Rourkela, October 28, 2026: Researchers from the National Institute of Technology Rourkela (NIT Rourkela), in collaboration with researchers from IIT Guwahati, IIT Bombay and NISER Bhubaneswar, have developed new materials that can emit different colours of light under ultraviolet (UV) light exposure. These materials respond to changes in heat and moisture and could have applications in security systems, sensors and lighting technologies.
The research investigated bismuth-based compounds as safer alternatives to lead-based photoluminescent materials, which are widely studied for their light-emission properties but raise significant environmental and health concerns because of lead toxicity. Many materials used for producing light contain lead, which is harmful to human health and the environment. To find a safer alternative, the researchers investigated bismuth-based compounds, a class of compounds containing both organic and inorganic components, which can offer useful light-emitting properties without relying on lead.
The findings of this research have been published in the Journal of Materials Chemistry C, in a paper co-authored by Prof. Saroj L. Samal, Associate Professor, Department of Chemistry, and his research scholar, Mr. Subhasish Sahoo, from NIT Rourkela, along with Prof. Parameswar K. Iyer and Mr. Chakali Srinivas from IIT Guwahati, Mr. Rajanikanta Rana from IIT Bombay, and Prof. Himansu S. Biswal and Ms. Laxmipriya Dash from NISER Bhubaneswar. The bismuth-based material developed by the team shows an interesting response to heat and moisture. When heated, it loses water trapped within its structure. This change allows it to emit blue light when exposed to UV light. When moisture returns, the material absorbs water again, and the blue light disappears. This process can be reversed by changing the surrounding conditions.
Speaking about the developed material, Prof. Saroj L. Samal, Associate Professor, said, “The Bi-based organic-inorganic hybrid halide compound is synthesized using cheaper and environmentally friendly constituents utilising 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 change in its light emission properties.”
This discovery has potential for protecting important documents and products from counterfeiting. For example, special inks containing the developed material can be used on certificates, signatures and security labels. Their light-emitting properties could be checked under UV light after controlled heating, which could help verify whether an item is genuine. The developed material could also be useful in humidity sensors. Since its light emission changes with moisture, it may help monitor humidity in food packaging, storage facilities and other places where moisture levels need to be controlled.
In addition, the NIT Rourkela research team has also developed related lead-free LEDs that can produce yellow light when exposed to UV light. The research team combined this yellow-light-emitting material with a commercially available blue-light-emitting material to produce a white LED with a cool, daylight-like appearance. This resulting white-light system maintained stable light emission during continuous operation, suggesting potential for future lighting and light-conversion applications. Speaking about the real-world applications of the developed material, Prof. Samal said, “The synthesized compound shows promising potential for reversible luminescence switching, moisture-sensing, solid state lighting and anti-counterfeiting applications.”
As the next step, the research team plans to explore various methods to improve the light-emission efficiency and long-term stability of these materials and investigate their integration into practical devices. Further studies will focus on developing efficient and stimuli-responsive luminescent materials for anti-counterfeiting, improving the sensitivity and reliability of sensors, and optimising the performance of white-light-emitting diodes. These efforts could help translate the findings into practical technologies for optical security, environmental monitoring and cost-effective, energy-efficient lighting.
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