By changing the light parameters of metal-organic frameworks (MOFs), scientists from ITMO University in Saint Petersburg, Leipzig University and Eindhoven University of Technology have managed to generate fully controllable excitons which could record information at room temperature.

An exciton provides energy transfer between photons and electrons. According to the scientific community, this mediation of quasiparticles will help to combine optics with electronics to create more compact and energy efficient equipment for rapid recording and processing an optical signal.

However, current exciton devices either operate only at low temperature or are difficult to manufacture.

MOFs have a layered structure. Between the layers, there is a physical attraction called van der Waals force. To prevent the plates from sticking together, the interlayer space is filled with an organic liquid.

In such crystals, there are two types of excitons: intralayer and interlayer. The first arise when a photon absorbed by the crystal turns into an electron-hole pair inside a layer, but the second appear when an electron and a hole belong to neighbouring layers. Both kinds of quasiparticles then disintegrate, re-radiating the energy as a photon.

The life time of intralayer excitons is short, but their high density and agility could allow them to be used to generate light in LEDs and lasers. Interlayer excitons are more stable, but slow-moving, which the researchers think could be used for data recording.

"We locally heated the crystal with a laser,” explained ITMO associate professor Valentin Milichko. “In the place of exposure, the layers stuck together and the luminescence of excitons disappeared while the rest of the crystal continued shining. This could mean that we recorded 1bit of information, and the record, in the form of a dark spot, was kept for many days.

“To delete the data, we put the MOF into the same organic liquid that supports the layers. The crystal itself is not affected, but the recorded information disappears."