Klaus Müller-Buschbaum, Martin Jansen, and co-workers have shown how the dense framework europium(II) imidazolate [EuIm₂] can form thin layers with switchable transparency. The researchers in Würzburg and Stuttgart, both Germany, chose to study the deposition of [EuIm^₂] because of its high quantum yield and thermal stability.

The team developed a new technique known as scanning femto-PLD (where PLD is pulsed laser deposition) to form films with thicknesses of 100–150 nm by using a femtosecond laser beam to ablate the material in a vacuum chamber. Further studies showed that both the crystal structure and luminescent properties of [EuIm₂] were retained in the films.

The optical properties of the films are interesting: the films are transparent under visible light, whereas they appear nontransparent under UV light. This phenomenon arises from the intrinsic emission and reflection of incident and emitted light at the particle surface.

This work brings an application of framework compounds and coordination polymers to the area of smart films and coatings.

• Highly Luminescent Thin Films of the Dense Framework ³_∞[EuIm₂] with Switchable Transparency Formed by Scanning Femtosecond-Pulse Laser Deposition,
  Dieter Fischer, Larissa V. Meyer, Martin Jansen, Klaus Müller-Buschbaum,
  Angew. Chem. Int. Ed. 2013.
  DOI: 10.1002/anie.201305648