Quantum dots are popular alternatives to organic dyes as fluorescent labels for biological imaging and sensing due to their small size, tuneable emission, and photostability. These nanomaterials have found applications in nanoscale photonic, photovoltaic, and light-emitting diode (LED) devices due to their size-dependent optical and electronic properties. These materials have found applications in biological systems and optics.Ĭolloidal semiconductor nanocrystals, which are also called quantum dots (QDs), consist of ~1–10 nm diameter semiconductor nanoparticles that have organic ligands bound to their surface. Precise control of the size, shape, and composition of both the core and the shell enable the emission wavelength to be tuned over a wider range of wavelengths than with either individual semiconductor. In addition, the shell provides protection against environmental changes, photo-oxidative degradation, and provides another route for modularity. CSSNCs address this problem because the shell increases quantum yield by passivating the surface trap states. The core and the shell are typically composed of type II–VI, IV–VI, and III–V semiconductors, with configurations such as CdS/ZnS, CdSe/ZnS, CdSe/CdS, and InAs/CdSe (typical notation is: core/shell) Organically passivated quantum dots have low fluorescence quantum yield due to surface related trap states. These nanocrystals are composed of a quantum dot semiconducting core material and a shell of a distinct semiconducting material. They are unique because of their easily modular properties, which are a result of their size. Ĭore–shell semiconducting nanocrystals ( CSSNCs) are a class of materials which have properties intermediate between those of small, individual molecules and those of bulk, crystalline semiconductors. Electron micrograph of NaYF 4:Yb,Tm nanoparticles coated with ZnO (top left) and corresponding chemical maps confirming their chemical composition.
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