Phase composition and photoluminescence correlations in nanocrystalline ZrO$_2$:Eu$^{3+}$ phosphors synthesized under hydrothermal conditions

Luminescent zirconia nanoparticles with europium ion content 1 and 10 mol.% were synthesized under hydrothermal conditions. Annealing of ZrO$_2$: 1 mol. Eu$^{3+}$ nanoparticles made it possible to obtain a sample with a high monoclinic phase content up to 92 %. An increase in the concentration of Eu$^{3+}$ ions introduced into the zirconia crystal lattice has made it possible to almost completely convert its monoclinic and tetragonal phases into cubic modification. The phase composition of the synthesized samples was determined by powder X-ray diffraction, electron microdiffraction, and Raman spectroscopy. Analysis of the crystallographic data and the luminescent spectra helped to reveal correlations between the ZrO$_2$:Eu$^{3+}$ nanophosphor structure and the energy redistribution of Eu$^{3+}$ optical transitions at 614–626 nm and 606–633 nm wavelengths. In addition, a relationship was established between the phase composition of nanoparticles based on zirconia and the luminescence lifetime of Eu$^{3+}$ ions.