Surface Transformation and Photoinduced Recovery in CdSe Nanocrystals

Abstract

CdSe nanocrystals in solution and films can enter a metastable state in which the highly luminescent nanocrystals become dark. This change, which we attribute to a surface transformation, can be caused by heating or by changing the environment of the nanocrystals at room temperature. The metastable transformation is reversed upon illumination of above-band-gap light, at which point the nanocrystals are again highly luminescent.

Defects in quantum dots of IIB–VI semiconductors

“…The inset in this figure shows the aging curves of excitonic (A) and deep-level (B) emissions. Similar darkening effects have been also previously observed [84,85]. The absence of a blue shift in the spectra of photo-aged NCs in Fig.…”

Single-Step Multicolor Fluorescence In Situ Hybridization Using Semiconductor Quantum Dot-DNA Conjugates

“…However, bright fluorescence intensity can be fully recovered on re-exposure to UV light, similar to what has been observed for QDs in nonaqueous solvents (14) and, more recently, inside fixed mammalian cells after QD endocytosis (13). As expected, the photo-brightening time constant (approx 66 s) appears to be an intrinsic property of the QDs, independent of the size of the targeted heterochromatin domains and thus of the number of QDs at the hybridization site.…”

Photoluminescence enhancement in thin films of PbSe nanocrystals

“…1,2 One of the most intriguing phenomena observed with NCs is the enhancement of their photoluminescence ͑PL͒ over time during continuous illumination. [3][4][5][6][7][8][9][10][11][12][13][14] This effect was reported so far mostly for CdSe and CdSe/ ZnS NCs and has induced extensive discussion in literature. Recently it was observed also for PbS NCs embedded in thin polymer films 14 and for PbS NCs in glasses.…”

“…Recently it was observed also for PbS NCs embedded in thin polymer films 14 and for PbS NCs in glasses. 7 Different mechanisms were proposed to explain the PL enhancement but its nature still remains controversial due to the strong dependence of the NCs emissive properties on their surface quality, [3][4][5] as well as on the excitation intensity, 5-8 film morphology, 4,8,9 substrate-NCs interactions, 4,10 and environmental conditions. [11][12][13][14][15] The PL enhancement ͑PLE͒ has not been reported previously for PbSe NCs.…”

“…In fact, our results show the opposite-the PL increase is highest in vacuum. The PL enhancement in vacuum can be understood in terms of two of the proposed mechanisms for PL increase in NCs films-photoinduced surface transformation 3,5,12,14 and photoelectrification. 4,20,21 In the first case, upon illumination of the NCs, optimization of surface-ligand passivation occurs, which neutralizes the existing surface defects.…”