CFQD® quantum dots are Nanoco’s core technology, consisting of 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 can also be tuned for use in a variety of different media with adjustment of the surface ligands, opening them up to several different form factors and applications.
Applications
The best of both technologies can be achieved with the addition of a quantum dot colour conversion layer on top of an OLED structure. Similar to an LCD system, the quantum dot layer absorbs excitation light from the OLED and down converts it to narrow band green and red light to achieve high colour quality performance. Due to the highly absorbing nature of the dots this effect can be achieved in a layer only a few microns thick, maintaining the thin form factor and flexibility associated with OLED devices.
With pixel level turn off control OLED displays are designed to solve one of the inherent issues with traditional LCD displays which is the ability to achieve true on screen black images. OLED displays however still struggle to reach the same richness of colour of CFQD® quantum dot-enabled screens, due to their broad emission spectra.
μLEDs are LEDs with a very small chip size (down to single digit microns) which can be directly used as pixels on a display device. Due to the viewer seeing the LEDs directly this allows for higher contrast, response times and efficiency over traditional LCD technology, and their small size and high power density opens them up for wearable applications such as smartwatches and AR/VR headsets. μLEDs, however, struggle to represent colours across the spectrum with red in particular providing a real challenge for the industry, with traditional colour conversion techniques such as phosphor being insufficient due to physical size constraints.
Due to their small size and high absorbance characteristics, CFQD® quantum dots provide an ideal solution to this issue. Similar to OLED colour conversion applications a thin layer of CFQD® quantum dots can be applied to the top emitting surface of the μLED to down convert the emission to those required for a full colour display. In addition, this technique allows for the colour conversion of blue μLEDs grown on one substrate, eliminating the need to bring multiple coloured LEDs together in an array for a display using expensive and time consuming manufacturing techniques.
The next stage of display design will be the incorporation of CFQD® quantum dots directly within the OLED emitting device, with development work currently underway at Nanoco to achieve this. These next generation devices will combine the flexibility and dynamic range of OLEDs with the superior colour performance of quantum dots without the need for an externally printed colour conversion layer.
CFQD® quantum dots provide an attractive proposition for optical security tagging. High tunability and narrow emission allow the dots to be combined to generate a complex optical fingerprint proving very difficult to imitate. Flexibility of the CFQD® quantum dots ligand system also enables them to be dispersed in ink formulations allowing for simple printing techniques to be used for application.
