Metal gives pigment the blues

Researchers studying manganese oxides unexpectedly discover a new way to achieve blue hue

Some scientists really blew it. They accidentally created a new blue pigment by doping white and black compounds with manganese. The new blue may end up in a variety of paints and inks, perhaps replacing some old standby pigments that can be toxic or unstable.

SCALING TO BLUE Two different oxides gained blue color as manganese was added. Courtesy of Mas Subramanian

Scientists led by Mas Subramanian of Oregon State University in Corvallis were studying manganese oxides because of the compounds’ interesting magnetic and electronic properties. When a tray of samples came out of the furnace where they had been baking at about 1,200 degrees Celsius, the powders emerged a startling blue.

“I’ve never seen a manganese oxide give rise to such beautiful colors,” says Subramanian. “When I saw the compound come out it was so beautifully blue.”

The researchers were working with two compounds, yttrium indium oxide, which is white, and yttrium manganese oxide, which is black. When manganese is added to these compounds it makes a nice short bond with their oxygen atoms. These short bonds and the unusual crystalline structure of the compound yield the blue hue, says Subramanian. When photons of light hit the compound, they excite electrons of manganese and oxygen, which jump to another energy level. The electrons absorb light in the red-green part of the spectrum, but not in the blue, hence the blue is dramatically visible.

Adding manganese to other metal oxides also produced the intense blue color, pinpointing manganese as the source of the blue color.

The research is online and in press in the Journal of the American Chemical Society.

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