fluorescence

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.

The solar wind rushes from the Sun to Earth, but the magnetosphere bends the flow and sculpts it into plasma tails. The same motif plays out at the heart of galaxies: jets from accretion disks around black holes are twisted by the invisible hand of a magnetic field.

A sheet of graphene is a mesh of carbon atoms one atom thick. Even the slightest contamination shows up on it, like dust specks on eyeglass lenses. Ten years ago, researchers learned to hide graphene between layers of boron nitride, like placing a fragile sheet between two pieces of plastic wrap.

At night in a dark room, the human body emits a barely perceptible glow. This light is so faint that only highly sensitive detectors can catch it. Some researchers thought this glow from the head could tell us about brain activity — no scanners or wires needed. But when put to the test, the story changed.

A quantum dot is like a tiny lamp that turns on and off at the command of a laser, emitting exactly one photon at a time. But this light has a quirk: the photons don't interact with each other; they fly independently, like random drops from a faucet.

Inside a barium titanate crystal, there's a built-in electric field, like a permanent magnet, but for charges. When a flash of light hits it, electrons are knocked loose and start darting around, colliding with atoms. But the crystal isn't the same in all directions: it has an axis along which the field is strongest.

Twenty-eight seconds: that's how long it took for an automated camera to lock onto a flash in a constellation whose light had traveled for more than nine billion years.

A glowing dot the size of a molecule. Run a current through it, and it flashes like a tiny lightbulb. That's what the experiment with dye molecules on a thin salt film looks like. When current enters a molecule, one electron hands it energy. The molecule immediately gives that energy back, as light. It's like a swing: give it one push, and it rocks and then stills.

When a sunbeam hits a leaf, a relay race begins inside it. The energy of light passes from one chlorophyll molecule to the next until it reaches the reaction center — the place where the chemistry of life kicks off. This relay runs with astonishing accuracy: nearly every quantum of light finds its way.

A cage of sixty carbon atoms, shaped like a soccer ball, lets small molecules slip inside. Carbon buckyballs, fullerenes, pack into a crystal like oranges in a crate, leaving gaps between them. At 570 degrees Celsius and 30 atmospheres of pressure, hydrogen seeped into those gaps.

Light from an ordinary bulb is a stream of individual photons, like drops from a faucet. But there is also light where photons come in pairs, like twins walking together. Such grouped light has long been desired for measuring distances and imaging objects hidden around corners. But sources of this light were either too dim, or their flashes too short for ordinary detectors to catch.

A piece of material glows blue. Heat it up, and the glow turns green, as if someone flipped a switch at a traffic light. That's how the new luminescent thermometer described in the paper works. Inside the material are terbium ions — a rare-earth metal that knows how to shine. At room temperature, they emit blue light.

Some superluminous supernovae show a bright oxygen imprint in their light and expand rapidly, while others do not. It seemed like different phenomena. But supernova PTF12dam broke the rules: as its brightness grew, its oxygen signature changed, shifting from one type to another.

Superfluorescence is a crystal’s synchronized exhale of light. Researchers just witnessed its mirror image: superabsorption, a coordinated inhale. They zapped cheap perovskite nanocrystals with laser pulses (spectroscopy) and saw a time-reversed absorption burst.

Shine a flashlight through a narrow slit, and the beam doesn't stay a thin stripe; it spreads out sideways. Light has a habit of bending around obstacles, and because of that, the smallest spot you can get with an ordinary lens is no smaller than half a wavelength.