This contributed to the high color-purity excitonic
emission and narrow FWHM of PL spectra of NBE-T-CQDs as demonstrated by the temperature-dependent PL spectra.
These findings represent a crucial step toward the understanding and control of excitonic
effects in van der Waals heterostructures and devices.
The double peak is caused by excitonic
levels and appears, whenever the GaAs buffer is extremely pure .
Recently, Bittner and Silva proposed that energy level fluctuations due to thermal motions can lead to strong quantum mechanical coupling between excitonic
and charge-separated states .
When the size of a nanostructure becomes small enough (typically, smaller than the free charge carrier mean-free path in conductors, or exciton Bohr radius in excitonic
semiconductors), its electronic structure (and thus its dielectric function) can depart from that of the corresponding bulk material and depend on the nanostructure size.
As ZnO nanomaterials have essential excitonic
blue and near-UV emission, which has green luminescence associated with [O.sub.2] vacancies [108,109], and for cellular imaging, there are numerous reports existing in previous studies on the utilization of ZnO nanomaterials.
The exponent n is -1, -1/2,0 (ln), or +1/2 for excitonic
, 1-dimensional, 2-dimensional, or 3-dimensional CPs, respectively.
However, this energy gap becomes higher (1.6-2.44 eV) for nanocrystalline materials because the sizes of the crystallite become comparable to the Bohr excitonic
radius, so this difference could be attributed to quantum confinement effect of PbS nanocrystals .
The luminescence at 450 nm excited in the region near the edge of the intrinsic absorption of the host material, whose intensity is strongly increased at low temperature, can be attributed to excitonic
emission (luminescence of self-trapped excitons or near-defect self-trapped excitons).
ZnO is a self-activated crystal of hexagonal wurtzite structure with direct wide band gap energy of 3.37 eV at room temperature [25, 26], and has a strong excitonic
emission in the ultraviolet range even at room temperature due to its larger excitonic
binding energy of 60 meV which is significantly larger than other materials .
The absorption band is characteristic of the high-level excitonic
excitation absorption of a semiconductor, clearly showing the successful deposition of Pb-Sb-S QDs on the ZnO surface.