Rourkela: 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 materials that change their light-emission properties in response to heat and moisture, opening up potential applications in anti-counterfeiting, humidity sensing and lighting technologies.
The research focuses on bismuth-based organic-inorganic hybrid compounds as alternatives to lead-based photoluminescent materials, which raise environmental and health concerns because of lead toxicity.
The findings have been published in the Journal of Materials Chemistry C in a paper co-authored by Prof. Saroj L. Samal and research scholar Subhasish Sahoo of NIT Rourkela, Prof. Parameswar K. Iyer and Chakali Srinivas of IIT Guwahati, Rajanikanta Rana of IIT Bombay, and Prof. Himansu S. Biswal and Laxmipriya Dash of NISER Bhubaneswar.
The team found that the bismuth-based compound undergoes reversible structural changes in response to heat and moisture.
When heated, it releases water trapped within its structure and emits blue light under ultraviolet (UV) exposure. When moisture returns, the material absorbs water again and the blue emission disappears.
“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,” Samal said, adding that the compound could be synthesised using relatively inexpensive, environmentally friendly constituents through a simple technique.
The material could be used in security inks for certificates, signatures and product labels.
Its distinctive response to controlled heating and UV exposure could offer an additional way to verify the authenticity of documents and products.
Its moisture-sensitive light emission could also be explored for humidity sensors in food packaging, storage facilities and other environments where moisture monitoring is important.
In a related development, the team has developed other lead-free materials that emit yellow light under UV exposure.
By combining the yellow-emitting material with a commercially available blue-light-emitting material, the researchers produced a white-light-emitting diode (LED) with a cool, daylight-like appearance.
The lighting system maintained stable light emission during continuous operation, indicating potential for solid-state lighting and light-conversion applications.
Samal said the compounds showed promise for reversible luminescence switching, moisture sensing, solid-state lighting and anti-counterfeiting applications.
The researchers plan to improve light-emission efficiency and long-term stability and explore the materials’ integration into practical devices.
Further testing will be needed to establish their performance and suitability for commercial applications.