New materials change colour under UV light in response to heat and moisture, opening up possibilities for security inks, humidity sensors and white LEDs

 

THEBUSINESSBYTES BUREAU

ROURKELA, OCTOBER 28, 2026

In a development that could pave the way for safer lighting technologies and more reliable anti-counterfeiting measures, researchers at the National Institute of Technology (NIT) Rourkela, in collaboration with scientists from IIT Guwahati, IIT Bombay and the National Institute of Science Education and Research (NISER), Bhubaneswar, have developed lead-free materials that emit different colours of light under ultraviolet (UV) illumination and respond reversibly to changes in temperature and moisture.

The materials, based on bismuth-containing compounds, offer a potential alternative to lead-based photoluminescent materials, which have attracted considerable research interest for their light-emission properties but pose significant environmental and public health concerns owing to the toxicity of lead. The findings could have applications in security systems, sensing technologies and advanced lighting solutions.

Many materials used in light-emitting technologies contain lead, raising concerns about their long-term environmental impact and potential risks to human health. To address this challenge, the researchers investigated bismuth-based compounds, a class of materials that can combine organic and inorganic components to achieve useful optical properties without relying on lead.

The findings have been published in the Journal of Materials Chemistry C in a research paper co-authored by Prof. Saroj L. Samal, Associate Professor in the Department of Chemistry at NIT Rourkela, and his research scholar, Subhasish Sahoo. The other authors are 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 bismuth-based material developed by the team exhibits an unusual response to heat and moisture. When heated, it loses water molecules trapped within its structure, bringing about a structural change that enables it to emit blue light under UV illumination. When exposed to moisture again, the material absorbs water and the blue emission disappears. This reversible process allows its light-emitting behaviour to be controlled by altering the surrounding environmental conditions.

Speaking about the material, Prof. Saroj L. Samal, Associate Professor, said, “The Bi-based organic-inorganic hybrid halide compound is synthesised using cheaper and environmentally friendly constituents through a simple synthesis technique. The most interesting aspect of this material is its ability to undergo reversible structural transformation in response to heat and moisture, accompanied by a change in its light-emission properties.”

The discovery could have significant implications for the protection of important documents and commercial products against counterfeiting. Special inks incorporating the material could be used on certificates, signatures and security labels. Their distinctive optical response could then be examined under UV light following controlled heating, potentially providing an additional means of verifying the authenticity of documents and products.

The material could also find applications in humidity-sensing technologies. Since its light emission changes in response to moisture, it may serve as an optical indicator of humidity levels in food packaging, storage facilities and other environments where moisture needs to be monitored and controlled. Such applications could help identify undesirable changes in storage conditions, subject to further testing and device development.

In a related development, the NIT Rourkela research team has also developed lead-free light-emitting diode (LED) materials capable of producing yellow light under UV illumination. By combining the yellow-emitting material with a commercially available blue-light-emitting material, the researchers produced a white LED with a cool, daylight-like appearance. The resulting white-light system maintained stable emission during continuous operation, indicating its potential for further development in solid-state lighting and light-conversion technologies.

Highlighting the potential applications of the research, Prof. Samal said, “The synthesised compound shows promising potential for reversible luminescence switching, moisture sensing, solid-state lighting and anti-counterfeiting applications.”

The next phase of the research will focus on improving the light-emission efficiency and long-term stability of the materials, while exploring ways to integrate them into practical devices. The researchers also plan to develop more efficient, stimulus-responsive luminescent materials for anti-counterfeiting applications, enhance the sensitivity and reliability of humidity sensors, and optimise the performance of white-light-emitting diodes.

These efforts could help bridge the gap between laboratory research and practical applications, with potential benefits for optical security, environmental monitoring and cost-effective, energy-efficient lighting. By developing materials that respond predictably to external stimuli without relying on lead, the team aims to contribute to the development of safer and more versatile technologies for everyday use.