Rationally designed synthesis of bright AgInS2/ZnS quantum dots with emission control

Abstract

In the blossoming field of Cd-free semiconductor quantum dots (QDs), ternary I-III-VI QDs have received increasing attention due to the ease of the environmentally friendly synthesis of high-quality materials in water, their high photoluminescence (PL) quantum yields (QYs) in the red and near infrared (NIR) region, and their inherently low toxicity. Moreover, their oxygen-insensitive long PL lifetimes of up to several hundreds of nanoseconds close a gap for applications exploiting the compound-specific parameter PL lifetime. To overcome the lack of reproducible synthetic methodologies and to enable a design-based control of their PL properties, we assessed and modelled the synthesis of high-quality MPA-capped AgInS 2 /ZnS (AIS/ZnS) QDs. Systematically refined parameters included reaction time, temperature, Ag:In ratio, S:In ratio, Zn:In ratio, MPA:In ratio, and pH using a design-of-experiment approach. Guidance for the optimization was provided by mathematical models developed for the application-relevant PL parameters, maximum PL wavelength, QY, and PL lifetime as well as the elemental composition in terms of Ag:In:Zn ratio. With these experimental data-based models, MPA:In and Ag:In ratios and pH values were identified as the most important synthesis parameters for PL control and an insight into the connection of these parameters could be gained. Subsequently, the experimental conditions to synthetize QDs with tunable emission and high QY were predicted. The excellent agreement between the predicted and experimentally found PL features confirmed the reliability of our methodology for the rational design of high quality AIS/ZnS QDs with defined PL features. This approach can be straightforwardly extended to other ternary and quaternary QDs and to doped QDs.

Luminescent Quaternary Ag(InxGa1–x)S2/GaSy Core/Shell Quantum Dots Prepared Using Dithiocarbamate Compounds and Photoluminescence Recovery via Post Treatment

“…Meanwhile, the large Stokes shift observed with the PL from I–III–VI 2 semiconductor QDs reveals the presence of defect levels that cause radiative recombination. This emission mechanism differs from that of II–VI semiconductor QDs, which emit radiation via excitonic recombination. − The defect levels are believed to originate from the lattice imperfections of the core, including the vacancies and interstitial sites of either one or both the cations and anions, which generate donor and acceptor levels in the band gap. , The recombination through these levels typically results in a spectrally broad emission due to the strong coupling between the localized carriers and phonons. ,, Therefore, the research on improving the optical properties of I–III–VI 2 QDs has largely been focused on achieving a stoichiometry of the composition between the group 11, 13, and 16 elements. ,− …”

Synthesis and structure design of I–III–VI quantum dots for white light-emitting diodes

“…43 Furthermore, the microwave-assisted method can rapidly and homogeneously raise the temperature, which reduces the possibility of sharp thermal gradients in reaction conditions, resulting in more uniform nucleation and particle growth. Soares et al 44 synthesized AgInS/ZnS (AIS/ZnS) QDs with a PL QY up to 60% and emission peak adjusted from 630 nm to 700 nm via a microwave-assisted method. By systematically assessing synthetic parameters including reaction time, temperature, Ag : In ratio, MPA : In ratio, pH, and so on, they modelled the correlation between the different synthetic parameters and the optical properties (Fig.…”

“…QD (Ag : In : Zn) refers to the Ag : In : Zn ratio effectively found in the prepared QDs. Reproduced with permission 44.…”

Ternary Quantum Dots in Chemical Analysis. Synthesis and Detection Mechanisms

“…Microwave-assisted synthesis allows to develop methods with high reproducibility to obtain quantum dots with narrow size distribution. This factor is important when QDs are incorporated in analytical sensing techniques [ 38 ].…”

“…Among the different methodologies described, microwave synthesis seems to be the best option to obtain core/shell QDs with higher %QY (60% [ 38 ]), narrow size distribution, and that require less reaction time (minutes) compared to the reflux or solvothermal systems. Unfortunately, there are few methodologies that allow these %QY values, and it is important to develop more strategies to improve this parameter.…”