Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Quantum dots brighten the future of lighting

With the age of the incandescent light bulb fading rapidly, the holy grail of the lighting industry is to develop a highly efficient form of solid-state lighting that produces high quality white light.

One of the few alternative technologies that produce pure white light is white-light quantum dots. These are ultra-small fluorescent beads of cadmium selenide that can convert the blue light produced by an LED into a warm white light with a spectrum similar tothat of incandescent light. (By contrast, compact fluorescent tubes and most white-light LEDs emit a combination of monochromatic colors that simulate white light).

Seven years ago, when white-light quantum dots were discovered accidentally in a Vanderbilt chemistry lab, their efficiency was too low for commercial applications and several experts predicted that it would be impossible to raise it to practical levels. Today, however, Vanderbilt researchers have proven those predictions wrong by reporting that they have successfully boosted the fluorescent efficiency ofthese nanocrystals from an original level of three percent to as high as 45 percent.

Potential commercial applications

“Forty-five percent is as high as the efficiency of some commercial phosphors which suggests that white-light quantum dots can now be used in some special lighting applications,” said Sandra Rosenthal, the Jack and Pamela Egan Chair of Chemistry, who directed the research which is described online in the Journal of the American Chemical Society. “The fact that we have successfully boosted their efficiency by more than 10 times also means that it should be possible to improve their efficiency even further.”

The general measure for the overall efficiency of lighting devices is called luminous efficiency and itmeasures the amount of visible light (lumens) a device produces per watt. An incandescent light bulb produces about 15 lumens/watt, while a fluorescent tubes put out about 100 lumens/watt. White light LEDs currently on the market range from 28 to 93 lumens/watt.

“We calculate that if you combine our enhanced quantum dots with the most efficient ultraviolet LED, the hybrid device would have a luminous efficiency of about 40 lumens/watt,” reportedJames McBride, research assistant professor of chemistry who has been involved in the research from its inception. “There is lots of room to improve the efficiency of UV LEDS and the improvements would translate directly into a higher efficiencies in the hybrid.”

An accidental discovery

Quantum dots were discovered in 1980. They are beads of semiconductor material – the stuff from whichtransistors are made – that are so small that they have unique electronic properties, intermediate between those of bulk semiconductors and individual molecules. One of their useful properties is fluorescence that produces distinctive colors determined by the size of the particles. As the nanocrystal’s size shrinks the light it emits shifts from red to blue. The Vanderbilt discovery was that ultra-small quantum dots, containing only 60 to 70 atoms, emit white instead of monochromatic light.

“These quantum dots are so small that almost all of the atoms are on the surface, so the white-light emission is intrinsically a surface phenomena,” said Rosenthal.

One of the first methods various groups used in the attempt to brighten the nanocrystals was “shelling” – growing a shell around them made of a different material, like zinc sulfide. Unfortunately, the shells extinguished the white light effect and the shelled quantum dots produced only colored light.

Chemists followed their noses

Following a lead from some research done at the University of North Carolina, the researchers decided to see if treating the quantum dots with metal salts would have a brightening effect. They noticed that some of the salts seemed to produce a small – 10 to 20 percent – but noticeable improvement.

“They were acetate salts and they smelled a bit like acetic acid,” said McBride. “We knew that acetic acid binds to the quantum dots so we decided to give it a try.”

The decision to follow their nose proved to be fortunate. The acetic acid treatment bumped up the quantum dots fluorescent efficiency from eight percent to 20 percent!

Acetic acid is a member of the carbocyclic acid family. So the researchers tried the other members in the family. They found that the simplest and most acidic member – formic acid, the chemical that ants use to mark their paths – worked the best, pushing the efficiency as high as 45 percent.

The brightness boost had an unexpected side effect. It shifted the peak of the color spectrum of the quantum dots slightly into the blue. This is ironic because the major complaint of white-light LEDs is that the light they produce has an unpleasant blue tint. However, the researchers maintain that they know how to correct the color-balance of the boosted light.

The researchers’ next step is to test different methods for encapsulating the enhanced quantum dots.

Other contributors to the study include graduate students Teresa E. Rosson, Sarah M. Claiborne and undergraduate research student Benjamin Stratton, who is now at Columbia University.

The work was supported by a grant from the National Science Foundation.
Read the 2005 story about the original discovery: Quantum dots that produce white light could be the light bulb’s successor

Visit Research News @ Vanderbilt for more research news from Vanderbilt. [Media Note: Vanderbilt has a 24/7 TV and radio studio with a dedicated fiber optic line and ISDN line. Use of the TV studio with Vanderbilt experts is free, except for reserving fiber time.]

David F. Salisbury | Vanderbilt University
Further information:

More articles from Physics and Astronomy:

nachricht Move over, lasers: Scientists can now create holograms from neutrons, too
21.10.2016 | National Institute of Standards and Technology (NIST)

nachricht Finding the lightest superdeformed triaxial atomic nucleus
20.10.2016 | The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

Im Focus: New Products - Highlights of COMPAMED 2016

COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.

In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...

Im Focus: Ultra-thin ferroelectric material for next-generation electronics

'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.

Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Resolving the mystery of preeclampsia

21.10.2016 | Health and Medicine

Stanford researchers create new special-purpose computer that may someday save us billions

21.10.2016 | Information Technology

From ancient fossils to future cars

21.10.2016 | Materials Sciences

More VideoLinks >>>