Effect of oxygen and polymer matrix on photo-induced changes in CdSe quantum dots

Photoinduced Enhancement of Photoluminescence of Colloidal II-VI Nanocrystals in Polymer Matrices

“…From the unchanged position of the EPL band, we can conclude that no noticeable photooxidation (photocorrosion) takes place the under given illumination conditions. This is different from numerous previous results on II-VI NCs in solutions or polymers [ 23 , 32 , 33 , 34 , 35 ], which revealed a blue shift of the optical spectra, indicative of the NC size reduction during exposure to light. Notably, along with restoring the EPL/DPL ratio at longer exposure times, the DPL bands show a blue shift and narrowing, which can be understood as a result of intensity redistribution between the longer- (DPL2) and shorter-wavelength (DPL1) components of the DPL band.…”

“…However, this effect can also arise from a much thicker CdS shell on red-emitting NCs, which were synthesized for a much longer time (100 h) as compared to the green ones (1.5 h). Therefore, the photoenhancement observed in this work is distinct from previous experiments of NCs in polymer matrix, which showed either brightening and spectral changes [24,25,34] or darkening and no spectral changes [34].…”

“…Therefore, the investigation of the temporal behavior of the PL spectra of QDs, in particular in application-relevant environments, such as water solutions or polymer matrices, is vitally important. There are studies of the PL spectra of colloidal II-VI NCs under a prolonged illumination in solutions [ 23 , 24 , 25 , 26 , 27 , 28 ], dried on substrates [ 29 , 30 , 31 ], and embedded in polymers [ 23 , 24 , 32 , 33 , 34 , 35 ]. The studies revealed a puzzling variety of trends in intensity and spectral changes, indicating multifaceted physical and chemical processes underlying the apparent PL photoenhancement, which differ significantly between particular studies.…”

“…The studies revealed a puzzling variety of trends in intensity and spectral changes, indicating multifaceted physical and chemical processes underlying the apparent PL photoenhancement, which differ significantly between particular studies. In most cases, the photoenhancement was studied for NCs possessing only excitonic PL band and was accompanied by a blue-shift of the PL band [ 23 , 34 ], indicative of photocorrosion of the NC (surface).…”

Probing How Various Metal Ions Interact with the Surface of QDs: Implication of the Interaction Event on the Photophysics of QDs

“…As already discussed, ZAIS QDs are less toxic in nature and they also possess different characteristic photophysical properties such as (a) a long tail of absorption in the longer wavelength region, (b) broad emission spectra whose full width at half-maximum (fwhm) is greater than 100 nm, (c) large stoke shifts, and (d) long fluorescence lifetime . However, the broad nature of the emission of ZAIS QDs also indicates the presence of defects within the QDs. , If these defects associated with the QDs are reduced/removed, − then ZAIS QDs are expected to be more interesting in terms of various applications. − We note here that the properties of these QDs can easily be altered by suitable surface ligands which are used for capping the surface of the QDs to stabilize the system. , It is well-known that the surface/interface of colloidal QDs, which are usually formed by organic ligands during the synthetic procedure of chalcogenide QDs, plays an important role in tuning their optical properties. , The surface functionalization of QDs through a chemical process is found to be a very useful approach to bring change in the energies and the spatial distribution of the QDs involving the core as well as surface states . This has been observed due to the fact that surface ligands can control (a) the extent of enrichment of cations and anions on the surface, (b) degree of association of surface ions with the core, (c) the crystal structure and size of QDs when the ligands act as surfactants, and (d) confinement energy of charge carriers .…”