Tuning of Photophysical Properties of ZnCdS Quantum Dots by Varying the Concentration of Capping Ligand

Abstract

Quantum dots (QDs) are zero-dimensional luminescent semiconducting nanocrystals having diameter ranges from 1-10 nm which lead to show distinct optical and electronic properties that include narrow band emission spectra, large absorption coefficient and tunable bandgap energies. This thesis reports tuning of photophysical properties of ternary alloyed ZnCdS QDs by varying the concentration of capping ligand mercaptoacetic acid (MAA). The MAA capped ZnCdS QDs are synthesized via a colloidal method that is the most accessible and inexpensive way. Ternary ZnCdS QDs also known as blue emitters having wide bandgap energy, composition tunable bandgap and size-tunable fluorescence emission. Herein, tuning of photophysical properties of ZnCdS QDs is achieved via increasing the concentration of MAA that results in the decrease in the particle size. Fourier-transform infrared (FTIR) analysis confirmed the successful capping of QD surface with MAA. X-rays diffraction (XRD) pattern revealed that ZnCdS QDs have been synthesized in the cubic phase. A blue shift in absorption wavelength was observed in UV-VIS absorption and PL emission spectra with increasing concentration of MAA. Moreover, this blue shift in wavelength was associated with an increase in bandgap energy which confirmed a strong quantum confinement effect. The size tunable ZnCdS QDs find many applications in the optoelectronic field, for example photovoltaic devices, light emitting diodes (LEDs) and sensors. Moreover, ZnCdS QDs are eco-friendly so they are used in wastewater treatment and in nanomedicines for bioimaging and bio-marking.