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Three series of Lu2O3:Eu ceramic materials doped with different concentrations of Eu3+ions (0.05−5 atom %) were prepared by sintering at the temperature of 1700 °C of nanocrystalline powders. The heat-treatments were performed in oxidizing, slightly reducing, and strongly reducing atmosphere of air, vacuum, and a N2−H2mixture (9:1 by volume), respectively. The radioluminescent properties of these materials have been systematically studied. After exposure to X-rays, independent of the atmosphere of the preparation, the ceramics exhibited an extensive afterglow, especially long and strong for low Eu concentrations. The afterglow and radioluminescence spectra differed significantly with the former showing much more emission resulting from Eu3+ions occupying the S6symmetry site in the host compared to the activator in the C2position. The effect was especially significant within the range of low and medium Eu concentrations, 0.05−1 atom %. From the decay traces of the persistent luminescence of Lu2O3:Eu ceramics it was concluded that the mechanism of the process is governed by the second order kinetics. It is postulated that only Eu3+ions located within the layer containing both S6and C2metal ion sites are active in the afterglow emission, while those placed within the layer consisting of only the C2metal ion sites do not contribute to the afterglow. Another option is that electronic levels of Eu3+in S6site are more favorably positioned to intercept migrating from their traps excited carriers.

Nanocrystalline powders of Lu2O3:Eu with activator content varying between 0.2%-10% were prepared using four different methods of synthesis. The products differed in their microstructure and crystallites sizes. Combustion of Lu(NO3)3 with urea produced strongly agglomerated material, most probably with significantly non-uniform distribution of the Eu3+ dopant. Replacing urea with glycine for the combustion produced only slightly agglomerated, voluminous, fluffy powder. Applying the Pechini technique resulted in significantly agglomerated powder while the homogeneous precipitation of Lu(OH)3 with urea at 90 °C and its subsequent decomposition to Lu2O3 at 650 °C resulted in a powder of perfectly spherical particles with a uniform size of about 130 nm with very low agglomeration. The efficiency of X-ray excited luminescence of our nanocrystalline Lu2O3:5%Eu was compared to that of the commercial microcrystalline Gd2O2S:Eu. It was found that the commercial phosphor performed four times more efficiently than our nanocrystalline powder. We consider this to be rather encouraging as the fabrication of our powder is not optimized yet. It seems that Lu2O3:Eu, even in nanocrystalline form, can perform much more efficiently which would make it a promising X-ray phosphor.

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