An atom-thin sheet of molybdenum disulfide can glow when light shines on it. But the light it emits is not simple: it's a mix of two very close colors, which scientists call excitons A and B. They are separated by just a small amount of energy, like two neighboring houses on the same street. Picking out one color without the other is tricky, but it's exactly what's needed: such materials could become the basis for tiny light sources and sensors.

The authors of the study proposed placing hollow gold cylinders next to the sheet, like tiny wells standing upright. Gold can gather light around itself and amplify it, like a lens, but at the nanoscale. By changing the height and width of the cylinder, you can tune it to amplify exactly the color you want — either A or B. A thin insulating spacer is left between the gold and the sheet so that the light isn't quenched but instead gets brighter.

It's like having a guitar with two strings that sound almost the same, and you learn to pluck only one, and louder than before. Such control opens the way to devices where the color of the emission can be switched without changing the material itself.

So future optical chips might look like a semiconductor sheet dotted with gold wells, each responsible for its own shade.