Green Synthesis of Size tunable CdSe Nanostructures for Bioapplications

Abstract

Semiconductor quantum dots (QDs) have attracted sustained scientific and technological interest due to their size-dependent electronic structure, tunable optical properties, and strong quantum confinement effects. Among II–VI semiconductors, cadmium selenide (CdSe) quantum dots are particularly significant because of their narrow size distribution–dependent emission, high photoluminescence efficiency, and applicability in optoelectronic devices, bioimaging, photovoltaics, and light-emitting technologies. The present work aims to systematically investigate the structural, morphological, and optical properties of size-tunable and self-organized CdSe quantum dots synthesized using a cost-effective chemical bath deposition (CBD) technique in the presence of suitable surfactants. Emphasis is placed on understanding the correlation between synthesis conditions, nanocrystal size, crystallinity, surface morphology, and optical response.

The structural properties of the synthesized CdSe and CdSe/ZnSe quantum dots were examined using X-ray diffraction (XRD) analysis combined with Rietveld refinement, enabling accurate determination of crystallographic phase, lattice parameters, and crystallite size. Transmission electron microscopy (TEM) was employed to directly visualize particle morphology, size distribution, and core–shell architecture. Surface topography and nanoscale roughness of the deposited thin films were investigated through Raman spectroscopy, atomic force microscopy (AFM), providing both two-dimensional (2D) and three-dimensional (3D) morphological insights. Optical characteristics were evaluated using ultraviolet–visible (UV– Vis) absorption spectroscopy and photoluminescence (PL) spectroscopy under in-situ monitoring conditions to capture size-dependent absorption edge shifts and emission behavior.

The results demonstrate a pronounced quantum confinement effect, evidenced by a systematic blue shift in the absorption edge and band gap energy with decreasing particle size. Comparative analysis of particle size estimated from XRD, high-resolution AFM, and TEM revealed close agreement, confirming the reliability of the synthesis and characterization approach. The average particle sizes were found to be approximately 2.4, and 1.6 nm for CdSe quantum dots, and 2.6, nm for CdSe/ZnSe core–shell nanostructures, respectively. Photoluminescence spectra exhibited sharp band-edge emission with minimal Stokes shift, indicating high crystallinity and low defect density, while broader red-shifted emission components were attributed to surface or trap-state recombination processes.