2013-06-12

Quantum Dot LEDs

The potential of organic LEDs shines brightly compared to the inorganic variety; QD LEDs may put them both in the shade.

Quantum dot LEDs have come up in discussion here on All LED Lighting. Blogger Blaine Bateman pointed us to a company called QD Vision, which believes that QD LEDs are the future of both display and lighting. Blogger Ron Lenk replied that they may be a future, if not the future, and promised to flesh out the details in a future blog post here.

Until we get that deeper dive, I thought a quick introduction to quantum-dot LEDs might be in order.

Quantum dots are nanoparticles, often consisting of cadmium selenide (CdSe). When an electron and a hole meet and recombine in a quantum dot, a photon is emitted. The precise frequency depends on the size of the quantum dot: For CdSe quantum-dot light, emission can be tuned from red for a dot 5nm in diameter to violet for a 1.5nm dot. QD LEDs can be manufactured by sandwiching a layer of a medium rich in quantum dots between layers that act as sources of electrons and of holes.

Quantum dots promise light sources that generate pure colors more efficiently than LEDs or OLEDs, that work at low voltage, that are cheap to manufacture, and that can eventually employ flexible, transparent, and ultra-thin form factors. QD LED technology, and its potential commercialization, is less mature than OLEDs, and inorganic LEDs are the farthest along of all.

Active research
The research scene for QD LEDs is lively. MIT is one locus of this research; in fact the founders of the aforementioned QD Vision came out of one of its laboratories. In April, workers from MIT and QD Vision published research boasting the highest efficiency yet observed for producing light from quantum dots -- approaching the theoretical maximum efficiency for this process. (Here is the abstract in Nature Photonics.)

Another of the co-authors on that paper published work in May elaborating a method of determining whether the spectral width of the light emitted by a given batch of QD nanoparticles in colloidal suspension was caused by different particles in the batch having slightly different colors, or whether each particle's emissions had a wider spectrum. The result: individual cadmium selenide particles do indeed produce very pure colors. Their new technique will allow the fine-tuning of production processes for QD solutions. (Here is the abstract in Nature Chemistry.)

High schoolers get into the act
A student entry in Intel's International Science & Engineering Fair points a way to producing white light with any desired color temperature (video) by using QD LEDs. Jong Ho David Lee, from the Lawrenceville School in New Jersey, developed a set of quantum dots that work with blue LEDs to generate white light with a broader spectrum than those exhibited by commercial white LEDs. He demonstrated a way to tune the color temperature of white QD LED light by selecting the size of the quantum dots.

Have you had any exposure to quantum dot LEDs? Let us know in the comments about any resources you have found helpful on the subject. And we'll look forward to Ron Lenk's deeper exploration here.

— Keith Dawson , Editor-in-Chief, All LED Lighting