Converting two low-energy photons into a single higher-energy photon is of significant importance in many fields. In medical imaging, photon up-conversion is used for imaging scattered specimens, while in photovoltaic devices it could be used to harvest photons with energies lower than the bandgap of the absorber.
Currently available systems, based on rare-earth-doped dielectrics, and organic materials are limited in both tunability and absorption cross-section. In fact, no known up-conversion systems operate on photons in the 1000-1500 nm range.
Stable inorganic nanocrystalline up-conversion systems designed at the Weizmann Institute of Science provide broad tunability of both the absorption edge and the luminescence color. These materials have the potential to be utilized in applications such as high-energy photon sources, photovoltaics and IR detection.
- Easy to manufacture
- Robust systems
- Operation at room temperature
- Photon sources
- IR detectors
The new up-conversion systems are based on a novel design comprising a compound semiconductor nanocrystal, which incorporates two quantum dots with different bandgaps separated by a tunneling barrier. The expected up-conversion mechanism occurs by the sequential absorption of two photons. The first photon excites an electronhole pair by interband absorption in the lower-energy core, resulting in a confined hole and a relatively delocalized electron. The second absorbed photon leads to further excitation of the hole, allowing it to cross the barrier layer. This, in turn, is followed by radiative recombination with the delocalized electron.