Synthesis and Optical Characterization of CdSe/CdS Quantum Dots Toward Quantum Light Emitters
Abstract
The aim of this study is to devise strategies that are to be used to synthesize colloidal quantum dots (QDs) with an optimized photoluminescence (PL) property, especially in terms of enhancement of the controlled growth of the core/shell. In particular, the synthesis of CdSe/CdS was also successfully performed and optical and structural properties of the material were thoroughly characterized, and effective surface passivation was also verified. These characteristics are confirmed by UV-Vis absorption redshift (600 nm to 620 nm) and a large increase in PL intensity, as well as a peak shift between 622 nm and 638 nm. The high crystallinity of the material is an indication of the strong quantum confinement regime with a mean size of the crystal at 5.5 ± 0.5 nm in X-ray diffraction (XRD). Near stoichiometric Cd:(Se+S) ratio of 1:0.92 was determined by energy dispersive X-ray spectroscopy (EDS) analysis. Different longitudinal optical (LO) phonon modes were determined for CdSe (202 cm-1) and CdS (312 cm-1) via Raman spectroscopy. Nevertheless, the upshift of the CdS mode provides direct evidence of compressive stress resulting from a 4% lattice mismatch. These findings demonstrate that incorporating a shell structure onto core CdSe created novel quantum dots with high phase purity. Also, these engineering-enhanced PLQY, from 58.8% in bare CdSe cores to 78% in core/shell QDs. Furthermore, core/shell quantum dots exhibit photostability, maintaining emission intensity for at least 5 months under ambient storage conditions. These properties highlight their enormous potential as robust, tunable emitters for next-generation optoelectronic technologies and fluorescent biomarkers.