Date of Graduation

8-2025

Document Type

Thesis

Degree Name

Master of Science in Physics (MS)

Degree Level

Graduate

Department

Physics

Advisor/Mentor

Heyes,Colin

Committee Member

Churchill, Hugh

Second Committee Member

Kohanek, Julia

Third Committee Member

Coridan, Robert

Keywords

Chalcogenide; Nanomaterials; Optical Studies; Quantum dot blinking; Quantum dots; Silver-Indium

Abstract

Developing a non-toxic, high-performance fluorescent nanomaterial is crucial for overcoming the environmental and health restrictions of current cadmium, and lead based quantum dots (QDs), which limit the application of quantum dots in optoelectronics and bioimaging. In this thesis, we synthesized environmentally friendly AgInS2 QDs by a colloidal method, systematically altering the In/Ag precursor ratio from 2 to 6 to study the impact on their optical and photophysical properties. Our goals were to find the optimal stoichiometry for maximum quantum efficiency and stability. We also investigated further improving optical and photophysical properties through shelling with ZnS. The emission spectra appeared broad, but the full width at half maximum (FWHM) decreased from 173 nm to 124 nm when the In/Ag ratio increased from 2 to 6. The quantum yield reached a maximum of 48.57% at In/Ag = 4, beyond what had previously been reported for these QDs. Time-resolved PL revealed that this combination had a remarkably long fluorescence lifetime of 273.08 nm. Next, adding a shell of ZnS increased the QY to 69.6%, while the FWHM reduced to 118 nm. The non-radiative rate constant (knr) ranges from 1.98 × 106 s-1 to 5.03 × 106 s-1 , whereas the radiative rate constant (kr) ranges from 3.85 × 105 s-1 to 1.68 × 106 s-1. Furthermore, single particle fluorescence experiments demonstrated that the shelled QDs were stable, showing blinking significantly less than unshelled QDs. This study shows the importance of using the proper ratio of In/Ag to reduce non-radiative decay and further using a ZnS shell to optimize AgInS2 QDs. Fixing the In/Ag ratio at 4 and adding a shell resulted a high quantum yield of almost 70%, addressing the long-standing problem of low brightness in Cd-free QDs. The finding presents a reproducible technique for creating high efficiency luminescence without using harmful materials. While no device construction or modeling was done, improved stability, reduced blinking, and increased radiative efficiency clearly suggest that these QDs have the potential for future applications in environmentally friendly technologies such as bioimaging or light- emitting devices.

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