Conversion of Colloidal ZnO−WO3 Heteroaggregates into Strongly Blue Luminescing ZnWO4 Xerogels and Films
The colloidal synthesis of ZnO−WO3 heteroaggregates composed of 3−5 nm particles is presented. These sols can be used to prepare nanocrystalline ZnWO4 xerogels, powders, and thin films with strong blue fluorescence (quantum yield between 25 and 50% at room temperature). The conversion of the precurs...
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Published in | Chemistry of materials Vol. 10; no. 1; pp. 304 - 310 |
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Main Authors | , , , , , |
Format | Journal Article |
Language | English |
Published |
Washington, DC
American Chemical Society
19.01.1998
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Subjects | |
Online Access | Get full text |
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Summary: | The colloidal synthesis of ZnO−WO3 heteroaggregates composed of 3−5 nm particles is presented. These sols can be used to prepare nanocrystalline ZnWO4 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 ZnWO4 Sanmartinite has been followed by XRD, DTA−TG−MS, SEM, FTIR, optical absorption, and fluorescence methods. The ZnWO4 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−WO3 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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Bibliography: | Abstract published in Advance ACS Abstracts, November 15, 1997. ark:/67375/TPS-PJK5VHMP-V istex:978187C540C3B3594F018AAC97F2CEBAB6126E75 |
ISSN: | 0897-4756 1520-5002 |
DOI: | 10.1021/cm9704591 |