Size-confined fixed-composition and composition-dependent engineered band gap alloying induces different internal structures in L-cysteine-capped alloyed quaternary CdZnTeS quantum dots.

Oluwasesan Adegoke,Enoch Y Park

doi:10.1038/srep27288

Abstract

The development of alloyed quantum dot (QD) nanocrystals with attractive optical properties for a wide array of chemical and biological applications is a growing research field. In this work, size-tunable engineered band gap composition-dependent alloying and fixed-composition alloying were employed to fabricate new L-cysteine-capped alloyed quaternary CdZnTeS QDs exhibiting different internal structures. Lattice parameters simulated based on powder X-ray diffraction (PXRD) revealed the internal structure of the composition-dependent alloyed CdxZnyTeS QDs to have a gradient nature, whereas the fixed-composition alloyed QDs exhibited a homogenous internal structure. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) analysis confirmed the size-confined nature and monodispersity of the alloyed nanocrystals. The zeta potential values were within the accepted range of colloidal stability. Circular dichroism (CD) analysis showed that the surface-capped L-cysteine ligand induced electronic and conformational chiroptical changes in the alloyed nanocrystals. The photoluminescence (PL) quantum yield (QY) values of the gradient alloyed QDs were 27–61%, whereas for the homogenous alloyed QDs, the PL QY values were spectacularly high (72–93%). Our work demonstrates that engineered fixed alloying produces homogenous QD nanocrystals with higher PL QY than composition-dependent alloying.

Highlights

The development of alloyed quantum dot (QD) nanocrystals with attractive optical properties for a wide array of chemical and biological applications is a growing research field
Semiconductor quantum dot (QD) nanocrystals are characterized by their band gap properties, which can be tuned by altering their particle size[1,2,3]
powder X-ray diffraction (PXRD) was used to probe the internal structure of the alloyed QDs

Summary

Introduction

The development of alloyed quantum dot (QD) nanocrystals with attractive optical properties for a wide array of chemical and biological applications is a growing research field. Sizetunable engineered band gap composition-dependent alloying and fixed-composition alloying were employed to fabricate new L-cysteine-capped alloyed quaternary CdZnTeS QDs exhibiting different internal structures. The size-tunable optical properties of QDs constitute an attractive feature for different spheres of science and technology, including biolabeling, biosensing, optoelectronics, lasers and bioimaging[4,5,6,7] Another alternative method for tuning QDs semiconductor bandgap is by varying the metal chalcogenide composition via engineered control of the particle stoichiometry[7,8]. The band gap alloying of CdZnTeS QDs was engineered using two fabrication techniques: (i) by employing a fixed composition of the metal chalcogenide to vary the particle size and (ii) by varying the composition of the Cd/Zn chalcogenide molar fraction to obtain QDs with different sizes and compositions. The results revealed that water-soluble L-cysteine-capped alloyed quaternary CdZnTeS QDs have great promise in biological and chemical applications

Objectives

Results

Conclusion