Abstract
Quasi-spherical nanoparticles of ZrO2 containing EuO1.5 from 2 to 15 mol.% were synthesized from the chlorides of the corresponding metals under hydrothermal conditions. The structural changes of Zr1–xEuxO2–0.5x (x = 0.02 ÷ 0.15) nanoparticles depending on the content of europium (III) ions were studied using the complementary methods (X-ray diffraction, electron microdiffraction, Raman and photoluminescence spectroscopy). It was shown that increasing the Eu3+ concentration in the Zr1–xEuxO2–0.5x nanoparticles leads to a transition from the equilibrium monoclinic zirconia phase to metastable tetragonal and cubic polymorphic modifications. In this case, the size of the nanoparticles decreases from 11.5 nm to 9 nm; the specific surface area grows from 80.2 to 111.3 m2/g, and the electrokinetic potential increases monotonously from −8.7 to 16.3 mV. The evolution of the phase composition of Zr1–xEuxO2-0.5x nanoparticles from monoclinic to tetragonal/cubic allomorphs with an increase in the molar fraction of stabilizer ions was correlated with changes in the sublevel structure of 5D0 → 7F2 and 5D0 → 7F4 optical transitions for Eu3+ in the luminescence spectra. Besides, for the nanoparticles obtained by hydrothermal synthesis from chlorides, the quantum efficiency does not exceed 3%. According to the M.T.T. assay, as a result of three-day human fibroblast cultivation in the aqueous dispersion of Zr1–xEuxO2–0.5x (x = 0.02 ÷ 0.15) nanoparticles, the proliferation activity of the cells is maintained, indicating that they do not have cytotoxic properties. Such nanoparticles can be used in organic–inorganic composites for medical applications in order to strengthen the polymer scaffolds and visualize changes in their structure within time.
Highlights
More and more attention has been paid to the development of highly sensitive and safe nanophosphors for probing and visualizing biological objects [1,2,3]
One can talk about the predominating tetragonal phase, which is more plausible, especially if we take into account the (102) diffraction peak of t-ZrO2 . (Along with the tetragonal phase, at high concentrations of europium (III) ions in ZrO2, the cubic one is observed using Rietveld refinement
We found that in the luminescence spectra, the m-ZrO2 phase manifests itself against a tetragonal/cubic contribution, which is associated with the possible uneven segregation of europium (III) ions
Summary
More and more attention has been paid to the development of highly sensitive and safe nanophosphors for probing and visualizing biological objects [1,2,3]. Inorganic nanoparticles doped with lanthanide ions (Ln3+ ) for use in biomedical applications should be biocompatible, exhibit intense luminescence and low toxicity, and have good colloidal stability in water and biological solutions [4,5]. There is the possibility of the indirect P.L. excitation of the Ln3+ , with narrow f-f emission lines and long lifetime, through oxide nanoparticles, acting as nanoantennas [11,12]. If Ln3+ ions are embedded into a suitable crystal lattice, the sequential absorption of several photons through the lanthanide energy levels can occur in oxide nanoparticles, which provides higher energy to the anti-Stokes luminescence [13]
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