Luminescent Anisotropic Wurtzite InP Nanocrystals

Abstract

Indium phosphide (InP) nanocrystals are emerging as an alternative to heavy metal containing nanocrystals for optoelectronic applications but lag behind in terms of synthetic control. Herein, luminescent wurtzite InP nanocrystals with narrow size distribution were synthesized via a cation exchange reaction from hexagonal Cu3P nanocrystals. A comprehensive surface treatment with NOBF4 was performed, which removes excess copper while generating stoichiometric In/P nanocrystals with fluoride surface passivation. The attained InP nanocrystals manifest a highly resolved absorption spectrum with a narrow emission line of 80 meV, and photoluminescence quantum yield of up to 40%. Optical anisotropy measurements on ensemble and single particle bases show the occurrence of polarized transitions directly mirroring the anisotropic wurtzite lattice, as also manifested from modeling of the quantum confined electronic levels. This shows a green synthesis path for achieving wurtzite InP nanocrystals with desired optoelectronic properties including color purity and light polarization with potential for diverse optoelectronic applications.

Synthesis, Surface Chemistry, and Fluorescent Properties of InP Quantum Dots

“…Synthesizing anisotropic morphologies such as nanorods and nanoplatelets traditionally requires an anisotropic crystal lattice. Stone et al recently produced fluorescent wurtzite InP QDs via cation exchange from hexagonal Cu 3 P nanocrystals . These spherical QDs contain <1% Cu after exchange and NOBF 4 treatment and display up to 40% PLQYs without shelling.…”

“…Stone et al recently produced fluorescent wurtzite InP QDs via cation exchange from hexagonal Cu 3 P nanocrystals. 141 These spherical QDs contain <1% Cu after exchange and NOBF 4 treatment and display up to 40% PLQYs without shelling. Expanding our library of InP QDs to anisotropic morphologies is essential to utilizing polarized light transitions for optoelectronic applications.…”

Development of Group III–V Colloidal Quantum Dots for Optoelectronic Applications

“…As a milder etchant, NOBF 4 removes the native insulating ligands, as well as the surface oxide or side products, thereby enhancing the film conductivity 56 or emission properties, as shown in Figure 3a. 57 Ligand manipulation approaches for group III−V CQDs passivation are still in the very early stage, mainly because of the limited atomistic understanding of surface structures. Recently, it has been suggested that Z-type ligands can effectively passivate the deep traps from two-coordinated anions on the group III−V surfaces.…”

“…Moreover, oxides or impurities formed on the surface of CQDs can be etched off. As a milder etchant, NOBF 4 removes the native insulating ligands, as well as the surface oxide or side products, thereby enhancing the film conductivity or emission properties, as shown in Figure a …”

Wurtzite InAs Nanocrystals with Short-Wavelength Infrared Emission Synthesized through the Cation Exchange of Cu3As Nanocrystals

“…Therefore, InAs NCs with anisotropic wurtzite phase can potentially emit photons with desired polarization direction upon proper band structure engineering, which is highly appealing for light extraction applications in optoelectronic display devices. Additionally, the chemical reactivity difference among various facets of wurtzite NCs enables the synthesis of anisotropic heterostructured NCs, such as asymmetric quantum dots, dot-in-rod NCs, and dot-in-plate NCs, which display unique optical properties. − However, colloidal InAs NCs directly produced through molecular precursors unanimously exhibited symmetric zinc-blende crystal structure. − Successful synthesis of metastable wurtzite InAs NCs has never been achieved, presumably due to the relatively large energy difference (∼6.28 meV/atom) between the zinc-blende and wurtzite InAs polytypes …”