Impurities Held Back Quantum Dot Production Method
Quantum dots are nanoscale semiconducting crystals sometimes also referred to as designer molecules. All semiconductors will have electrons excited by certain frequencies of light, and also give off certain frequencies of light if there is enough energy available. This is key to both LEDs and photovoltaics. What the frequencies of light are though will differ from material to material. Quantum dots on the other hand can be made to respond to whatever frequency someone wants; only production techniques stand in the way.
This makes them very interesting to every field that deals with both electronics and optics. Unfortunately creating them is not always very easy, and one method that, on paper, looked promising was not performing as people wanted. Now researchers at Berkeley Lab have figured out why, by accident.
While cleaning out the lab, a researcher checked the luminescence of a sample of quantum dots that was ix months hold. To his surprise it was responding seven times stronger than when it was freshly made. Already that is a large improvement, but why? To figure it out the researcher heated the sample to 100 C, to accelerate whatever happened during those six months. The result was a 400-fold increase in just 30 hours and an explanation.
The production method used is solution-based as opposed to the traditional colloid-based technique. This was leaving behind cations though which were blocking the movement of charge carriers. Heat causes the impurities to leave the sample, and thus boost the luminescence. Perhaps we will be seeing quantum dot displays and solar panels sooner than we thought.