Beneficial effects of water in the colloidal synthesis of InP/ZnS core–shell quantum dots for optoelectronic applications

Abstract

We demonstrate that the presence of a small amount of water as an impurity during the hot-injection synthesis can significantly decrease the emission lines full width at half-maximum (FWHM) and improve the quantum yield (QY) of InP/ZnS quantum dots (QDs). By utilizing the water present in the indium precursor and solvent, we obtained InP/ZnS QDs emitting around 530 nm with a FWHM as narrow as 46 nm and a QY up to 45%. Without water, the synthesized QDs have emission around 625 nm with a FWHM of 66 nm and a QY of about 33%. Absorption spectra, XRD and XPS analyses revealed that when water is present, an amorphous phosphate layer is formed over the InP QDs and inhibits the QD growth. This amorphous layer favors the formation of a very thick ZnS shell by decreasing the lattice mismatch between the InP core and the ZnS shell. We further show the possibility to tune the emission wavelengths of InP/ZnS QDs by simply adjusting the amount of water present in the system while keeping all the other reaction parameters (i.e., precursor concentration, reaction temperature and time) constant. As an example of their application in light-emitting diodes (LEDs), the green and red InP/ZnS QDs are combined with a blue LED chip to produce white light.

Near-complete photoluminescence retention and improved stability of InP quantum dots after silica embedding for their application to on-chip-packaged light-emitting diodes

“…As shown in transmission electron microscopic images ( Fig. 2a and b), our InP/ZnSeS/ZnS QDs exhibit a distinctively large size of 7 nm compared to other single- 30,31 and multishelled InP QDs 5,32 with typical diameters <5.5 nm. This implies that the present ZnSeS intermediateshelling strategy in a composition-gradient fashion should lead to the effective relief of substantial interfacial strain between InP core and ZnS outer shell with a large lattice mismatch of 7.7%, thus allowing for a thick shell growth.…”

Interfacial Oxidation and Photoluminescence of InP-Based Core/Shell Quantum Dots

“…We synthesized InP QDs by reacting tris-diethylaminophosphine (DEAP) and indium trichloride in oleylamine in the presence of zinc chloride using the now well-established aminophosphine chemistry. [4][5][6]20,21 InP QDs with a diameter of (3.2 ± 0.4) nm nm are obtained when indium chloride and zinc chloride are used (see Transmission Electron Microscopy TEM image in Figure S1, Supporting Information). 5 As shown in Figure 1a, this concurs with an excitonic feature at 560-570 nm.…”

“…It is therefore possible to make oxide-free InP QDs using the aminophosphine route. 20 Here, we report on the relation between oxidation and the optical properties of InP/ZnS and InP/ZnSe QDs, starting from InP core QDs synthesized using tris-diethylaminophosphine. Importantly, the samples studied shared the same InP core QDs but were oxidized to a different degree during shell growth.…”

Probing Surface Defects of InP Quantum Dots Using Phosphorus Kα and Kβ X-ray Emission Spectroscopy

“…As can be seen from the 16% oxidized component of M-InP, this process was difficult to avoid. A solution 13 C NMR spectrum of the M-InP QDs before purification shows an apparent peak in the expected region for a ketone carbon at 210 ppm ( Figure S8); formation of ketone in the synthesis would be accompanied by the formation of water. There is a notable lack of an acidic proton in the 1 H NMR spectrum of the initial MSCs, suggesting no free carboxylic acid is present prior to synthesis.…”