Steven Hughes, Roanoke College – Improving LED Technology

On Roanoke College Week: LED bulbs reduce energy consumption; but can they get better?

Steven Hughes, assistant professor of chemistry, examines this question.

Dr. Steven Hughes, assistant professor of chemistry, teaches general and physical chemistry. He has a strong research interest in finding new materials systems for LED lighting that exhibit sufficient light shifting properties while also avoiding the use of toxic metals such as cadmium or lead.

Improving LED Technology

How can we make lighting our lives more energy and cost efficient? Keeping our homes and workplaces bright now accounts for approximately 20% of all our energy consumption. By replacing standard incandescent bulbs with commercially available LED bulbs, one can improve household lighting efficiency by 600%.  Yet there is still plenty of room to continue improving LED technology.

Take the phosphor- a phosphor is a substance that helps convert the harsh, blue light from bare LEDs into warmer wavelengths that are easier on the eyes. But traditional phosphors are expensive and tend to absorb LED blue light poorly. Because of this, there has been a push to replace these materials with semiconductor nanocrystals. 

Nanocrystals are tiny crystalline particles with a variety of uses. In the world of LED lights, they are a potentially a more cost-effective way to strongly absorb the blue light – in fact, some of these materials are being used in commercial televisions and tablets.

Unfortunately, the nanocrystals currently being used for these applications are cadmium based.  Cadmium is toxic, and its use has become heavily regulated both in the United States and internationally.  As a result, the industry is looking for cadmium free replacements. 

We are currently researching two semiconductor materials systems: silver gallium sulfide and copper indium sulfide.  While these are more complex chemical systems, they have some ideal properties that make them excellent candidates as LED phosphors such as ideal color and long-term stability. 

In our lab, students routinely grow these nanocrystals using high-temperature, air-free synthetic techniques.  Afterwards we measure their optical performance studying how well they both absorb light and subsequently re-emit it by fluorescence. 

Most materials in lighting are bad at what they do and use up a lot of rare earth materials. New compositions of nanocrystals can match the performance of today’s cadmium nanocrystals without the dangers posed by toxic elements.