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

Abstract

InP quantum dots (QDs) have great potential as emitters for solid-state lighting, lasing, and bioimaging without the inherent toxicity concern of Cd and Pb-based emitters. Indium phosphide's small bandgap and high covalency make it uniquely capable of color-pure fluorescence that can be tuned throughout the visible and lower IR spectrum. Until recently, InP-based QDs consistently underperformed when compared with CdSe-based counterparts. Recent efforts to understand indium phosphide's nonclassical growth mechanisms, control the nanocrystal shape, control in situ formation of surface oxides, and grow thick, uniform shells have produced InP-based QDs comparable to their CdSe competitors with >95% quantum yields (QYs) in red, green, and blue emission wavelengths. This review covers the most common synthetic techniques, the most recent theories on InP formation mechanisms, the current understanding of InP surface chemistries, and the breadth of fluorescent properties of InP-based QDs.

Toward Surface Chemistry of Semiconductor Nanocrystals at an Atomic-Molecular Level

“…Although III−V semiconductors (e.g., InP) are typically in a zinc-blende structure, alkanoate ligands can hardly pair with surface indium cations. 54,55 This is so because the surface cations on the zinc-blende (100) and (111) polar facets (also wurtzite (0001) and (1011) polar facets) are with a large yet fractional charge (+1.5 and + 0.75), neither of which could be easily neutralized by carboxylate group(s) at the crowded interface. In addition, for their cations (such as indium ions), the coordination mode in lattice is different from that with carboxylates.…”

“…In addition, for their cations (such as indium ions), the coordination mode in lattice is different from that with carboxylates. 54,55 As a result, growth of III−V semiconductor nanocrystals (e.g., InP ones) was found to be uncompetitive with the nucleation, resulting in a growth bottleneck with common indium alkanoates as the indium precursor and sole ligands. 55,56 To our knowledge, there is no proper facet-ligand pairing for III−V semiconductor nanocrystals reported in the literature, resulting in poorly developed synthetic chemistry.…”

“…Although III–V semiconductors (e.g., InP) are typically in a zinc-blende structure, alkanoate ligands can hardly pair with surface indium cations. , This is so because the surface cations on the zinc-blende (100) and (111) polar facets (also wurtzite (0001) and (10 ) polar facets) are with a large yet fractional charge (+1.5 and + 0.75), neither of which could be easily neutralized by carboxylate group(s) at the crowded interface. In addition, for their cations (such as indium ions), the coordination mode in lattice is different from that with carboxylates. , As a result, growth of III–V semiconductor nanocrystals (e.g., InP ones) was found to be uncompetitive with the nucleation, resulting in a growth bottleneck with common indium alkanoates as the indium precursor and sole ligands. , To our knowledge, there is no proper facet-ligand pairing for III–V semiconductor nanocrystals reported in the literature, resulting in poorly developed synthetic chemistry.…”

Suppressed Auger recombination and enhanced emission of InP/ZnSe/ZnS quantum dots through inner shell manipulation

“…Due to their environment-friendly characteristics and tunable emission wavelength, indium phosphide (InP) QDs have gained intensive attention and are expected to be more promising alternative QDs. [7][8][9][10] Nevertheless, In and P are chemically active elements, and traps induced by oxygen can be easily formed in InP-based QDs, leading to some disadvantages in optical properties such as low PL QY, easy photobleaching, serious PL blinking, etc. 11,12 Studies have shown that growing wide band-gap semiconductor shells ZnS and ZnSe onto the InP core is an efficient method to overcome these drawbacks.…”

“…Due to their environment-friendly characteristics and tunable emission wavelength, indium phosphide (InP) QDs have gained intensive attention and are expected to be more promising alternative QDs. 7–10…”