Research

EMR is particularly suited to detect and microscopically identify atomic or molecular systems with unpaired electrons, these are paramagnetic centers.

The EMR group is part of the Department of Solid State Sciences of Ghent University and is mainly involved in the study of defects in solids, that are paramagnetic (have unpaired electrons) or that can be made paramagnetic by, e.g., exposure to ionizing radiation, thermal treatment, … For optimal detectability, such paramagnetic centers are present in fairly low concentrations in an otherwise diamagnetic matrix ((semi)insulating solid, a-polar liquid, gas).

The application field of EPR and related techniques is very wide. It extends far beyond (solid state) physics, and includes also chemistry (e.g. catalysis in liquid or gas phase), biochemistry and biology, geology, medicine, etc. Please take a look at the numerous illustrations of EMR applications, that we are involved in. It will become clear that not only detailed structural information can be obtained, but that also unpaired electron numbers or densities can be determined, which leads to applications in dosimetry and dating.

About EMR

EMR is the electronic counterpart of NMR (Nuclear Magnetic Resonance). EMR includes in the first place the basic technique EPR (Electron Paramagnetic Resonance), also known as ESR (Electron Spin Resonance). Derived techniques where nuclear spin transitions are detected include ENDOR (Electron Nuclear DOuble Resonance) and EIE (ENDOR induced EPR). For instance with ENDOR, NMR transitions can be observed via the EPR signal, with an inherently higher sensitivity than with NMR itself.

On the one hand, EMR allows high-level detailed characterization of paramagnetic centers, in particular

  • electron spin
  • electronic and geometrical structure, valence state
  • symmetry
  • chemical identity

Due to its high sensitivity (about 1010 paramagnetic centers in absolute terms), reproducibility and non-destructive character, EPR has also important applications in the field of

  • radiation dosimetry
  • dating
  • detection of irradiation in foodstuffs

Comparable to NMR, EMR makes use of an (electronic) magnetic moment that interacts with external or internal magnetic fields, e.g. due to neighboring nuclear spins. EMR transitions are of the magnetic dipole type and occur between electronic levels split by Zeeman and/or hyperfine interactions. They are induced by microwave radiation (mm/cm region).

Although within the UGent Department of Solid State Sciences, the research on defects and radicals in solids prevails, samples can also be glasses, polymers, liquids or even gases. For our setups typical sample dimension are a few mm3. Samples should not be electrically conducting and, in case of liquids, solvents should be a-polar.

At the moment the EMR group disposes of EPR, ENDOR and EI-EPR in X and Q-band (microwaves with frequencies around 9.5 GHz and 34 GHz, respectively), equipped with cryogenics and allowing in situ illumination.

Research topics

Over several decades, the EMR group has acquired important expertise in detecting, identifying and/or quantifying paramagnetic centers in the following systems

  • defects and radicals in apatites
  • radiation-induced defects in carbohydrates (sugars) and amino acids (e.g. alanine)
  • short-lived radicals stabilized by spin traps
  • transition metal impurities or dopants in inorganic solids
  • lanthanide activated optical materials (phosphors)
  • defects in semiconductors
  • metal-organic frameworks

At present, attention goes mostly out to optical materials, metal- and covalent organic frameworks, lead-silicate glasses and plasma-treated polymers and liquids.

Selected publications:

Identification of vanadium dopant sites in the metal-organic framework DUT-5(Al)

Kwinten Maes UGent, Lisa Martin UGent, Samira Khelifi UGent, Alexander Hoffman UGent, Karen Leus UGent, Pascal Van Der Voort UGent, Etienne Goovaerts, Philippe Smet UGent, Veronique Van Speybroeck UGent, Freddy Callens UGent, et al.

(2021) PHYSICAL CHEMISTRY CHEMICAL PHYSICS. 23(12). p.7088-7100

 

Determination of the Fe3+/ΣFe ratio in synthetic lead silicate slags using X-band CW-EPR

Vincent Cnockaert (UGent) , Inge Bellemans (UGent) , Tijl Crivits, Henk Vrielinck (UGent) , Bart Blanpain and Kim Verbeken (UGent)

(2021) JOURNAL OF SUSTAINABLE METALLURGY. 7(2). p.519-536

 

Designing photochromic materials with large luminescence modulation and strong photochromic efficiency for dual-mode rewritable optical storage

Zetian Yang (UGent) , Jiaren Du, Lisa Martin (UGent) , Ang Feng (UGent) , Ewoud Cosaert (UGent) , Bo Zhao (UGent) , Wanlu Liu (UGent) , Rik Van Deun (UGent) , Henk Vrielinck (UGent) and Dirk Poelman (UGent)

(2021) ADVANCED OPTICAL MATERIALS. 9(20).

Recent projects of the EMR group

We are part of the Benelux EPR Society and wish you a pleasant stay on our site and hope to meet you soon in our laboratories. The EMR team.