Synthetic shape tuning controls blinking suppression for two colors in “seeded” tetrapods

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Quantum dot-seeded tetrapods are a type of nanostructure that is capable of dual light emission – one color is emitted from the quantum dot core and another from four arms protruding from it. For the first time, Los Alamos researchers and colleagues investigated the process of seeded-tetrapod dual emission at the level of single nanostructures. They synthesized a series of tetrapods having different arm lengths and thicknesses to determine the key geometric parameters controlling blinking and photobleaching, and even the attribute of two-color emission itself. This new understanding allowed them to simultaneously control the multicolor emission process and photostability for these engineered nanostructures. Nature Communications published the research.

The researchers’ earlier work in ultrastable non-blinking and non-photobleaching “giant” quantum dots informed these investigations of seeded tetrapods. The investigators discovered that the more complex and asymmetric tetrapods are an even more versatile platform for controlling and fine-tuning emission processes of nanoscale semiconductors. For this study they combined traditional (but optimized) tetrapod synthetic techniques with techniques developed previously only for quantum dots. The team used widefield optical microscopy, single-photon-counting, and ensemble transient absorption techniques to assess the complete tetrapod shape series. This information enabled them to establish a new mechanistic understanding for dual-color multiexcitonic emission. The researchers determined the structural parameters for intentionally “engineering” unprecedented performance metrics of blinking-suppressed two-color multiexcitonic and even tricolor photoluminescence.

Semiconductor nanostructures that can emit from two excited states and therefore produce two photoluminescence colors are of fundamental significance and have potentially useful technological uses. For example, these materials could be used in energy applications such as nanoscale thermometers for highly sensitive ratiometric temperature sensing or new photon sources for white-light generation. Dual-emitting nanostructures are model systems for understanding exciton generation and even more complex multiexciton formation and radiative-relaxation processes in quantum-confined structures.

“Materials by design” is a centerpiece of the Laboratory’s Materials for the Future science pillar. The ability to correlate nanoscale architectures with functionality is a key step toward achieving this goal. Underpinning the approach is the need for sophisticated synthetic strategies that can target the most useful nanocrystals.

Reference: “Using Shape to Turn Off Blinking for Two-Colour Multiexciton Emission in CdSe/CdS Tetrapods,” Nature Communications 8, 15083 (2017); doi: 10.1038/ncomms15083. Authors: Noah J. Orfield, Zhongjian Hu, Sachidananda Krishnamurthy, Han Htoon, and Jennifer A. Hollingsworth (Materials Physics Applications – Center for Integrated Nanotechnologies, MPA-CINT); Nimai Mishra and Feng Wang (formerly MPA-CINT); Joanna L. Casson (Physical Chemistry and Applied Spectroscopy, C-PCS); Milan Sykora (Inorganic Isotope and Actinide Chemistry, C-IIAC); and Anton V. Malko (The University of Texas at Dallas.

The DOE Office of Basic Energy Sciences’ Division of Materials Science and Engineering primarily funded the research at Los Alamos. Investigators performed work at the Center for Integrated Nanotechnologies (CINT), a DOE Office of Science User Facility operated jointly by Los Alamos and Sandia National Laboratories. CINT User Projects sponsored some aspects of the research. The work supports the Laboratory’s Energy Security mission area and the Materials for the Future science pillar (emergent phenomena theme) by enabling the design of new functionality in tailored material that can perform in ways beyond their basic properties. Technical contact: Jennifer A. Hollingsworth

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Figure 6. Transmission electron microscopy images for a nanoengineered tetrapod shape series composed of cadmium selenide in the core and cadmium sulfide in the arms. (a–d) Transmission electron microscopy images of four tetrapods (also shown schematically) differing in arm diameter and arm length, respectively.