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Quantitative Atomic-Site Analysis of Functional Dopants/Point Defects in Crystalline Materials by Electron-Channeling-Enhanced Microanalysis
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Light- and Chemical-Doping-Induced Magnetic Behavior of Eu Molecular Systems
Tijana Rajh1,2, Eric Masson3, Kyaw Zin Latt1
1Nanoscience and Technology Division, Argonne National Laboratory, 9700 S Cass Ave, Argonne, Illinois 60540, United States.
Inorganic Chemistry
|July 28, 2023
Summary
Europium (Eu) compounds can be reduced to paramagnetic Eu(II) species, affecting their luminescence. Encapsulating Eu complexes with Cucurbit[7]uril prevents this reduction, preserving luminescence properties.
Area of Science:
- Inorganic Chemistry
- Photochemistry
- Spectroscopy
Background:
- Europium (Eu) complexes are typically studied in the Eu(III) oxidation state, which is diamagnetic.
- Understanding the environmental and oxidation state effects on Eu compounds is crucial for their application in luminescence and materials science.
- Ligand-to-metal charge transfer (LMCT) is a key process that can alter the oxidation state and properties of metal complexes.
Purpose of the Study:
- To investigate the role of the environment and oxidation states of coordinated Eu compounds using variable temperature electron paramagnetic resonance (VT-EPR).
- To explore the formation of paramagnetic species through chemical reduction of Eu(III) complexes.
- To examine the impact of LMCT on the luminescence of Eu(dipic)3 and the effect of Cucurbit[7]uril encapsulation.
Main Methods:
- Variable temperature electron paramagnetic resonance (VT-EPR) spectroscopy was employed to study Eu compounds.
- Chemical reduction was used to generate paramagnetic Eu species.
- Photochemical studies involving illumination at low temperatures (4 K) were conducted on Eu(dipic)3.
- Simulation of EPR spectra was performed using two Eu isotopes (151Eu and 153Eu).
Main Results:
- Chemical reduction of Eu(III) chelating complexes yielded paramagnetic Eu species.
- EPR spectra of reduced complexes exhibited axial symmetry, simulated with 151Eu and 153Eu isotopes.
- Illumination of Eu(dipic)3 induced LMCT, forming Eu(II) in a rhombic environment and altering luminescence (reduced red, appearing blue CT).
- Encapsulation of Eu(dipic)3 with Cucurbit[7]uril inhibited LMCT and Eu(II) formation upon illumination.
Conclusions:
- Eu(III) complexes can be reduced to paramagnetic Eu(II) species, with distinct EPR signatures.
- LMCT significantly impacts the photophysical properties, specifically luminescence, of Eu complexes.
- Macrocyclic encapsulation, such as with Cucurbit[7]uril, can effectively prevent LMCT and stabilize the Eu(III) oxidation state under illumination.
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