Detection of Mid-Wavelength Infrared Without Mercury or Lead... A Signal for Eco-Friendly Transition in Thermal Imaging and Gas Sensors [Reading Science]

Breaking Free from Toxic Materials
Lowering the Barrier to Commercialization with Low-Cost Processing

A team of Korean researchers has successfully detected mid-wavelength infrared radiation—essential for thermal imaging cameras and body temperature sensing—without using mercury (Hg) or lead (Pb). This technology addresses both the toxicity and high-cost issues of conventional infrared sensors and is being heralded as a potential game-changer across the entire thermal imaging, medical, and environmental sensor industries.

On April 21, the National Research Foundation of Korea announced that Professor Kwangsub Jung’s research team at Korea University has developed a non-toxic photodetector that covers the entire mid-wavelength infrared range (3–5 µm) using silver telluride (Ag₂Te) colloidal quantum dots. The research results were published in the international journal Nature Communications on April 4.

Post-Growth Synthesis Process and Optical Properties of Silver Telluride Colloidal Quantum Dots. This image shows the synthesis and optical characteristics of silver telluride (Ag₂Te) colloidal quantum dots. By using small short-wavelength infrared quantum dots as seeds and performing post-growth at high temperatures, the particle size grows from approximately 6.4 nm to 10.1 nm, and the detection wavelength expands from short-wave to mid-wave infrared (3~5 μm). Precise control of the detection wavelength is achieved simply by adjusting the reaction time, demonstrating the overcoming of previous size limitations.
Image and description: Professor Kwangsub Jung, Korea University

The mid-wavelength infrared range plays a critical role in industries such as thermal imaging cameras, body temperature sensing, and gas analysis for industrial, medical, and environmental applications. However, most commercially available sensors currently rely on toxic substances like mercury and require expensive vacuum equipment for manufacturing, which limits mass production and expansion into consumer markets.

Quantum Dots Surpass 'Size Limitations'... Achieving Full Mid-Infrared Coverage

To overcome the particle size limitations inherent in conventional colloidal quantum dots, the research team introduced a 'post-growth process.' They used nanoparticles synthesized at 130°C as seeds and further grew the particles at 180°C by adding a silver precursor and a reducing agent.

Through this method, the team succeeded in increasing the quantum dot size from the previous limit (about 6 nm) up to 10.1 nm, and the detection wavelength was extended from the short-wavelength to the mid-wavelength infrared region. Notably, the absorption onset wavelength reached up to 6.9 µm, enabling detection across the entire mid-wavelength infrared band.

The actual device fabricated in this study could clearly distinguish subtle differences in body temperature—specifically between 37°C and 40°C—and demonstrated sharp object imaging in thermal imaging tests. The response speed was measured at 523 nanoseconds (ns), which is the fastest among non-toxic mid-wavelength infrared devices worldwide.

Photo of the research team. From the left: Jinhyuk Lee, Integrated Master's and Ph.D. Program, Soyoung Um, Research Professor, Kwangseop Jeong, Professor. Courtesy of Korea University

"Addressing Toxicity and Cost Simultaneously"... Industrial Scalability in the Spotlight

The core of this research lies not only in its performance but also in its manufacturing process. The team applied a solution process, which coats liquid-phase materials without the need for vacuum equipment, thereby significantly lowering potential production costs.

Professor Kwangsub Jung of Korea University commented, "We have demonstrated that mid-wavelength infrared detection is possible without toxicity by using the eco-friendly material silver telluride. On the basis of this low-cost process, practical applications could be realized in a variety of industries, including medical fever monitoring and air pollution gas detection."

This achievement is significant in that it challenges the ‘dependence on toxic materials’ structure that has plagued mid-wavelength infrared sensors. If future improvements in room-temperature operation and multi-pixel array technologies are realized, the popularization of infrared technology—from thermal imaging cameras to environmental sensors—is expected to accelerate even further.

This content was produced with the assistance of AI translation services.