Core/Shell Semiconductor Nanocrystals

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 5; no. 2; pp. 154 - 168
• Main Authors: Reiss, Peter, Protière, Myriam, Li, Liang
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 19.01.2009; WILEY‐VCH Verlag; Wiley-VCH Verlag
• Subjects: Chemical Sciences; core/shell materials; Crystallization; Equipment Design; Light; Material chemistry; Materials Testing; Microscopy, Electron, Transmission; nanocrystals; Nanostructures; Nanotechnology - methods; Oxygen - chemistry; Particle Size; photoluminescence; Quantum Dots; semiconductors; Spectrometry, Fluorescence - methods; Spectrophotometry, Ultraviolet - methods; Surface Properties
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.200800841

Colloidal core/shell nanocrystals contain at least two semiconductor materials in an onionlike structure. The possibility to tune the basic optical properties of the core nanocrystals, for example, their fluorescence wavelength, quantum yield, and lifetime, by growing an epitaxial‐type shell of another semiconductor has fueled significant progress on the chemical synthesis of these systems. In such core/shell nanocrystals, the shell provides a physical barrier between the optically active core and the surrounding medium, thus making the nanocrystals less sensitive to environmental changes, surface chemistry, and photo‐oxidation. The shell further provides an efficient passivation of the surface trap states, giving rise to a strongly enhanced fluorescence quantum yield. This effect is a fundamental prerequisite for the use of nanocrystals in applications such as biological labeling and light‐emitting devices, which rely on their emission properties. Focusing on recent advances, this Review discusses the fundamental properties and synthesis methods of core/shell and core/multiple shell structures of II–VI, IV–VI, and III–V semiconductors. Quantum Dots: This Review gives a survey of the synthesis and properties of colloidal core/shell nanocrystals, combining two or more semiconductors in an onionlike structure (see image). The epitaxial‐type shell enhances the fluorescence quantum yield and photostability in type‐I structures. In cases of different band alignment, the shell(s) strongly influence the emission wavelength and excited‐state lifetime.