Unraveling the Origin of Interfacial Oxidation of InP-Based Quantum Dots: Implications for Bioimaging and Optoelectronics

Abstract

Indium phosphide core/shell nanocrystals hold promise to replace heavy-metal-based emissive materials for bioimaging and optoelectronic applications. Uniformity of the shell passivation and the interfacial defects are critical for achieving improved optical properties. A combination of Fourier-transform infrared spectroscopy (FTIR) and liquid and solid-state NMR spectroscopy revealed a strong correlation between interfacial oxidation and photoluminescence of InP-based core/shell quantum dots. Using an automated sequential shell growth approach enabled efficient flow synthesis of InP/ZnSe/ZnS quantum dots, exhibiting high-quantum yields and narrow emission line widths. Feeding individual precursors into the reactor channel in a sequential fashion combined with inline reaction monitoring enabled precise control over layer-by-layer shell passivation of the core particles. Our findings suggest that an unintentional aminolytic reaction between oleylamine and carboxylates (two most commonly used starting materials for colloidal synthesis) introduces oxidative defects during the shelling process, thus limiting their optical properties.

Highly luminescent red-emitting In(Zn)P quantum dots using zinc oxo cluster: synthesis and application to light-emitting diodes

“…Importantly, water and CO 2 produced as ketonization byproducts could induce side reactions such as the surface oxidization of In(Zn)P cores and thus negatively affect optical properties. 37,38 Inspired by this approach, we also used FT-IR spectroscopy to probe the occurrence of ketonization (Fig. 3a).…”

Aminophosphine-derived, high-quality red-emissive InP quantum dots by the use of an unconventional in halide

“…Specifically, bulkier halide ions can render adsorption sites of the growing core sterically less accessible, reducing the surface reaction rate and thus leading to a smaller core size. 13 On that account, large (for red color) and smaller InP cores (for green color) were typically synthesized by choosing InCl 3 13,15–18 and InI 3 , 9,13,14,19 respectively, whilst use of InBr 3 produced an intermediate core size (for yellow color). 13 Meanwhile, synthetic work on InBr 3 -derived InP QDs is very rare probably owing to their inappropriate emission color for display devices.…”

“…30,31 Even in aminophosphine-derived InP QD synthesis, where halides replace carboxylates as metal precursors, such surface oxidation is also likely to form in the course of subsequent shelling, where Zn carboxylates are typically employed as shell precursors. 17,18 The resulting InPO x at the core/shell interface can play a detrimental role as an interfacial defect in PL characteristics. 10,18 For that reason, hydrofluoric acid (HF) treatment at the appropriate stage of shell growth was exquisitely implemented to remove the oxidized surface layer of (TMS) 3 P-derived red InP cores and prevent their re-oxidation during shelling.…”

“…17,18 The resulting InPO x at the core/shell interface can play a detrimental role as an interfacial defect in PL characteristics. 10,18 For that reason, hydrofluoric acid (HF) treatment at the appropriate stage of shell growth was exquisitely implemented to remove the oxidized surface layer of (TMS) 3 P-derived red InP cores and prevent their re-oxidation during shelling. 10 As compared in high-resolution XPS scans of P 2p photoelectron peaks of InBr 3 - versus InCl 3 -based InP cores (Fig.…”

“…32 Unfortunately, however, their PL bandwidth was as broad as 60 nm, which is similar to those obtainable from the previous aminophosphine-based red InP QDs. 15–18…”