Researchers develop record breaking 500 times longer lifespans for light-emitting "giant" quantum dots

These light-emitting nanocrystals could help in medical imaging and optics.
Stephen Vicinanza
Quantum Dots
Quantum Dots

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Researchers have discovered a new technique for developing the creation of light-emitting "giant" quantum dots. A photonic nanocrystal substance that can be synthesized and used in medical imaging and optics.

The research was published in the journal Nano Letters.

What is a quantum dot?

Quantum dots are colloidal semiconductor nanocrystals, about the size of an electron. They are synthesized (grown) in a solution, and when a light source is aimed at them, they fluoresce, and stay emitting light for an extended period of time.

The giant quantum dots emit light continuously.

Reaching a new milestone

Researchers at the University of Chicago have reached a new milestone in the development of quantum dots. They have synthesized "giant" quantum dots that will emit light, once fluoresced, for 500 nanoseconds, breaking an old record for such nanomaterials.

The group included researchers from Princeton University, and Pennsylvania State University, as well as those at the lead study laboratory at University of Chicago.

A new property was discovered

The team demonstrated a new property and structure concept that can spatially localize electrons. This new structure allows the electrons to focus on holes within a core or shell heterostructure. This is performed by tuning the charge electron to the kinetic energy of a parabolic potential energy surface.

What the team is reporting

Preston Snee, the associate professor of Chemistry at University of California, and the senior co-author of the paper, said of this charge carrier (electron) separation produces a irradiative properties that last longer over the lifetime of the single-nanoparticle that is also continuous.

“These properties enable new applications for optics, facilitate novel approaches such as time-gated single-particle imaging and create inroads for the development of other new advanced materials,” he said in a statement.

Quantum dots are excited

The researchers were able to place the quantum dot into a state of excitation by placing them in a beam of light, which resulted in an "exciton" state. The exciton state is an electron or hole pair. With the giant quantum dots, the electron becomes offset in the electron shell away from the center or core. The electron becomes trapped in this state and emits light for more than 500 nanoseconds a record for this process.

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The biological imaging of such nanoparticles is the hope of the team. There are further fundamental uses of such radiative semiconductor nanomaterials can be far reaching, even as providers of light in micron lasers.

How this new property helps in biological studies

“As emissive materials, quantum dots hold the promise of creating more energy-efficient displays and can be used as fluorescent probes for biomedical research due to their highly robust optical properties,” the researchers write in the paper. “They are 10 times to 100 times more absorptive than organic dyes and are nearly impervious to photobleaching, which is why they are used in the new Samsung QLED-TV.”

The future for quantum dots

The principle team members have stated that giant quantum dots have a potential to be fundamental in biological discovery. They follow some particular optical processes, like emitting low-scatter red-wavelengths and having less of a background interference from noise.

Research can continue for these larger quantum dots, because of their continuous light emitting properties. Any scientist who is studying cancer can, for instance, tag relevant proteins. Then those proteins can be followed in the course of the cell's lifetime without the loss of biological dynamics. This is a common problem with study fluorescence today.

Abstract

Materials for studying biological interactions and for alternative energy applications are continuously under development. Semiconductor quantum dots are a major part of this landscape due to their tunable optoelectronic properties. Size-dependent quantum confinement effects have been utilized to create materials with tunable bandgaps and Auger recombination rates. Other mechanisms of electronic structural control are under investigation as not all of a material’s characteristics are affected by quantum confinement. Demonstrated here is a new structure–property concept that imparts the ability to spatially localize electrons or holes within a core/shell heterostructure by tuning the charge carrier’s kinetic energy on a parabolic potential energy surface. This charge carrier separation results in extended radiative lifetimes and in continuous emission at the single-nanoparticle level. These properties enable new applications for optics, facilitate novel approaches such as time-gated single-particle imaging, and create inroads for the development of other new advanced materials.