(A) Transmission electron microscope analyses of the ‘giant’ quantum dots reveal a zinc-selenide-rich core and a cadmium sulfide shell. (B) Time resolved emission reveals lifetime tunability by simple alterations to the quantum dots’ structure. The lifetimes can be 10-times greater than similar materials. Image: P. Snee.
(A) Transmission electron microscope analyses of the ‘giant’ quantum dots reveal a zinc-selenide-rich core and a cadmium sulfide shell. (B) Time resolved emission reveals lifetime tunability by simple alterations to the quantum dots’ structure. The lifetimes can be 10-times greater than similar materials. Image: P. Snee.

A new study involving researchers at the University of Illinois at Chicago (UIC) has achieved a milestone in the synthesis of multifunctional photonic nanomaterials.

In a paper in Nano Letters, the researchers report the synthesis of semiconductor ‘giant’ quantum dots, comprising a zinc-selenide-rich core and a cadmium sulfide shell, with record-breaking emissive lifetimes. In addition, these lifetimes can be tuned by making a simple alteration to the material’s internal structure.

The group, which included collaborators from Princeton University and Pennsylvania State University, demonstrated 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.

According to Preston Snee, associate professor of chemistry at UIC and the paper’s senior co-author. this charge carrier separation results in extended radiative lifetimes and 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,” he said.

Snee and the paper’s first author, Marcell Pálmai, a postdoctoral research associate in chemistry at UIC, teamed up with Haw Yang of Princeton and others to excite the quantum dots with light and put them in the ‘exciton’ state. An exciton is an electron/hole charge pair, but in these giant quantum dots, the electron becomes displaced from the center to the shell, where it becomes trapped for upwards of 500 nanoseconds, a record for such nanomaterials.

“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 giant quantum dots also have great potential for fundamental biological discovery. Not only do they emit at red wavelengths, which minimizes scattering, but the long lifetimes allow biological imaging to be performed with less background noise. At the single particle level, they emit continuously, so a research scientist can tag proteins relevant to cancer and follow the biological dynamics without losing track of the signal, which is currently a common problem with such studies.

In future research, the group plans to demonstrate that the giant quantum dots make good components for optical devices such as micron-sized lasers.

This story is adapted from material from the University of Illinois at Chicago, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.