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Reaction network elucidated from high-throughput reaction data acquired by our Nimbus4 robot. (co-advised/User project with Jakob Dahl & Paul Alivisatos, JACS 2020).
Elucidating complex reaction networks that give rise to materials
In this research thrust we map and elucidate the complex reaction networks that govern the synthesis of colloidal nanoparticles and other materials. Our long-term goal is to harness complex reaction schemes to synthesize structures in which the composition and structure of a nanoparticle can be controlled with nanometer-scale precision. Such capabilities are important, e.g., for synthesizing multi-shell heterostructures useful for selectively modulating the photophysical pathways doped nanoparticles and semiconductor quantum dots. Even in homogeneous nanoparticles, increasing the number of components above two elements rapidly expands the experimental space required to simultaneously optimize objectives such as phase purity and size distribution. Our combinatorial nanoscience techniques rapidly accelerate discovery and understanding of the synthetic pathways that produce ternary materials such as CsPbBr3 perovskite nanocrystals (left)
Quantum dot heterostructures for solid state lighting
To control the synthesis of heterostructures, we have developed robotic protocols to synthesize complex heterostructures by repeatedly growing thin layers of material onto seed nanoparticles, as well as one-pot methods that can synthesize complex heterostructures in a single reaction step. Robotic synthesis allows us to, in collaboration with Prof. Jonathan Owen's group at Columbia, systematically map the effect of precursor reactivity, ligands, and temperature. These robotic experiments can reveal a narrow slices of multidimensional parameter space that foster, e.g., the uniform growth of shell material exclusively on the seed particles. This “ideal growth” regime (right) is sandwiched between opposing regimes that lead to homogeneous nucleation of shell material (i.e., secondary nucleation) or to the dissolution of the nanocrystals (i.e., ripening). Kinetic simulations (right) reveal that precursor reaction rate and monomer solubility (ligand concentration) determine the balance between secondary nucleation and ripening. The rapid growth of uniform shells is an essential step in the efficient, high-yield synthesis of multi-shell heterostructures, i.e., for the growth of graded alloy heterostructures that suppress Auger recombination in quantum-dot downconverted solid state lighting, and for controlling energy transfer pathways in UCNPs.
Lanthanide-doped NaYF4 upconverting nanoparticles.
Doped nanocrystals
A major focus of our research is on doped nanoparticles such as lanthanide-doped (UCNPs), whose complex energy transfer networks enable these materials to emit light with higher energy than the incident light. We develop combinatorial methods to synthesize unique combinations of dopants in complex UCNP heterostructures, and we develop techniques to control the assembly of these nanoparticles, e.g., onto non-planar cavities for fabrication of low-threshold microlasers.
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