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Kocsis K, Niedermaier M, Kasparek V, Bernardi J, Redhammer G, Bockstedte M, Berger T, Diwald O. From Anhydrous Zinc Oxide Nanoparticle Powders to Aqueous Colloids: Impact of Water Condensation and Organic Salt Adsorption on Free Exciton Emission. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:8741-8747. [PMID: 31244249 PMCID: PMC7116045 DOI: 10.1021/acs.langmuir.9b00656] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Variations in the composition and structure of ZnO nanoparticle interfaces have a key influence on the materials' optoelectronic properties and are responsible for high number of discrepant results reported for ZnO-based nanomaterials. Here, we conduct a systematic study of the room-temperature photoluminescence of anhydrous ZnO nanocrystals, as synthesized in the gas phase and processed in water-free atmosphere, and of their colloidal derivatives in aqueous dispersions with varying amounts of organic salt admixtures. A free exciton band at hν = 3.3 eV is essentially absent in the anhydrous ZnO nanocrystal powders measured in vacuum or in oxygen atmosphere. Surface hydration of the nanoparticles during colloid formation leads to the emergence of the free exciton band at hν = 3.3 eV and induces a small but significant release in lattice strain as detected by X-ray diffraction. Most importantly, admixture of acetate or citrate ions to the aqueous colloidal dispersions not only allows for the control of the ζ-potential but also affects the intensity of the free exciton emission in a correlated manner. The buildup of negative charge at the solid-liquid interface, as produced by citrate adsorption, increases the free exciton emission. This effect is attributed to the suppression of electron trapping in the near-surface region, which counteracts nonradiative exciton recombination. Using well-defined ZnO nanoparticles as model systems for interface chemistry studies, our findings highlight water-induced key effects that depend on the composition of the aqueous solution shell around the semiconducting metal oxide nanoparticles.
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Affiliation(s)
- Krisztina Kocsis
- Department of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, 5020 Salzburg, Austria
| | - Matthias Niedermaier
- Department of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, 5020 Salzburg, Austria
| | - Vít Kasparek
- Central European Institute of Technology, Brno University of
Technology, Purkynova 123, 612 00 Brno, Czech Republic
| | - Johannes Bernardi
- University Service Centre for Transmission Electron
Microscopy, Technische Universität Wien, 1040 Vienna, Austria
| | - Günther Redhammer
- Department of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, 5020 Salzburg, Austria
| | - Michel Bockstedte
- Department of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, 5020 Salzburg, Austria
| | - Thomas Berger
- Department of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, 5020 Salzburg, Austria
| | - Oliver Diwald
- Department of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, 5020 Salzburg, Austria
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Kocsis K, Niedermaier M, Bernardi J, Berger T, Diwald O. Changing interfaces: Photoluminescent ZnO nanoparticle powders in different aqueous environments. SURFACE SCIENCE 2016; 652:253-260. [PMID: 32903287 PMCID: PMC7116034 DOI: 10.1016/j.susc.2016.02.019] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We transformed vapor phase grown ZnO nanoparticle powders into aqueous ZnO nanoparticle dispersions and studied the impact of associated microstructure and interface property changes on their spectroscopic properties. With photoluminescence (PL) spectroscopy, we probed oxygen interstitials O i 2 - in the near surface region and tracked their specific PL emission response at hvEM = 2.1 eV during the controlled conversion of the solid-vacuum into the solid-liquid interface. While oxygen adsorption via the gas phase does affect the intensity of the PL emission bands, the O2 contact with ZnO nanoparticles across the solid-liquid interface does not. Moreover, we found that the near band edge emission feature at hvEM = 3.2 eV gains relative intensity with regard to the PL emission features in the visible light region. Searching for potential PL indicators that are specific to early stages of particle dissolution, we addressed for aqueous ZnO nanoparticle dispersions the effect of formic acid adsorption. In the absence of related spectroscopic features, we were able to consistently track ZnO nanoparticle dissolution and the concomitant formation of sol- vated Zinc formate species by means of PL and FT-IR spectroscopy, dynamic light scattering, and zeta potential measurements. For a more consistent and robust assessment of nanoparticle properties in different continuous phases, we discuss characterization challenges and potential pitfalls that arise upon replacing the solid-gas with the solid-liquid interface.
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Affiliation(s)
- Krisztina Kocsis
- Department of Chemistry and Physics of Materials, Paris Lodron University of Salzburg, Hellbrunnerstrasse 34/III, A - 5020, Salzburg, Austria
| | - Matthias Niedermaier
- Department of Chemistry and Physics of Materials, Paris Lodron University of Salzburg, Hellbrunnerstrasse 34/III, A - 5020, Salzburg, Austria
| | - Johannes Bernardi
- University Service Center for Transmission Electron Microscopy (USTEM), TU Wien, Wiedner Hauptstrasse 8-10, A-1040 Vienna, Austria
| | - Thomas Berger
- Department of Chemistry and Physics of Materials, Paris Lodron University of Salzburg, Hellbrunnerstrasse 34/III, A - 5020, Salzburg, Austria
| | - Oliver Diwald
- Department of Chemistry and Physics of Materials, Paris Lodron University of Salzburg, Hellbrunnerstrasse 34/III, A - 5020, Salzburg, Austria
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Gheisi AR, Neygandhi C, Sternig AK, Carrasco E, Marbach H, Thomele D, Diwald O. O2 adsorption dependent photoluminescence emission from metal oxide nanoparticles. Phys Chem Chem Phys 2014; 16:23922-9. [DOI: 10.1039/c4cp03080j] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Optical properties of metal oxide nanoparticles are subject to synthesis related defects and adsorbates.
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Affiliation(s)
- Amir R. Gheisi
- Institute of Particle Technology
- Friedrich-Alexander University Erlangen-Nürnberg
- Erlangen, Germany
| | - Chris Neygandhi
- Institute of Particle Technology
- Friedrich-Alexander University Erlangen-Nürnberg
- Erlangen, Germany
| | - Andreas K. Sternig
- Institute of Particle Technology
- Friedrich-Alexander University Erlangen-Nürnberg
- Erlangen, Germany
| | - Esther Carrasco
- Lehrstuhl für Physikalische Chemie II
- Friedrich-Alexander University Erlangen-Nürnberg
- Erlangen, Germany
| | - Hubertus Marbach
- Lehrstuhl für Physikalische Chemie II
- Friedrich-Alexander University Erlangen-Nürnberg
- Erlangen, Germany
| | - Daniel Thomele
- Department of Materials Science & Physics
- Paris-Lodron University of Salzburg
- Salzburg, Austria
| | - Oliver Diwald
- Department of Materials Science & Physics
- Paris-Lodron University of Salzburg
- Salzburg, Austria
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Sternig A, Stankic S, Müller M, Siedl N, Diwald O. Surface exciton separation in photoexcited MgO nanocube powders. NANOSCALE 2012; 4:7494-7500. [PMID: 23100068 DOI: 10.1039/c2nr31844j] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
In MgO nanocube powders surface excitons can separate and the resulting charge carriers provide reactive adsorption sites at well-defined surface elements. We employed photoluminescence (PL) emission bands originating from the photoexcitation of nanocube corners and edges as quantitative probes to explore their chemical reactivity towards molecular hydrogen. Surface excitons which form at corners and edges exhibit similar cross-sections for separation in vacuum. The separation of edge excitons, however, is significantly enhanced in hydrogen atmosphere when hydrogen adsorption occurs as a simultaneous surface process. The electronic structure of MgO nanocube edges which split hydrogen heterolytically upon generation of surface hydroxyls and hydrides is unaffected by the photoexcitation of corners. Respective edges, however, are efficient absorption sites for UV photons. Transfer of exciton energy to oxygen ions in corners is followed by exciton separation which transforms corner ions into surface radicals leading to a well-defined starting point for the site selective functionalization of metal oxide nanostructures.
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Affiliation(s)
- Andreas Sternig
- Cluster of Excellence - Engineering of Advanced Materials (EAM), Friedrich-Alexander University Erlangen-Nuremberg, Cauerstrasse 4, 91058 Erlangen, Germany
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