Quantum dots (QD) technology is transforming the lighting and display industries. A popular talking point in nanotechnology and materials science, these semiconductor nanocrystals are really small semiconductor particles, as small as a few nanometers in size.
Their electronics and optical properties fall between bulk discrete atoms and semiconductors. These properties are actually dependent on both the size and shape of these QDs. For instance, larger quantum dots of 5–6 nm size emit longer wavelengths in comparison to shorter wavelengths emitted by smaller QDs of size 2–3 nm. Also, the former QDs yield orange or red colors, while the latter one does blue and green. The specificity of these colors, however, depends on the composition of the quantum dots.
QDs are nanoscale semiconductor materials with tightly confined electrons or electron holes, much like a 3D particle in a box model. By coupling two or more of these QDs, an artificial molecule can also be created. Meanwhile, precisely assembling them can form superlattices acting as artificial solid-state materials whose unique optical and electronic properties can be controlled.
Just last year, Moungi G. Bawendi, Alexei I. Ekimov, and Louis E. Brus were awarded the Nobel Prize in Chemistry for the discovery and development of quantum dots. However, QDs are not as young as technology. They were first discovered many decades ago, in 1980, and it’s been years since QDs have been in use in LCDs as remote phosphors.
The potential application of quantum dots is not limited to displays, either. They further extend to LEDs, lasers, solar cells, single-photon sources, single-electron transistors, microscopy, bioimaging, cell biology research, and chemical reaction catalysis.
Driven by the increasing demand for energy-efficient lighting solutions and high-quality display devices across various industries, the QD market is projected to see impressive growth at a CAGR of 17.40% in the coming years. The global market size of QD is projected to reach $12.34 bln before the end of this decade.
Given their wide application and expected market size growth, quantum dots have been the subject of much research and experimentation. However, this has been mainly in the visible spectrum. This means there is a lot to be discovered about the technology in ultraviolet and infrared regions.
Infrared technology has many use cases, so there is an increasing requirement for cost-effective, easy-to-develop, and easy-to-use optoelectronic materials that are tunable and infrared-active. This has led to the development of infrared quantum dots. Due to the quantum confinement effect, the band gaps of infrared quantum dots can be tuned whenever needed simply through dimensional constraints.
Progress in the development of infrared quantum dots as infrared absorbers, such as in solar fuels and photovoltaics, and infrared light emitters, like in biological imaging and light-emitting diodes, is facilitating the implementation of QDs into emerging applications.
Click here for a list of the top five companies leading the development of nanotechnology.
Developing High-quality Nanocrystals
Now, Andrew Smith, a bioengineering professor at the University of Illinois at Urbana-Champaign, and postdoc researcher Wonseok Lee have developed new high-quality nanocrystal products.
Published in Nature Synthesis and funded by the National Institutes of Health and the National Science Foundation, the research was the first instance of infrared QDs having the same high standards as those in the visible light spectrum.
Even after nearly half a century of nanocrystal technology’s existence, we have only seen advancement in nanocrystals operating in the visible portion of the spectrum. This makes sense, given that they are a “big part of display devices.”
As Smith shared, the biggest part of any technology is light emitting or absorbing. So, the focus has been on developing a technology with the biggest market today.
But this is not all. Besides the visible spectrum nanocrystals having much higher demand, the chemistry of the materials used in the infrared is also harder. This includes lower energy and longer wavelengths than light in the visible spectrum.
Now, accomplishing light emission and absorption in the infrared requires heavier elements whose chemistry is difficult. This means less predictable reactions and more undesired side reactions.
This isn’t even the end of it. These heavier elements are further prone to degradation. They are even susceptible to ambient changes in the environment, such as water.
When it comes to quantum dot nanocrystals, they can be made from elemental semiconductors, like silicon, or they can be made of two elements (binary) or three elements (ternary). By mixing two elements together, several different properties can be achieved, and by combining three, even more properties can be accomplished.
At the flagship institution of the University of Illinois system, the researchers focused on just a single kind of element, which they believe can be the ‘perfect’ material to make. The material here is mercury cadmium selenide. According to Smith:
“You could basically get any property you want by changing the ratio of cadmium and mercury atoms. It can span this huge range of the electromagnetic spectrum—across the entire infrared into the entire visible spectrum—and get so many properties.”
Utilizing the Already Developed QD
Developing high-quality infrared quantum dots has actually been years in the making. For a long time now, the research community has been trying to achieve this, with Smith himself involved since graduate school. But none of the efforts have been successful until now.
Finally, the researchers from the University of Illinois were able to make a new material. They achieved this by taking something that had already been perfected. So, they took what is considered to be the most developed quantum dot and utilized it as what Smith called a ‘sacrificial mold.’
Cadmium selenide (CdSe) is an inorganic compound classified as an II-VI semiconductor of the n-type. It is transparent to infrared (IR) light and highly luminescent but has seen limited use in photoresistors.
As the research noted, CdSe-based colloidal semiconductor nanocrystals have been precisely optimized for photonic applications in the visible spectrum. Modern products actually showcase structural uniformity with nearly a hundred percent quantum yield.
Now, the team took cadmium selenide and replaced the atoms of cadmium (Cd) with the mercury (Hg) ones. Right away, this changed everything into the infrared spectrum while keeping all desired qualities, including strong light emission and strong light absorption.
In order to achieve this, the researchers had to discard the conventional way of synthesizing nanocrystals. The traditional method involves first mixing the precursor elements, and then, under the right conditions, they break down into the desired nanocrystal structure.
However, no conditions have been seen to work for selenide, mercury, and cadmium. So, postdoctoral researcher Lee developed a new method called interdiffusion enhanced cation exchange.
In this process, the team added silver as the fourth element, which brings flaws to the material. This, Smith said, caused “everything to mix together homogeneously. And that solved the whole problem.”
In the end, the team developed mercury selenide (HgSe) and mercury cadmium selenide (HgCdSe) nanocrystals that emit and absorb in the infrared spectrum. Developed from visible spectrum CdSe precursors, which are already well-developed, the new materials kept the desired attributes, including shape, size, and uniformity of the cadmium selenide nanocrystals, while having enhanced absorption.
These homogeneous nanocrystals, HgSe and HgxCd1−xSe alloys, also have tunable bandgaps in the infrared spectrum. As per the research, “after passivation with heteroepitaxial CdZnS shells, photoluminescence wavelengths are tunable in the shortwave infrared by composition without changing size, with 80–91% quantum yield and linewidths near 100 meV.”
Potential Applications of Infrared Quantum Dots
The unique size of small quantum dots, combined with their tunable electronic properties, makes QDs very appealing for new technologies and a variety of applications.
Owing to their ability to emit a rainbow of bright and pure colors, their high extinction coefficient and high efficiencies make quantum dots particularly significant for optical applications, such as LED lights, displays, and photovoltaics. When used in the development of advanced display screens, the technology improves color accuracy and brightness.
Security and surveillance is another sector where they can enhance night vision capabilities and help identify individuals or objects in dark or obscured environments. In the automotive industry, this can help enhance driver assistance systems and improve night driving safety. They can also detect pollutants in the environment and contaminants in water sources.
Due to quantum dots’ small size, which also means they have a sharper state density than higher-dimensional structures, electrons do not have to travel far, which translates to electronic devices that can operate faster. These unique electronic properties are particularly useful for solar cells, transistors, quantum computing, and ultrafast all-optical switches and logic gates.
The small size of QDs also makes them suitable for different biomedical applications like biosensors and medical imaging. Unlike fluorescence-based biosensors, those based on quantum dots can emit a whole spectrum of brighter lights while having little degradation over time. This makes them really beneficial in biomedical applications.
According to the research, the new materials, mercury selenide (HgSe) and mercury cadmium selenide (HgCdSe) nanocrystals, may lead to next-gen imaging techniques.
Infrared quantum dots can revolutionize several industries by allowing the development of next-generation imaging techniques. For instance, in medical imaging, infrared quantum dots can be used to detect tumors and cancer cells early on, help in noninvasive imaging of tissues and organs with clearer and more detailed images, and be used during surgery to improve precision and outcomes.
In the healthcare sector, infrared quantum dots can further be used for cell tracking, visualization, and study of the behavior of molecules within cells. As the research pointed out, the most significant use of infrared quantum dots could be for molecular probes.
Most quantum dots emit in the visible spectrum, allowing for only surface detection. However, infrared light will allow for deeper tissues to be probed. This way, quantum dots that emit in the infrared allow researchers to see almost entirely through, say, a living rodent, which is used as a standard model for most diseases, and identify the locations of specific molecules throughout the body without sacrificing the mice.
All of these usages mean a better understanding of biological processes, the human body, and disease mechanisms, and, in turn, better and more personalized solutions and care.
In addition to all this, infrared imaging with quantum dots can also be used to analyze materials and components, ensure product quality in manufacturing, enhance the resolution of telescopes, and assist in the navigation and operation of spacecraft.
Prominent Companies Working with Imaging Techniques and Infrared Quantum Dots
Now, let’s take a look at the companies at the forefront of advancing imaging techniques and working with quantum dots:
#1. QD Vision
This company is known for its quantum dot technology, particularly in display and imaging applications. Co-founded by Moungi Bawendi a decade ago, the company has been working on commercializing QDs through Color IQ.
Back in 2016, Samsung Electronics acquired QD Vision’s IP for $70 million, which included hundreds of patents. With this strategic move, the idea has been to support the company’s long-term vision of its display, TV, and possibly other businesses. At the time, Samsung said that QD Vision’s IP would become part of the Korea-based company’s R&D efforts to develop advanced implementations of QD TVs. Samsung’s QLED displays promise unparalleled color performance and exceptional image quality, “opening up a new stream of possibilities for the future.”
In Q1 of 2024, Samsung reported an increase of 933% in its operating profit compared to 1Q23. The tech giant is expecting a 15-fold rise in operating profit in 2Q24, driven by semiconductor prices thanks to the AI boom. Despite that, Samsung shares (SMSN) are trading at $1,581, only up 5.54% YTD. The company pays a dividend yield of 1.69%.
#2. Nanoco Group
Listed on the London Stock Exchange under the NANO ticker, Nanoco specializes in the development and manufacture of quantum dots and other nanomaterials. Trading at $0.1949, the shares are down 12.38% YTD, with an EPS (TTM) of 0.06 and a P/E (TTM) of 3.32.
The company recently bought back 330,133 of its ordinary shares, which will be canceled to leave 205,038,038 Ordinary Shares in issue, a move made to enhance shareholder value. During the 2Q24 earnings call, its CEO Brian Tenner talked about Nanoco receiving and fulfilling two commercial production orders. While low volume orders, this means Nanoco is actually transitioning into an actual production company and “expect the demand and volume… to ramp up over time.” The company also signed two joint development agreements with global customers involving two different second-generation nanomaterials for use in infrared sensing.
Nanoco’s core technology involves CFQD® quantum dots, which consist of fluorescent semiconductor nanoparticles and HEATWAVETM quantum dots that are specially designed for use in the sensor industry. While the former has applications in OLED color conversion, μLEDs color conversion, and optical security tagging, the latter technology is for Biometric facial recognition, optical diagnostics, night vision, range finding, and LiDAR applications.
Final Thoughts
As we saw, quantum dots technology promises significant advancement across industries. Researchers are currently further exploring QDs, such as infrared quantum dots, which have unique applications, especially in biological imaging. As the demand for QDs continues to grow and their market size increases, we’ll be seeing even more advancements in the field of quantum dots, which have the capability to revolutionize medical, energy, sensors, and consumer electronics.
