Instead of producing a brighter and more stable nanoparticle for optical applications, scientists discovered that their product displayed a more unexpected characteristic: bursts of superfluorescence that happened at room temperature and at regular intervals.
The research could result in a number of biological investigations as well as the creation of quicker microchips, neurosensors, or materials for use in quantum computing applications.
When the atoms of a substance coordinate and simultaneously emit a brief but powerful burst of light, this is known as superfluorescence. Although crucial for quantum optical applications, the characteristic is extremely challenging to attain at room temperature and for long enough durations to be of use.
A quantum optics phenomenon is superfluorescence. It is the collective fluorescent light emission of an energized group of atoms or ions. Initially, there is no macroscopic dipole moment since the atoms (or ions) are incoherently stimulated (for example, by optical pumping).
The study team created the lanthanide-doped upconversion nanoparticle, or UCNP, in an effort to produce a “brighter” optical material. They created hexagonal ceramic crystals with sizes ranging from 50 nanometers (nm) to 500 nm, tested their lasing capabilities, and made a number of significant advances.
When one atom emits light, another is stimulated to emit more of the same light, a phenomenon known as lasing occurs. Instead, they discovered superfluorescence, in which all of the atoms align first and then emit at the same time.
First, room temperature operation makes applications much easier. And at 50 nm, this is the smallest superfluorescent media currently in existence. Since we can control the pulses, we could use these crystals as timers, neurosensors or transistors on microchips, for example. And bigger crystals could give us even better control over the pulses.
Shuang Fang Lin
Superradiance and superfluorescence are similar, but in the latter there is a macroscopic dipole moment from the start, produced by the excitation process. The excitation is produced by a light pulse so that all of the participating atoms are roughly in the same place on the Bloch sphere.
“When we excited the material at different laser intensities, we found that it emits three pulses of superfluorescence at regular intervals for each excitation,” says Shuang Fang Lin, associate professor of physics at North Carolina State University and co-corresponding author of the research. “And the pulses don’t degrade each pulse is 2 nanoseconds long. So not only does the UCNP exhibit superfluorescence at room temperatures, it does so in a way that can be controlled.”
Because it is challenging for atoms to emit simultaneously without being “kicked” out of alignment by their surroundings, room temperature superfluorescence is challenging to produce. However, in a UCNP, light is produced by electron orbitals that are “buried” beneath other electrons. These orbitals serve as a shield and permit superfluorescence even at normal temperature.
Additionally, UCNP’s superfluorescence is technologically exciting because it is anti-Stokes shifted, meaning that the emitted wavelengths of light are shorter and higher energy than the wavelengths that initiate the response.
“Such intense and rapid anti-Stokes shift superfluorescence emissions are perfect for numerous pioneering materials and nanomedicine platforms,” says Gang Han, professor of biochemistry and molecular biotechnology at University of Massachusetts Chan Medical School and co-corresponding author of the research.
“For example, the UCNPs have been widely used in biological applications ranging from background noise-free biosensing, precision nanomedicine and deep-tissue imaging, to cell biology, visual physiology, and optogenetics.”
“However, one challenge to current UCNP applications is their slow emission, which often makes detection complex and suboptimal. But the speed of anti-Stokes shift superfluoresence is a complete game changer: 10,000 times faster than the current method. We believe that this superfluorescence nanoparticle provides a revolutionary solution to bioimaging and phototherapies that await a clean, rapid and intensive light source.”
UCNP’s unique qualities could lead to its use in numerous applications.
“First, room temperature operation makes applications much easier,” Lim says. “And at 50 nm, this is the smallest superfluorescent media currently in existence. Since we can control the pulses, we could use these crystals as timers, neurosensors or transistors on microchips, for example. And bigger crystals could give us even better control over the pulses.”
