Producing LEDs from Food Waste - An Interview with Professor Prashant Sarswat

Interview conducted by Jake WilkinsonNov 5 2015

A research team at the University of Utah recently developed a method for the synthesis of quantum dot LEDS from food waste. AZoOptics talked to lead researcher, Professor Prashant K Sarswat, about the technology behind this breakthrough, quantum light production and the future of LEDs.

JW: Firstly, please could you tell our readers about your research at the University of Utah and why you think it’s important?

PKS: My research at the University of Utah is focused on electronic and optical materials processing in areas such as solar cells, light emitting diodes (LEDs), solar hydrogen production and sensing technology. My goal in most of my research is to identify low cost and innovative solutions.

Recently my team developed a method to sustainably produce LEDs from food waste, which doesn't have the negative environmental impact that producing conventional heavy metal LEDs does. Our method produced carbon dots (CDs), a form of quantum dots (QDs), to be used as LEDs.

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LEDs themselves are a durable, efficient and long lasting light source; but we need to reduce their cost of production.

I am also researching photovoltaic (PV) solar energy and hydrogen production using solar power driven photoelectrochemical (PEC) water splitting. These are two examples of clean technologies that can be used for environmentally friendly power generation.

JW: Why is there a drive to switch to using LEDs instead of incandescent and fluorescent bulbs, how do they operate differently?

PKS: I think the performance, service life, and solid state nature of LEDs are key points for this drive. LED technology is different from incandescent light bulbs and fluorescent tubes in terms of how they emit light because the physics principles behind them are different.

Incandescent light bulbs use a resistive filament to convert electrical energy into photons. Most of these bulbs have a short life.

In the case of fluorescent tubes (or bulbs) a phosphor coating on the inside of the glass housing is used to glow in the presence of an ionized gas, which is created by the current. Fluorescent bulbs have a longer service life than incandescent bulbs.

LEDs work by the phenomenon of electroluminescence. Electroluminescence can be understood as the emission of light from a semiconductor which is under the influence of an electric field. In many cases phosphor based LEDs can also be used which contain a primary source of blue or ultraviolet LEDs alongside a coating of a phosphor to produce the desired colour.

Some of the recent research reports suggest that C-dots display colour-switchable electroluminescence and also have a high colour rendering index which makes them desirable materials for LED production.

What are Quantum Dots - NIBIB | YouTube

JW: Why is the use of quantum dots in LEDs desirable? What behaviour do they display that makes them better than conventional LEDs?

PKS: Quantum-dot-based LEDs (or QDLEDs) are a relatively new member of the LED family. Quantum dots offer size dependent colour emission, i.e. the size of the quantum dot crystal determines the wavelength of light they emit when under the influence of an electric field.

This relationship enables more control over the display colour quality as specific wavelengths can be accurately selected. Some of the advantages of using QDLEDs are: the tunability of emission wavelengths, a high colour purity, and good durability and flexibility. An improved colour gamut is one of the driving factors for research in QDLEDs.

JW: What is the conventional method for making quantum and carbon dots?

PKS: Some of the methods for quantum dots production are colloidal, electrochemical and plasma assisted methods of synthesis. In most cases, the formation of carbon dots occurs through the rapid agglomeration of carbon containing material. The carbon material itself is produced by either pyrolysis, decomposition, microwave treatment or the hydrothermal treatment of small organic molecules.

JW: Please could you talk us through how you manufacture carbon dots from food waste?

PKS: The process of manufacturing carbon dots (CDs) from waste is not much different from the production of CDs from other carbonaceous sources using a solvothermal method.

In the case of producing CDs from food waste, we have to apply few additional steps such as the sorting and cleaning of the waste and the reduction of its size.

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JW: In your press release you stated that soft drink waste was the best raw material to produce carbon dots with, why is this the case?

PKS: Soft drink waste contains carbon precursors in a dissolved form. As they are dissolved it is easier to process them. In this case issues such as filtering, sorting and cleaning are not as challenging.

JW: What kind of applications can you see your carbon dot LEDs being used in?

PKS: This is a new technology and we still need to do a performance comparison between our LEDs and LEDs available on the market. Such a comparison will give us some insight into their appropriate applications.

JW: Do your carbon dot LEDs perform as well as cadmium selenide (heavy metal) LEDs? Can you achieve a high spectral range using your method?

PKS: Cadmium selenide based display technology is well-established. In contrast, carbon dots are relatively new in the family of luminescent materials.  This makes it difficult to definitively say anything until we long term research is performed.

Researchers have achieved all three primary colours of luminescence using carbon dots. This suggests that achieving a wide spectral range using our method will not be challenging.

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JW: Can you see your method of LED production being taken up on an industrial scale?

PKS: Its a little bit too premature to predict. However, the way research is growing in this area, I feel strongly that this research will be commercialized.

JW: Do your team have more research in the pipeline? Where can our readers find out about it?

PKS: We are working in various aspects of improving for this technology as well as their end use. The readers can go through our department webpage for more information.

About Professor Prashant K. Sarswat

Prashant K Sarswat is a Research Assistant Professor in the Department of Metallurgical Engineering at the University of Utah.

His primary research is in the area of photovoltaics and electronic materials processing.