Introduction
Quantum dots (QDs) are a kind of nano-level semiconductors and one of the most ideal materials for displayer. By applying a certain electric field or light pressure to QDs semiconductor, they will emit light with specific frequency which will change with the size of the semiconductor. So by adjusting the size of semiconductor can control the color of the light. In the past five years, quantum dots-enhanced liquid-crystal-display (QD-LCD) has been rapidly gaining market share, and high-performance quantum dots-based light-emitting-diodes (QLEDs) are widely accepted as the next-generation technology for display.
Figure 1. Comparison of regular LCD and QD-LCD.
Mechanism
At present, inorganic phosphors, organic dyes, and QDs are the luminescence materials in commercial display products. Among them, luminescence of QDs resembles excitonic emission of bulk semiconductors. The light-emitting properties of quantum dots are caused by the interaction of electrons, holes and their surrounding environment. When the excitation energy level exceeds the band gap, the quantum dots will absorb photons to make the electrons transition from the valence band to the conduction band. The most important is that ultraviolet-visible spectrum of quantum dots has much energy level states and the first visible peak is called the quantum confinement peak, which is generated by the excitation of the lowest energy level state. Many electronic states exist at higher energy levels, thus allowing a single wavelength of light to simultaneously excite multi-color quantum dots.[1]
Figure 2. Emission mechanism of QDs.
Advantages
Compared with regular LCD, QD-LCD has the following advantages:
- The first key advantage of QDs for display applications is that emission color of QDs can be tuned in a large optical window.
- The second key advantage is that their emission color exceptionally pure and stable under intensive photo-irradiation and heating.
- The third key advantage is that QD-LCD has low processing cost and can compatible with diverse chemical media.
Key Metrics
There are three key metrics of QD-LCD as follows:
The purity of a primary color depends on the emitters used for each channel. The purest colors would be the emitters with single wavelength, corresponding to the points on the edge of a color space. Therefore, emitting materials with narrow and precisely-tuned emission peaks are favorable for wide color gamut display.
Requirements of brightness depend on viewing distance of a display and environmental lighting. Nevertheless, it is critical for luminescence materials to provide predictable, stable, and a decent range of brightness level for the devices.
Though different display devices require different operational lifetime, several thousands of hours in operation are minimum. Processing and device structures have a lot to do for operational lifetime.
What Can Alfa Chemistry Do?
Alfa Chemistry's technical R&D team has focused on the preparation and application of QDs for many years, which has established long-term cooperative relationships with many well-known enterprises and research institutions. We have conducted research on various problems encountered by displayer, which can select the appropriate solution according to the customer's experimental purpose. If you want to know more about our products, please contact us.
Reference
- Shu Y.; et al. Quantum dots for display applications. Angew. Chem. Int. Ed., 2020, 59(50): 22312-22323.
