An ordinary light bulb is either on or off. But tiny glowing particles, nanocrystals with rare-earth ions, have so far emitted steady light, like small flashlights. Inside such a crystal, there are thousands of emitting ions, and even if one 'gets tired,' the others keep shining. Therefore, blinking, sharp on-and-off switching, was considered impossible for them.
But researchers found a way to make the entire crystal blink as a single unit. They discovered that sometimes a single 'dark spot' randomly appears in the crystal — a quencher molecule that intercepts energy from all neighbors at once. It's as if in an orchestra, one musician suddenly drowns out all the others. The crystal goes dark, then the quencher disappears, and the light returns. This collective blinking lasted for over 15 hours straight, withstood more than 10,000 cycles, and did not damage the crystal.
Blinking can be controlled simply by the laser power: shine a bit stronger, and the crystal blinks more often. This paves the way for ultra-precise microscopy: even in a dense cluster of nanocrystals, each one is individually resolved with a precision of 1.2 nanometers (that's a hundred thousand times thinner than a human hair). Such blinking particles will also be useful for biological labels and for quantum devices where light needs to be reliably switched on and off.
The blinking of nanocrystals is somewhat reminiscent of fireflies: they also flash synchronously, even though each beetle is an independent light source.