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In this work a strategy for the control of structure and optical properties of inorganic luminescent oxide-based nanoparticles is presented. The nonaqueous sol-gel route is found to be suitable for the synthesis of hafnia nanoparticles and their doping with rare earths (RE) ions, which gives rise to their luminescence either under UV and X-ray irradiation. Moreover, we have revealed the capability of the technique to achieve the low-temperature stabilization of the cubic phase through the effective incorporation of trivalent RE ions into the crystal lattice. Particular attention has been paid to doping with europium, causing a red luminescence, and with lutetium. Structure and morphology characterization by XRD, TEM/SEM, elemental analysis, and Raman/IR vibrational spectroscopies have confirmed the occurrence of the HfO2 cubic polymorph for dopant concentrations exceeding a threshold value of nominal 5 mol %, for either Lu(3+) or Eu(3+). The optical properties of the nanopowders were investigated by room temperature radio- and photoluminescence experiments. Specific features of Eu(3+) luminescence sensitive to the local crystal field were employed for probing the lattice modifications at the atomic scale. Moreover, we detected an intrinsic blue emission, allowing for a luminescence color switch depending on excitation wavelength in the UV region. We also demonstrate the possibility of changing the emission spectrum by multiple RE doping in minor concentration, while deputing the cubic phase stabilization to a larger concentration of optically inactive Lu(3+) ions. The peculiar properties arising from the solvothermal nonaqueous synthesis here used are described through the comparison with thermally treated powders.

New materials are studied for fast and heavy scintillators, which are increasingly used and/or demanded in coming medical and industrial applications. Among others, Ce-doped Lu-containing compounds are under study and development, especially LSO:Ce 3+ and LuAP:Ce 3+ crystals. However, the growth of single crystals of these compounds appeared very difficult, especially the latter system has not been offered by any industrial company yet, even if the first papers dealing with this promising scintillator were published in 1995 by several groups [for review, see [1]).Contrary to LuAP perovskite phase, the garnet one Lu 3 Al 5 O 12 (LuAG) appears as rather stable and can be thus grown more easily. LuAG single crystals have a density of 6.73 g/cm 3 (94% of BGO) and the leading fast emission/scintillation decay component is about 50 ns (six times faster than BGO) peaking between 500 and 550 nm (similar spectral region as BGO emission). Despite of the fact that such material can appear as serious competitor of BGO scintillator, little attention was paid to it in the literature up to now [2].This note provides a direct comparison between YAP:Ce 3+ and LuAG:Ce 3+ scintillators grown in the same laboratory 1 ) as for radioluminescence light output, scintillation decay and thermoluminescence characteristics. A correlation between the occurence of thermo-luminescence (TSL) peaks round RT and of very slow components in the scintillation decay of LuAG:Ce 3+ is revealed. Importance of understanding of the nature of such TSL active trapping states and their removal for further optimisation of LuAG:Ce 3+ scintillator is concluded.The experimental apparate used for scintillation and TSL measurements are described elsewhere [3,4]. We have grown YAP:Ce and LuAG:Ce crystals by Czochralski method. For scintillation decay measurements part of the grown ingot was used with polished front faces (about 1 30 Â 15 mm), while for the other measurements polished plates about 1 8 Â 1 mm were prepared. The composition was checked by electron beam excited X-ray analysis, which confirmed the appropriate stoichiometry of the perovskite and garnet phases, respectively. The concentration of Ce ions in the crystals was measured by the same method to be of about 7000 ppm and comparable amount of Ce 3+ centres in both materials were evidenced also from the optical absorption measurements (amplitude of the Ce 3+ -related absorption bands in UV-visible spectral region). The absorption spectrum of LuAG:Ce 3+ features wide Ce 3+ absorption bands around 450, 343 and 217 nm. The lowest Ce 3+ absorption bands coincide with the excitation bands (450 nm and 345 nm) of the Ce 3+ emission peaking round 510±550 nm at room temperature (RT) with the characteristic double peak structure (512 nm and 547 nm) due to the splitting of the Ce 3+ 4f ground state. The same emission appears also under X-ray excitation , see Fig. 1. The same experimental conditions of the radioluminescence measurements in Fig. 1 allowed to compare relative light output in both materials. After ...