Link between Structural and Optical Properties of CoxFe3-xO4Nanoparticles and Thin Films with Different Co/Fe Ratios

Kampermann, L. and Klein, J. and Korte, J. and Kowollik, O. and Pfingsten, O. and Smola, T. and Saddeler, S. and Piotrowiak, T.H. and Salamon, S. and Landers, J. and Wende, H. and Ludwig, A. and Schulz, S. and Bacher, G.

Volume: 125 Pages: 14356-14365
DOI: 10.1021/acs.jpcc.0c11277
Published: 2021

CoxFe3-xO4nanoparticles (x= 0.4 tox= 2.5) and thin films (x= 0.9 tox= 2.2) are analyzed by Raman, absorption, and photoluminescence spectroscopy to link structural and optical properties to different cobalt to iron (Co/Fe) ratios. Raman spectroscopy shows that with decreasing Co content, the crystal structure changes from a predominantly normal cubic spinel phase to a mixed inverse spinel phase. This finding is supported by absorption spectroscopy that points out that inter valence charge transfer (IVCT) processes between octahedrally coordinated Co2+and Fe3+cations become more prominent with increasing Fe content. Independent of the Co/Fe ratio, CoxFe3-xO4nanoparticles show a broad photoluminescence (PL) band with a maximum at around 510 nm. Time-resolved photoluminescence spectroscopy shows subnanosecond lifetimes and temperature-resolved photoluminescence experiments reveal that the green PL increases with decreasing temperature (300 to 10 K) while showing no temperature-dependent shift in energy. It is proposed that this green PL originates from OH-groups on the particles’ surface. © 2021 The Authors. Published by American Chemical Society

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