Perovskites enable a unique kind of invisible ink

Researchers at Shanghai Jiao Tong University in China have inadvertently created a perovskite-based lead compound that was invisible to the human eye but could be made visible on demand, while attempting to synthesize glowing chemical compounds.

The ink works by converting a lead-based metal organic framework to luminescent perovskite nanocrystals. It is printed using an ordinary inkjet printer onto paper. A person looking at the paper would not be able to see what was written until salt is applied - which would cause a chemical reaction making the information printed on the paper to become visible when exposed to UV light. Applying salt again would cause another reaction, rendering the information invisible again.

PThe researchers suggest the ink could be used to protect confidential or private information on printed documents. The MOFs-based ink could also prove useful in anti-counterfeiting measures. Many currencies already use variations of invisible ink to hide text or pictures from the naked eye. The team notes that the ink could also prove useful with electronics, the original goal of the research. It allows for richer colors on a screen.

Unfortunately, there is one major problem with the ink'the lead it contains is toxic. A person reading the letter would likely come in contact with the ink, possibly experiencing lead poisoning. The researchers acknowledge this problem and report that they are working on a possible solution using tin instead of lead. There is also a question of how many times the ink can be used.