The colloidal synthesis of ZnO-WO 3 heteroaggregates composed of 3-5 nm particles is presented. These sols can be used to prepare nanocrystalline ZnWO 4 xerogels, powders, and thin films with strong blue fluorescence (quantum yield between 25 and 50% at room temperature). The conversion of the precursor aggregates into nano-and microcrystalline monoclinic ZnWO 4 Sanmartinite has been followed by XRD, DTA-TG-MS, SEM, FTIR, optical absorption, and fluorescence methods. The ZnWO 4 crystallites start to develop at 350 °C, and their mean crystal size increases with temperature to 35 nm at 400 °C and 120 nm at 600 °C. At the same time, the fluorescence intensity increases by 3 orders of magnitude within the aforementioned temperature regime, no matter whether X-rays or UV photons are used to excite the samples. In complementary time-resolved X-ray fluorescence investigations, two recombination processes in the micro-and millisecond range were detected. In weakly fluorescing ZnO-WO 3 aggregate samples at sizes between 10 and 30 nm, the slow millisecond process dominates the recombination of the charge carriers whereas in 50-275 nm crystals and above, the faster 2.5 µs process dominates the decay kinetics. Accordingly, the slow afterglow process is attributed to a recombination between electrons and holes deeply trapped at the surface of the heteroaggregates. The faster 2.5 µs recombination process takes place only in the perfectly developed Sanmartinite phase.

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1998 luminescence, fluorescence luminescence, fluorescence (solids and liquids) D 6540 -016Conversion of Colloidal ZnO-WO 3 Heteroaggregates into Strongly Blue Luminescing ZnWO 4 Xerogels and Films.-ZnO-WO 3 heteroaggregates are prepared from Zn 4 O(OAc) 6 and W(OMe) 6 . In a second step ZnWO 4 xerogels and films are prepared by annealing at 300-500 • C. The ZnWO 4 has a monoclinic Sanmartinite structure determined by powder XRD. The blue emission is activated during the thermal conversion of ZnO-WO 3 sandwich structures into the nanocrystalline ZnWO 4 sanmartinite phase. The electronic correlation diagram before and after the thermal conversion into ZnWO 4 shows the different band gaps for photo-and X-ray-luminescence processes. -(BONANNI, M.; SPANHEL, L.; LERCH, M.; FUEGLEIN, E.; MUELLER, G.; JERMANN, F.; Chem. Mater. 10 (1998) 1, 304-310; Lehrstuhl Silicatchem., Julius-Maximilians-Univ.,