> (<sup>4</sup>F<sub>9/2</sub>→<sup>4</sup>I<sub>15/2</sub>) up-conversion luminescences at 525, 545, and 660 nm observed under 980 nm laser light pumping were assigned to the Er<sup>3+</sup> ions deexcitation through a two-photon process. The magnetic properties of the nanocomposite are strongly temperature dependent. The magnetization hysteresis loops show a ferromagnetic behavior at low temperatures (5K) related to the rare-earth ions contribution and the saturation magnetization of 39 emu/g. At 300 K a paramagnetic behavior was observed that was ascribed to the non-interacting localized nature of the magnetic moment of the rare-earth ions. Hence, such novel, multifunctional magnetic and optical materials can allow the intertwining between magnetism and photonics and might offer new opportunities for new magneto-optical device development.
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