Rourkela: Researchers from the National Institute of Technology (NIT) Rourkela, in collaboration with scientists from IIT Guwahati, IIT Bombay and NISER Bhubaneswar, have developed bismuth-based, lead-free materials that respond to changes in temperature and moisture, with potential applications in anti-counterfeiting systems, humidity sensors and lighting technologies, officials said on Wednesday.
The materials exhibit changes in their light-emitting properties when exposed to heat and moisture, offering a potential alternative to conventional lead-based photoluminescent materials, which pose environmental and health risks due to lead toxicity.
The findings have been published in the Journal of Materials Chemistry C.
The research team investigated bismuth-based organic-inorganic hybrid compounds as safer alternatives to lead-containing materials used in light-emitting technologies.
According to the researchers, the developed material loses water trapped within its structure when heated and emits blue light under ultraviolet (UV) radiation. When exposed to moisture again, it absorbs water, causing the blue-light emission to disappear.
This reversible change in light emission in response to environmental conditions could make the material useful in applications requiring stimulus-responsive optical properties.
Explaining the findings, Prof. Saroj L. Samal, associate professor in the Department of Chemistry at NIT Rourkela, said the compound was synthesised using relatively inexpensive and environmentally friendly constituents through a simple synthesis technique.
He said the material’s ability to undergo reversible structural transformations in response to heat and moisture, accompanied by changes in its light-emission properties, was one of its most significant features.
The research paper was co-authored by Samal 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 researchers said the material could potentially be used in anti-counterfeiting applications, including security inks for certificates, signatures and product labels. Its optical response under UV light following controlled heating could help establish authentication mechanisms for documents and other items.
The material may also find applications in humidity sensors, as its light-emission properties change with moisture levels. Such sensors could be useful in food packaging, storage facilities and other settings where monitoring humidity is important.
In a related development, the research team has also developed lead-free materials that emit yellow light under UV radiation for potential use in light-emitting diodes (LEDs).
The researchers combined the yellow-light-emitting material with a commercially available blue-light-emitting material to produce white light with a cool, daylight-like appearance. The resulting system maintained stable light emission during continuous operation, indicating its potential for lighting and light-conversion applications.
The team plans to focus on improving the light-emission efficiency and long-term stability of the materials, while exploring their integration into practical devices.
Further research will examine ways to improve sensor sensitivity and reliability, develop materials for anti-counterfeiting applications and optimise the performance of white-light-emitting diodes.
The findings could contribute to the development of materials for optical security, environmental monitoring and energy-efficient lighting, the researchers said.
