Incorporation of Zinc Pre-alloying inCuInS2-ZnS Quantum Dots and their Effect on Blinking

Student: Jean Morales

Degree: M.S., December 2020

Major Professor: Dr. Colin Heyes

Research Area(s):

Nanoscience & Engineering

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Background/Relevance

  • Commercially available CdSe quantum dots, QDs, are not suitable for bioimaging applications due to their high toxicity.

  • A solution to this issue is using CuInS2 /ZnS QDs which do not contain heavy metals and have longer fluorescence lifetime but controlling the blinking of these particles remains an issue.

Innovation

  • Incorporating zinc in pre-alloying steps to observe the behavior of the electronic and optical properties of CuInS2  QDs.

  • Establishing a direct correlation between the zinc composition of the QDs and blinking phenomena.

Approach

  • Synthesis of the colloidal core QDs at 230ºC using 〖Cu〗^+, 〖In〗^(3+), 〖 Zn〗^(2+),  and S^(2-)  precursors, a high boiling point organic solvent and a ligand agent.
  • Shelling process takes place at 230ºC and lasts from six to twelve hours.
  • Quantum yield is calculated from absorption and emission data.
  • A fluorescence lifetime analysis is performed.
  • Elemental analysis is done with ICP-MS.
  • Characterization using TEM and XRD.

Key Results

  • Increasing the amount of zinc while synthesizing the core increases the quantum yield, QY, from 15% to close to 30%.
  • After being shelled with an equal amount of zinc, the highest increases in QY were exhibited by the QDs with less zinc in the core, while those with more zinc showed smaller increases.
  • The QDs that exhibited the largest emission blueshift were those with no initial zinc present in the core.

Conclusions

  • Incorporating zinc in a pre-selling step does influence the electronic and optical properties of the QDs.

  • Increasing the zinc concentration pre-shelling increases the quantum yield of the QDs form 15% to up to 30%.

  • Post-shelling, the particles with more initial zinc turned out to display lower QY.

Future Work

  • Characterization of QDs using TEM, XRD and an elemental analysis on both core and core/shell QDs.