Researchers at UMass Chan Medical School and North Carolina State University have developed a superfluorescence crystal nanoparticle that uses near-infrared light, a wave-length of light beyond what humans can see, to safely produce laser-quality light at room temperature. This discovery, published in Nature Photonics, has the potential to provide an easy-to-operate, nanosized light source for laser-based biomedical applications.
“Our efforts are contributing to the next generation light source technology for biomedical applications,” said Gang Han, PhD, professor of biochemistry & molecular biotechnology. “We believe that this superfluorescence nanoparticle provides a revolutionary solution to bioimaging and phototherapies that await a clean and intensive light source. Superfluorescence emission is an ideal alternative to lasers, as it is sharp and bright.”
Superfluorescence is a special quantum optical phenomenon in which individual light emitters work with each other to assemble into a giant quantum dipole. When properly aligned, it is then capable of producing short intense bursts of light called superfluorescence. Producing it is not easy, though.
“The bulky size and extreme low temperature needed for superfluorescence has made practical applications quite challenging in the biomedical field,” said Dr. Han.
To tackle these limitations, Han and Shuang Fang Lim, PhD, associate professor of physics at North Carolina State University, developed a unique medium to realize superfluorescence at room temperature.
Room temperature superfluorescence is hard to achieve because it is difficult for the atoms to emit together without being ‘kicked’ out of alignment by the surroundings. In Han and Dr. Lim’s nanoparticle however, the light comes from electron orbitals ‘buried’ beneath other electrons, which act as a shield or insulation, allowing superfluorescence even at room temperature.
“In addition, we doped a high concentration of ions in the crystal, making emitters extremely close and much easier to synchronize with each other,” said Han. “The emitter distance in our system is only 0.35 nm, which is 27 times shorter than the emitter distance in the previously reported superfluorescence medium.”
“When we excited the material at different laser intensities, we found that it emits three pulses of superfluorescence at regular intervals for each excitation,” said Dr. Lim, co-corresponding author of the research. “And the pulses don’t degrade—each pulse is two nanoseconds long. So not only does the up-conversion nanoparticle exhibit superfluorescence at room temperatures, it does so in a way that can be controlled.”
Han also noted that based on the smart materials design, the team has demonstrated that the upconverted superfluorescence can occur in both the nanocrystal assembly and in a single nanocrystal, the latter of which was the smallest-ever superfluorescence medium. They were able to produce an extremely sharp superfluorescence emission peak with a full-width at half-maximum as narrow as 2 nanometers in the single nanocrystal level. In addition, the lifetime of upconverted superfluorescence is only 46 nanoseconds, which is 10,000-fold accelerated compared to conventional upconversion luminescence.
“The superfluorescence from a single nanocrystal is very encouraging,” said Han. “Because the size of the medium is less than 500 nanometers, this makes our system an unprecedented alternative to lasers as the light source for biomedical applications. Since superfluorescence from our system does not depend on any cavity or complex medium preparations in the laser, the as-synthesized nanocrystal is ready to be used and it produces a monochromatic, bright, and rapid burst of light at room temperature. In this case, we envision that our product will provide a revolutionary light source at a nanosize and with facile operation for a number of laser-based biomedical applications.”
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