Incorporation of Zinc in Pre-alloyed CuIn[Zn]S2-ZnS Quantum Dots

Student: Jean Morales

Degree: M.S., July 2021

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 a 100kV JEOL TEM.

Key Results

  • Increasing the amount of zinc while synthesizing the core increases the quantum yield, QY, from 15% to about to 30%.
  • Higher QY core QDs exhibited a smaller increase in QY upon shelling/cation exchange than those with no or little zinc.
  • After 24 hr of cation exchange/shelling the QDs are composed of >98% ZnS.
  • TEM size analysis shows heterogenous size distributions that increase as a function of shelling reaction time.

Conclusions

  • Incorporating zinc in the core synthesis step influences the electronic and optical properties of both alloyed core and post cation exchange.

  • The ratios of Cu and In change as the cation exchange reaction progresses.

  • Cation exchange of the core QDs yields a heterogeneous size distributions.

Future Work

  • Characterization of QDs using XRD and XPS.

  • Investigation of blinking properties.

  • Potential applications on time gated imaging, FLIM, bio tracking.