Cadmium Free Quantum Dots

Nanoco’s core technology revolves around the commercial scale production of high quality, cadmium and heavy-metal free quantum dots, called CFQD® quantum dots, in a consistent and cost effective manner.

What are Quantum Dots and CFQD® quantum dots?

Quantum dots are fluorescent semiconductor nanoparticles typically between 10 to 100 atoms in diameter, which is about 1/1000th the width of a human hair.

When one of these particles is excited by an external light source, it absorbs the energy and re-emits the light in a different colour depending on the size of the particle. Therefore, by tuning the size of these particles, one is able to control the colour of light emitted to any colour in the spectrum.

Quantum dots are energy efficient, bright and versatile, making it a true platform technology with applications spanning from LCD displays, lighting to biomedical applications. Moreover, Nanoco’s innovative technology allows for the manufacture of highly efficient quantum dots that are completely cadmium and heavy-metal free.

Why heavy-metal and cadmium-free?

With increased awareness of the harmful effects of toxic heavy-metals, their use in consumer products is becoming increasingly regulated.

For example, the European Union Directive 2011/65/EU “Restriction of the use of certain Hazardous Substances” (RoHS), limits the amount of cadmium, lead and mercury (as well as hexavalent chromium, polybrominated biphenyl and polybrominated diphenyl ether) that can be used in electrical and electronic equipment, to protect the consumer and the environment from the effects of heavy-metal toxicity. The use of cadmium, a proven carcinogen with toxicity (LD50) of 100 – 300 mg/kg,1 is restricted ten-fold more than other RoHS regulated substances. Legislation similar to RoHS is being adopted across the globe.

Nanoco’s CFQD quantum dots, free of cadmium and other regulated heavy-metals, provide an alternative to heavy-metal based quantum dots, which can be incorporated into electrical and electronic equipment, such as displays and lighting, to produce RoHS compliant products.

1LD50 in rats and mice, oral; Health Protection Agency, Cadmium Toxicological Overview, 2010

How are they produced?

Nanoco’s patented molecular seeding process provides a reproducible route to the production of high quality quantum dots in large volumes. The process utilises molecules of a molecular cluster compound as the nucleation sites for nanoparticle growth, thus avoiding the need for a high temperature injection step.

Particle growth is maintained by the periodic addition of precursors at moderate temperatures until the desired particle size is reached. This inherent control in the process offers ease of scaling up for large volume manufacture, providing the best, most reliable route for the production of CFQD® quantum dots.

This is in contrast to a common alternative production method of quantum dots referred to as “high temperature dual injection”. In this process, the nanoparticle growth is initiated by rapidly injecting a cooler precursor solution into a warmer precursor solution above a critical temperature. The resultant cooling of the solution prevents further nucleation, with particle growth proceeding at a lower temperature.

This is a simple process for the preparation of cadmium-based quantum dots on a lab-bench scale. However, this method is challenging to scale up to achieve commercial volumes.

Nanoco’s molecular seeding process is not limited to the production of CFQD® quantum dots. Though not recommended due to the high toxicity of cadmium, the process can also be used to synthesise kilogram batches of high quality cadmium-based quantum dots in just a few hours.