Scientists from Thiruvananthapuram based CSIR-National Institute for Interdisciplinary Science and Technology (CSIR-NIIST) have developed organic filter that allows only near-infrared (NIR) light to pass through it.
The filter was found to absorb light from 300-850 nm (both ultraviolet, visible and part of NIR light) and transmit NIR light from 850-1500 nm.
The researchers developed filter by mixing organogel with transparent polymer (polydimethylsiloxane). The soft organogel was prepared by mixing black dye (diketopyrrolopyrrole or DPP) having an amide group that helps molecules to be in close contact with each other and interact, that causes changes in their optical properties. The amide group helps in binding and self-assembly of molecule leading to formation of soft organogel.
The organogel-based filter has ability to absorb both UV and visible light while allowing NIR light alone to pass through. The nanofibres formed through self-assembly of DPP molecules that are responsible for broad light absorption of material, making it appear dark.
Currently available inorganic filters are expensive and brittle whereas organic filters are easy to process and flexible too. The filter can be used for night vision glasses, night photography. It will also have applications in security and forensics such as identifying blood stains on dark fabric which are invisible to naked eyes but are clearly visible and detectable when viewed through camera with NIR filter.