Painted image under UV light

A painting on parchment was made with luminescent inks that glow underwater. Credit: C. Chen et al./Angew. Chem. Int. Ed

Chemistry

Coppery inks paint an underwater rainbow

Inexpensive version of luminescent pigment shrugs off water.

Inks that are inexpensive to make and shine brightly under ultraviolet light could be used to manufacture colourful coatings for light-emitting diodes.

To make a brilliantly glowing ink, Hong-Bin Yao at the University of Science and Technology of China in Hefei and his team devised nanoparticles that luminesce when they crystallise, a phenomenon called aggregation-induced emission. Most materials that exhibit such behaviour are based on expensive metals, but the researchers used molecules that contain much cheaper elements — copper and iodine. The team produced inks in a wide palette of colours by adding various organic groups to the main structure.

A QR code printed using the inks was invisible until illuminated with UV light. The inks can even adhere to surfaces underwater.

As a coating on LEDs, the inks can create lights that shine in a rainbow of colours, the authors show.