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 can 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 have 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. Prof. Saroj L Samal, Associate Professor, said, “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 the 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. It 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. 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.