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Electronic and structural properties of cubic Lu2O3with either single oxygen vacancy, oxygen vacancy–vacancy pair, or a Frenkel pair (an oxygen vacancy and an interstitial oxygen) were analyzed using ab initiodensity functional theory calculations. A plane-wave ultrasoft pseudopotential approach with local density approximation functional was used to optimize the geometries. A full-potential linearized augmented plane-wave method with meta-generalized gradient approximation was applied to the optimized geometries to calculate the electronic properties of the systems. Defect-related bands were observed between the valence band and the conduction band. Different charge states of the defects were considered. Both oxygen vacancy and oxygen vacancy–vacancy pairs behave as moderately deep electron traps (trap depth 1.3–2.7 eV). Trapped electron localization at the vacancy site(s) was confirmed using electron density and electron localization function plots. The bands originating from oxygen vacancy–vacancy pairs in Lu2O3exhibit some dependence on the distance between the two entities. The resulting energy differences (considered from an optical absorption point of view) cover ultraviolet, visible, and infrared ranges. Thus, it is plausible that oxygen vacancy–vacancy pairs are responsible for the coloration that is sometimes observed in Lu2O3powders and crystals. On the contrary, the Frenkel pair exhibits no systematic dependence of the defect-related bands on the distance between its oxygen vacancy and interstitial oxygen, while the resulting defect-related bands look similar to those corresponding to the isolated defects. Frenkel pairs are thus considered a probable mechanism of oxygen vacancy formation and stabilization of Lu2O3. Additionally, a brief review of the relevant experimental data is provided in the introduction.

The persistent luminescence (PersL) dependence on the dopants and derived mechanism of trapping and de-trapping processes were investigated in Y3Al2Ga3O12(YAGG) based nanophosphor, doped with Ce3+and/or Cr3+. It is found that the presence of Cr3+ions produce electron and hole traps and capture suitable charge after X-ray irradiation. The effect of irradiation on the carriers trapping and their pathways after excitation was studied by means of thermo luminescence technique. On the other hand, for blue light irradiation the mechanism seems to be different. In the latter case, the Ce3+ions, having the position of energy levels in the conduction band, become sensitizers for the electrons and main emission centres for the PersL (de-trapping process goes through Ce3+).

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.

Europium-doped Lu2O3 nanocrystalline powders with Eu concentrations of 1−13 ^m/0 were prepared via a combustion route. Their morphology was determined with TEM measurements. It was found that the sizes of nanocrystallites were around 10−13 nm. These powders were sintered at 1700 °C into tablets whose grains were a few micrometers wide. Absorption and emission spectra of all materials were measured. Pronounced changes of UV absorption bands with increasing concentration were observed in the case of nanoparticulate powders. The Eu emission lifetimes of nanopowders demonstrated significant concentration quenching. No such effect was observed for the sintered materials up to 13 ^m/0 of Eu. A strong decrease of the emission rise time with rising Eu concentration was found for both types of the material at room temperature. At the temperature of liquid nitrogen, the longest rise time in the case of nanomaterials (~110 μs) was found for a sample containing 5% of Eu, whereas for the sintered ceramics, the behavior was very similar to that at room temperature. Spectroscopic results are elucidated by a concept of strong aggregation of Eu³⁺ ions in nanocrystallites when the ion exceeds 3%. An aggregation of Eu³⁺ ions can be deduced from the nonexponential decay kinetics and leads to fast energy migration, resulting in the linear concentration dependence of the decay rate.

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The present status of the LuAlO/sub 3/:Ce (LuAP) scintillator is reviewed and its performance compared to that of YAlO/sub 3/:Ce (YAP). The light output of LuAP, at this stage of development, appears to be limited by two factors: insufficient Ce concentration and the presence of a parasitic absorption, Both LuAP and YAP show a dependence of light output on thickness, indicating that YAP also suffers from parasitic absorption. Measurements on undoped material offer a clue to the identity of the "parasite".

Properties of SrS:Ce and LuPO4:Eu sintered ceramics are reported for the first time. Both materials were sintered at various temperatures up to 1700°C. SrS:Ce sintered ceramics were found to form a new luminescent center(s) giving emission with maximum around 620 nm or 700 nm for 0.05% Ce and 5% Ce, respectively. This red-infrared band was continuously more potent with increasing sintering temperature and also for higher Ce concentrations both in photo- and radioluminescence. The new luminescent feature was shown to be formed by Ce3+ions with strongly perturbed symmetry compared to the octahedral one offered by the SrS host. After irradiation with X-rays LuPO4:Eu sintered ceramics produced a long lasting afterglow luminescence which was connected with thermoluminescence around 200°C. The shape of the glow curve bands change with Eu concentration. For Eu content of 0.1% the TL band was quite symmetrical. For 5% of Eu the TL glow band appeared more structured and the 200°C peak was associated with intense components around 150°C and 330°C. The former contributed into more potent afterglow at room temperature. Sintering of SrS:Ce and LuPO4:Eu induced new luminescent characteristics of both compositions endowing them with new, potentially usable functionalities.

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