Quantum dot blinking - a problem solved?

June 16, 2015 // By Paul Buckley
Researchers at the University of Chicago have been probing the mysterious blinking process in silicon quantum dots using computer simulations at the Department of Energy’s National Energy Research Scientific Computing Center (NERSC).

The results, published in the February 28 issue of Nanoscale, may bring scientists a step closer to understanding - and possibly remediating - the problem known as 'fluorescence intermittency'.  Lasers and logic gates will not work well with variable light sources. Quantum dots can absorb specific colors of light, too, but using them to harvest sunlight in photovoltaics is not yet efficient, due in part to the mechanisms behind blinking.

Quantum dots possess some beneficial properties that their bulk counterparts lack.

Excite a quantum dot and it glows brightly in a specific color of light. Vary the width by a few atoms and you can tune it to glow different colors: The smaller the dot, the bluer the light. The larger the dot, the redder. Quantum dots can likewise be tuned to absorb specific wavelengths of light, a useful property for solar cells.

In comparison, the molecular structure of bulk semiconductors determines (and limits) the colors of light (or energies) emitted and absorbed. So, a light-emitting diode (LED) made of one material may glow green while another glows red. To get different colors, you must use different materials. Solar cells, likewise, use layers of different materials to capture various wavelengths of light.

So, why does a nanocrystal of semiconductor behave so differently than a larger lattice of the same material? In a word: size. Artificially fabricated to contain just a handful of atoms, quantum dots are so small that they exist in the twilight zone between Newtonian and quantum physics, sometimes obeying one set of rules, sometimes the other, often to surprising effect.