Within last several years, researchers have shifted the focus of their investigations toward the nanotechnology of new nano-objects based on rare-earth oxides ((R1_1-хR2_x)₂O₃, R1 = Y, Gd, Lu, R2 = Eu, Yb, Nd) from individual nanoparticles to bulk materials with ordered nanostructure. This new interest has emerged due to the prospective applications in photonics, lasers, energy and environmental technologies. To extend phosphor nanopowders to high resolution applications fine individual particles with ideal spherical morphology, controllable diameters, narrow size distribution as well as perfect crystalline structure and homogeneous composition can be highly desirable.

However, the principal drawback of the luminescent nano- and submicrospheres (R1_1-хR2_x)₂O₃ (D=70-400 nm) is lower luminescence efficiency comparatively with bulk materials due to the surface quenching processes through the decrease of the volume/surface ratio of the phosphor layer. That is why, it is necessary to establishment of the thermolysis parameters and crystallization processes of the spheres to minimize the activator activity diffusion, as well as select the optimal activator concentration to eliminate the of luminescence quenching. It was demonstrated in the present study for the model crystalline spheres phosphor (R_1-xEu_x)₂O₃ (R=Lu, Y) (⁵D₀ → ⁷F₂ transition).

Polycrystalline, non-agglomerated nanopowders based on monosized (R_1-xEu_x)₂O₃ nano- and submicrospheres were prepared by low-temperature thermal decomposition of the amorphous precursor. The resulting structural, morphological and luminescence properties of obtained products were studied using the X-ray diffraction, X-ray photoelectron and FT-IR spectroscopy, SEM and HR-TEM microscopy methods. The mechanisms of the precursor decomposition, spheres crystallization and morphological evolution at the temperatures ranging from 60ºC to 1200ºC were studied. It was shown that the annealing temperature strongly influences on the structure, morphology and composition of the spherical (R_1-xEu_x)₂O₃ phosphors obtained. The effects of annealing temperature as well as particles sizes and dopant Eu³⁺ concentration on the luminescence efficiency of (R_1-xEu_x)₂O₃ phosphors were systematically investigated. It was shown that the concentration quenching effects of Eu³⁺ luminescence in the (R_1-xEu_x)₂O₃ spheres with 100-250 nm diameter is shifted to lower Eu³⁺ concentrations (x = 0.05) compared with the microcrystalline powders with similar composition (x = 0.09). The reason of this phenomenon probably is formation of inhomogeneous phase of (R_1-xEu_x)₂O₃ solid solution in the nanolayers with the primary location of bigger Eu³⁺ ions in the surface area due to active diffusion processes.

Detailed analytical data revealed that the luminescence intensity increased with the increase of crystallites size and particles size. The phosphor spheres developed in this work are attractive as building blocks for scintillation films for X-ray imaging and also for new types of photonic structures.

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