Entrapped Molecule‐Like Europium‐Oxide Clusters in Zinc Oxide with Nearly Unaffected Host Structure. Issue 1 (20th November 2022)

• Record Type: Journal Article
• Authors: Mukherjee, Soham; Katea, Sarmad Naim; Rodrigues, Emille M.; Segre, Carlo. U.; Hemmer, Eva; Broqvist, Peter; Rensmo, Håkan; Westin, Gunnar
• Is Part Of: Small. Volume 19:Issue 1(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-11-20
• Subjects: density functional theory (DFT) -- dopant structures -- doped ZnO -- extended X‐ray absorption fine structure (EXAFS) -- lanthanide doping -- solution processing -- sponges; Nanotechnology -- Periodicals; Nanoparticles -- Periodicals; Microtechnology -- Periodicals; 620.5
• DOI: 10.1002/smll.202203331
• Languages: English
• ISSNs: 1613-6810

Abstract

Abstract: Nanocrystalline ZnO sponges doped with 5 mol% EuO1.5 are obtained by heating metal–salt complex based precursor pastes at 200–900 °C for 3 min. X‐ray diffraction, transmission electron microscopy, and extended X‐ray absorption fine structure (EXAFS) show that phase separation into ZnO:Eu and c ‐Eu2 O3 takes place upon heating at 700 °C or higher. The unit cell of the clean oxide made at 600 °C shows only ≈0.4% volume increase versus undoped ZnO, and EXAFS shows a ZnO local structure that is little affected by the Eu‐doping and an average Eu 3+ ion coordination number of ≈5.2. Comparisons of 23 density functional theory‐generated structures having differently sized Eu‐oxide clusters embedded in ZnO identify three structures with four or eight Eu atoms as the most energetically favorable. These clusters exhibit the smallest volume increase compared to undoped ZnO and Eu coordination numbers of 5.2–5.5, all in excellent agreement with experimental data. ZnO defect states are crucial for efficient Eu 3+ excitation, while c ‐Eu2 O3 phase separation results in loss of the characteristic Eu 3+ photoluminescence. The formation of molecule‐like Eu‐oxide clusters, entrapped in ZnO, proposed here, may help in understanding the nature of the unexpected high doping levels of lanthanide ions in ZnO that occur virtually without significant change in ZnO unit cell dimensions. Abstract : Eu‐oxide cluster inclusions in ZnO explain the almost retained ZnO unit‐cell dimensions observed upon doping with large, aliovalent Eu 3+ ions.