Rourkela (Odisha): Researchers at the National Institute of Technology (NIT) Rourkela, in collaboration with scientists from IIT Guwahati, IIT Bombay and NISER Bhubaneswar, have developed lead-free light-emitting materials that change colour under ultraviolet (UV) light exposure and respond to heat and moisture. The materials could find applications in anti-counterfeiting systems, humidity sensors and advanced lighting technologies.
The research explores bismuth-based compounds as safer alternatives to lead-based photoluminescent materials. Although lead-based compounds have useful light-emitting properties, their toxicity poses significant risks to human health and the environment.
The findings have been published in the Journal of Materials Chemistry C. The paper was co-authored by Prof. Saroj L. Samal, Associate Professor in the Department of Chemistry at NIT Rourkela, and his research scholar Subhasish Sahoo, along with Prof. Parameswar K. Iyer and Chakali Srinivas from IIT Guwahati, Rajanikanta Rana from IIT Bombay, and Prof. Himansu S. Biswal and Laxmipriya Dash from NISER Bhubaneswar.
The developed bismuth-based organic-inorganic hybrid material exhibits reversible changes in its structure and light-emission properties in response to heat and moisture. When heated, it releases water trapped within its structure and emits blue light under UV exposure. When moisture returns, the material absorbs water again, causing the blue emission to disappear. This reversible response makes it promising for sensing and security applications.
Explaining the discovery, Prof. Samal said the compound was synthesised using inexpensive, environmentally friendly constituents through a simple technique. Its ability to undergo reversible structural transformation in response to heat and moisture, accompanied by changes in light emission, is one of its most interesting features.
The material could help prevent counterfeiting of important documents and products. Special inks containing the compound could be applied to certificates, signatures and security labels. Their characteristic response under UV light after controlled heating could provide an additional method of verifying authenticity.
The material may also be useful in humidity sensors, potentially helping monitor moisture levels in food packaging, storage facilities and other environments where humidity control is essential.
In a related development, the NIT Rourkela team has produced lead-free materials that emit yellow light under UV exposure. By combining this material with a commercially available blue-light-emitting material, the researchers developed a white LED producing cool, daylight-like illumination. The system maintained stable light emission during continuous operation, indicating potential for future lighting and light-conversion technologies.
The findings offer promising directions for developing environmentally safer materials for security, sensing and lighting applications, although further development may be needed before commercial deployment.
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