A team of scientists have used nontoxic silicon nanocrystals to convert low-energy photons into high-energy ones. The technique could lead improvements in everything from minimally invasive photodynamic treatments for cancer; to new solar-energy conversion tech; to new approaches to quantum information.
A green lower-energy laser light goes through silicon quantum dots which upconvert it into a higher-energy blue light.
The new technique was pioneered by a team of materials scientists at the University of California, Riverside and The University of Texas at Austin.
Working together they have demonstrated that it is possible to achieve photon up-conversion. This means that a material can absorb two or more photons and then emit light at a shorter wavelength. For example, converting infrared light to visible light.
The new technique has impacts on a whole range of fields. From allowing scientists to move one step closer to developing minimally invasive photodynamic treatments for cancer to improving solar-energy conversion, quantum information, and near-infrared driven photocatalysis.
While photon up-conversion materials have been around since the 1960’s they have either used toxic materials (making them unsuitable for medical treatments) or they have not been very efficient.
This is the first time a team has used Silicon, which is not toxic, to demonstrate that silicon nanocrystals can up-convert photons.
The team made the breakthrough thanks to the work of doctoral student Pan Xia. Pan carefully studied the surface chemistry of silicon nanocrystals. The team was able to use his research to attach ligands (which help bind molecules together) to the nanoparticle to transfer the energy from the nanocrystals to surrounding molecules.
By shining a light into the solution the team found the silicon nanocrystals could transfer the energy to surrounding molecules. This process – called triplet-triplet fusion – then converts low-energy to high energy. The real-world effect is the emission of light at a shorter wavelength (or higher energy) than the light initially absorbed by the nanoparticle solution.
While the team’s upconversion yields are still fairly low (around 7%) the use of the Silicon nanocrystals is groundbreaking and represents an important step forward for the field. We look forward to seeing how the technique can now be used more widely.
Published as “Achieving spin-triplet exciton transfer between silicon and molecular acceptors for photon upconversion” in Nature Chemistry