As technology progresses, it occupies an ever-greater presence in our lives, and as the world population grows, the increasing need for more materials for devices is multiplied by a factor of that population growth. For technology to continue to progress and benefit people worldwide, we need to find and develop sustainable materials to build the devices we are using daily. Photonics – devices employing the technical applications of light in electrical systems – is by no means an outlier in this problem, and sustainable materials for photonics are needed now more than ever.
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Materials for Photonics
Photonics detects, manipulates, transmits, modulates, processes, switches, amplifies, and senses light (photons.) The term has been used to refer to applications of light processing since the first practical semiconductor light-emitting diodes (LEDs) were invented in the early 1960s, and especially since the introduction of optical fibers in the 1970s.
While photonics technically covers the technological manipulation of light in any wavelength, most photonics applications employ light in the visible, infrared, or near-infrared spectra.
Light can be transmitted through any material that is transparent (photons can pass through it.) Glass fiber and plastic fiber are used for optical fibers that guide light along the fiber’s path. Optical fibers can carry far more information than copper wires, and they can do so reliably over hundreds of kilometers without needing any amplification.
Advances in photonics such as optical fibers carry all of the data that makes the modern internet work. Therefore, photonics is a vast manufacturing sector that bears a relatively large proportion of the world’s environmental costs.
Lighting and personal electronics use photonic devices to make useful interventions in our lives, society, and industries – but these two applications represent more than a fifth of all electricity consumption around the world. As well as reducing energy consumption during use, sustainable photonics also need to be made from sustainable materials.
Why are Photonics Materials Unsustainable?
Materials used in photonics today can be unsustainable because the material itself is rare. This means that extensive mining activity needs to take place to yield usable quantities of the material. This extraction process consumes huge amounts of energy, as well as disrupting and in some cases destroying local ecosystems with groundworks, infrastructure, water and energy consumption, as well as water and air pollution.
Photonics materials may also be unsustainable if they require large amounts of energy to manufacture. This is a key challenge for most electronic and information technology today, which makes heavy use of semiconductor materials as binary gate transistors for computer chips. Semiconductor manufacture is a notoriously energy-intensive process that also consumes vast amounts of freshwater.
Rare materials must often be extracted on the other side of the planet to manufacturing facilities. Materials that require excessive energy, water, or human labor to manufacture are often produced in low-income countries where these overheads are cheaper, meaning they also need to be transported to other factories for assembly into final parts and devices.
Finally, photonics materials can be unsustainable due to their end-of-life destination. Materials and device designs that are hard to recycle often end up in landfills, or are processed inefficiently by waste processing systems which are in most cases inadequate at closing production loops for sustainable materials.
Furthermore, photonics materials can often be toxic, resulting in local pollution as well as nanoplastic pollution which has been shown to reach every region of the planet, including both poles and the high peaks of the Swiss Alps.
Recent Advances in Sustainable Photonics Materials
Finding sustainable materials for photonics devices such as optical fibers has been a key focus of research for academia and industry alike for a number of years.
One paper recently summarized the contribution of colloidal quantum dots (QDs) in a future generation of photonics that incorporated sustainable materials. QDs are semiconductor nanocrystals (NCs) that can be processed in solution, significantly reducing the energy costs associated with traditional semiconductor manufacturing.
Since QDs were first described, other NCs have been developed, including nanorods, nanoplatelets, and heterostructures such as core/shell dot-in-dots, dot-in-rods, rod-in-rods, and dot-in-plates. In all cases, NCs can be synthesized in near-ambient conditions, and the manufacturing methods are now mature enough for scaled deployment in the industry.
NCs have numerous photonics applications, such as in LEDs, lasers, bio-imaging techniques, photovoltaic (PV) installation, and as emitters and processors of quantum information in future quantum computing.
NCs can generally perform better than silicon-based semiconductor materials in these applications, increasing the energy efficiency of photonic devices (or energy conversion in the case of PV.) NC fabrication can also take place closer to main assembly locations, reducing the transportation costs associated with new devices.
However, this material class still poses sustainability concerns. NCs require heavy toxic materials such as Cd, Pb and Hg. Scientists are currently working on improving the performance of less toxic alternatives, and on increasing efficiency in processing methods to ensure widespread industry adoption.
References and Further Reading
Grim, J.Q., L. Manna, and I. Moreels (2015). A sustainable future for photonic colloidal nanocrystals. Chemical Society Reviews. Available at: https://doi.org/10.1039/C5CS00285K.
Vaz, R., M.F. Frasco, and M.G.F. Sales (2020). Photonics in nature and bioinspired designs: sustainable approaches for a colourful world. Nanoscale Advances. Available at: https://doi.org/10.1039/D0NA00445F.
Wheeler, M. (2016). Integrated Photonics: A Tale of Two Materials. Photonics.com. [Online] Available at: https://www.photonics.com/Articles/Integrated_Photonics_A_Tale_of_Two_Materials/a60862.