2/20/2023 0 Comments Core shellWeak interaction among the inhomogeneous charged energy states on the surface has been hypothesized to form a band structure. Surface dangling orbitals are localized and carry a slight negative or positive charge. This incomplete bonding (relative to the interior crystal structure) results in atomic orbitals that point away from the surface called "dangling orbitals" or unpassivated orbitals. At the surface of the crystal, the periodicity abruptly stops, resulting in surface atoms having a lower coordination number than the interior atoms. Semiconductor nanocrystals generally adopt the same crystal structure as their extended solids. The quantized energy levels observed in quantum dots lead to electronic structures that are intermediate between single molecules which have a single HOMO- LUMO gap and bulk semiconductors which have continuous energy levels within bands In this size regime, quantum confinement effects lead to a size dependent increasing bandgap with observable, quantized energy levels. Nonradiative recombination can occur through energy release via phonon emission or Auger recombination. The radiative pathway involves electrons relaxing from the conduction band to the valence band by emitting photons with wavelengths corresponding to the semiconductor's bandgap. The luminescent properties of quantum dots arise from exciton decay (recombination of electron hole pairs) which can proceed through a radiative or nonradiative pathway. 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.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |