According to the authors, the new coating is proposed to be used for paper in order to reduce the amount of paper
Yadong Yin and his team from the University of California, Riverside (USA) studied titanium (TiO2) nanocrystals to create a light-sensitive system.
Nanocrystalline TiO2 is a semiconductor:it darkens when exposed to ultraviolet (UV) light due to charge separation and reduction of the titanium atoms. The darkening can be removed as the oxygen in the air re-oxidizes the titanium and reverses the process.
The research team set itself the goal ofprolong the browning of TiO2 and support color change. They used urea-derived nitrogen as a dopant and added a common, non-toxic substance called diethylene glycol to the crystals. This substance also played a critical role in the color change. The researchers noted that it retains TiO2 in a darkened state.
The team applied the crystals to glass or paper,they formed a uniform coating that could be written on with ultraviolet light. All that was needed to create the inscription was 30 seconds of exposure to UV rays with a wavelength of less than 400 nm. The team emphasized that there is no need to use a strong light source. Lamps in the LED power range were sufficient to produce a high level of contrast on the material.
The authors investigated two methods of light writing.First, they created patterns or printed text by shining a light on a paper or glass substrate through a photomask. They also recorded by hand using a laser pen. Both options produced a high-contrast pattern that remained stable for many hours. It only disappeared when heated, or slowly faded due to oxidation. The team notes that you can extend the life of the print by covering the surface of the film with a protective layer of non-toxic polymer, this will protect the surface from oxygen.
The main advantage of the new system ispossibility of reuse. Research has shown that up to 50 write-erase cycles can be performed without any noticeable loss of contrast. This means that the technology can be used for tasks where reusable surfaces are needed or information needs to be rewritten several times, such as transport tickets, information boards or touch screens.
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