Quantum Dots 101: Introduction to Quantum Dots
For the past 25 years, Nanoco has been developing quantum dots (QDs) to enhance a variety of different technologies, but what exactly are they and how can they be used for such a wide range of applications? In the first of this Quantum Dots 101 series, we’ll go through some of the basics of QD technology.
QDs are nanoparticles of semiconductor material with a diameter between around 1 – 10 nm, which is about 1/10,000th the width of a human hair. This tiny size gives rise to the unique properties of QDs. At such small dimensions, the laws of classical mechanics break down, so QDs display what’s known as “size quantisation” effects, whereby their optical and electronic properties depend on the particle size. In practical terms, this means that for a given type of QD material, the way it behaves can be manipulated simply by changing its size.
When QDs are excited by an external light source, they absorb energy that they then re-emit at a longer wavelength. The larger the QDs, the longer the emission wavelength, which can be tuned from the UV, across the visible spectrum and into the infrared, simply by making QDs of different sizes and from different types of semiconductor materials.
It’s this property that’s exploited in TVs, where a blue light source is used to excite two different size populations of QDs that re-emit green and red light. The green and red QDs can be made from the same type of material, such as indium phosphide or cadmium selenide, but the red particles are bigger than the green.
The peak wavelength at which QDs absorb light is also size-tunable. This quirky property is being used to develop infrared sensors, where QDs are integrated into cameras to allow us to “see” light being reflected from objects that would usually be invisible to the naked eye.
We’ll go into more detail on how some of these applications work in future Quantum Dots 101 posts.