Highly Luminescent Zn(x)Cd(1-x)Se/C Core/Shell Nanocrystals: Large Scale Synthesis, Structural and...

Area of Science:

• Materials Science
• Nanotechnology
• Solid-State Physics

Background:

• Core/shell nanocrystals offer unique properties for various applications.
• Controlled synthesis of Zn(x)Cd(1-x)Se nanocrystals is challenging due to phase and composition variations.

Purpose of the Study:

• To synthesize Zn(x)Cd(1-x)Se/C core/shell nanocrystals on a large scale.
• To investigate the structural, compositional, and optical properties of these nanocrystals.
• To explore the effects of synthesis methods on nanostructure morphology and phase separation.

Main Methods:

• Solid-state precursor synthesis for Zn(x)Cd(1-x)Se/C core/shell nanocrystals.
• Rietveld analysis of X-ray diffraction (XRD) patterns for phase and composition determination.
• Cathodoluminescence (CL) spectroscopy for optical emission analysis at various excitation levels.
• Transmission Electron Microscopy (TEM) for structural characterization.

Main Results:

• Successful large-scale synthesis of Zn(x)Cd(1-x)Se/C core/shell nanocrystals (31-39 nm core, 11-25 nm shell).
• One-step synthesis yielded mixed spherical and tripod nanostructures, while two-step methods produced mainly spherical ones.
• Rietveld analysis indicated dominant cubic phases with higher Zn content.
• TEM revealed composition modulation, suggesting phase separation and spinodal decomposition.
• CL measurements showed distinct, sharp emission peaks from single nanocrystals, varying with composition, phase, and size.
• Thermal quenching of luminescence (60-300 K) indicated activation energies of ~50-70 meV, linked to shallow/deep levels.
• Localized CL spectroscopy confirmed phase separation into Zn- and Cd-rich regions.

Conclusions:

• The synthesis method significantly influences the morphology and phase distribution of Zn(x)Cd(1-x)Se nanocrystals.
• Carbon encapsulation provides effective protection for the nanocrystal core.
• Evidence of simultaneous structural and compositional phase separation highlights the complexity of the synthesis.
• The observed optical properties are directly linked to the intricate structural and compositional variations within the nanocrystals.