![]() In addition, the ZnS shell could absorb high energy photons and then carriers will diffuse into CdSe core, which contributes to the high emission efficiency. Meanwhile, the middle shell (CdS) allows the suppression of strain due to small lattice mismatch between the CdS core and ZnS shell. To solve the problems, a ZnS shell grown on the CdSe/CdS QDs provides efficient confinement of electrons and holes inside the QDs as well as highly photostability. Nevertheless, the large lattice mismatch will create dangling bonds or strain at the interfaces which negatively affect both the PL QY and the photostability 21, 22. In the case of CdSe/ZnS, the ZnS shell would be a more suitable passivation layer for CdSe core owing to its large band gap (3.8 eV for bulk material). However, the small band offset between CdSe and CdS could not provide effective confinement for electrons. As a result, the CdSe/CdS QDs always possess high PL QY than bare QDs 18, 19, 20. In case of CdSe/CdS, the lattice mismatch between the core and shell is relatively small which gives rise to the good crystal quality of the materials. Such weaker interaction will result in the suppression of AR 9.Ī thin shell of a wide band gap semiconductor grown on the emitting QDs could substantially improve their stability 17. In the type-II quantum structures, the hole and electron is confined at different regions, which could decrease the overlapping of the electrons and holes wavefunction. first demonstrates that the AR in CdSe could be efficiently suppressed by coating the QDs with a CdS shell, in which the core-shell structure was known as type-II or quasi-type-II quantum structures 9, 10, 11, 12, 13, 14, 15, 16. ![]() For CdSe QDs, CdS is widely accepted as a better choice for hetero-epitaxy growth. When choosing materials for hetero-epitaxy, many things should be taken into consideration such as lattice constant, energy gap and band offset 7, 8. Various methods have been proposed and demonstrated to solve these problems, and it is widely accepted that heterogeneous material epitaxy is the most effective one. Nevertheless, all these applications have been severely limited not only by the Auger recombination (AR), a nonradioactive process during which an electron-hole pair transfers its energy to a third carrier, but also the photostability and surface defects that could result in non-radiative recombination 6. All these unique properties make them suitable for potential application in the third-generation photovoltaics, light emitting diodes (LEDs) and lasers 1, 3, 4, 5. The experimental result is important for high performance optoelectronic device application based on colloidal QDs.Ĭolloidal semiconductor nanocrystals (NCs), or quantum dots (QDs), exhibit numerous advantages as light emitting materials, owing to their tunable emission, solution processability, and high photoluminescence (PL) quantum yield (QY) 1, 2, 3. The lasing action can maintain under higher temperature up to 312.6 K. Moreover, room temperature lasing based on CdSe/CdS/ZnS QDs coated on a fiber was achieved. It is demonstrated that the CdSe/CdS/ZnS QDs show high photostable and temperature-insensitive emission. The influence of ZnS shell has been investigated by comprehensive spectroscopic characterization. For effective electron confinement, a thin shell of wide band gap ZnS semiconductor was grown on the CdSe/CdS core-shell QDs. However, it will lead to poor photostability due to the small conduction band offset between CdSe core and CdS shell. The core-shell CdSe/CdS QDs can suppress Auger recombination effectively and enhance the emission efficiency. Nanocrystal quantum dots (QDs) have great potential for optoelectronic applications such as light emitting diodes and lasers due to their superior optical properties.
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