Photostability of Colloidal PbSe and PbSe/PbS Core/Shell Nanocrystals in Solution and in the Solid State

Abstract

The photostability of semiconductor PbSe nanocrystals (NCs) under different storage conditions and the photoluminescence of PbSe NC films on Si substrates under vacuum and under different atmospheres were investigated. The NCs show a small blue shift in both the emission and absorption spectra when stored in solution. This blue shift is accelerated when the particles are stored in room light compared to when the particles are stored in the dark, which indicates that photooxidation is an important process. The photooxidation process is accelerated by irradiating NC solutions with a 450 W xenon lamp. The photobleaching and appearance of a precipitate are attributed to ligand desorption followed by agglomeration. Reversible O 2induced luminescence quenching was observed on a PbSe NC film on Si substrates, which could be addressed by two mechanisms: indirect quenching by alteration of PbSe charging and neutralization dynamics or quenching through direct interaction of O 2 with the exciton. To improve the photostability of PbSe NCs, PbSe/PbS core/shell NCs using (TOP)S (TOP ) trioctylphosphine) and TMS 2 S (TMS 2 ) bis(trimethylsilyl)) as sulfur sources were prepared. However, PbSe/PbS core/shell NCs did not show an increased stability in solution upon irradiation with a xenon lamp when compared with PbSe core NCs. Either the PbS shell is not able to confine the charge carriers or there is incomplete shell passivation with the PbSe core, and as a result these core/shell NCs have comparable stability.

Kinetic analysis of the temperature dependence of PbSe colloidal quantum dot photoluminescence: Effects of synthesis process and oxygen exposure

“…In contrast, our previously reported temperature-dependent PL studies [8] using ≈4-nm-diameter PbSe QDs produced in a similar manner [9,12,13], but with less control over the exposure of the samples to air during synthesis, exhibit monotonic, pure Arrhenius-like decay of integrated PL from 5 to 295 K, and detailed lineshape fits of spectra obtained from several batches over the entire temperature range of 5 to 295 K were consistent with only a single radiative transition.…”

“…* young@phas.ubc.ca Previously we independently reported that the PL from these samples degraded at room temperature under exposure to oxygen [13], but that this effect was entirely reversible.…”

Photoluminescence enhancement in thin films of PbSe nanocrystals

“…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. This type of NCs became very attractive over the last few years as ͑near͒ infrared emitters because of the well controlled liquid-synthesis procedures developed recently 15,16 and the very large Bohr radius ͑46 nm͒ allowing for fine tuning and control of their optical properties.…”

Phase transformation of PbSe/CdSe nanocrystals from core-shell to Janus structure studied by photoemission spectroscopy

“…Figure 1 shows a typical example of a gold-terminated surface covered with densely packed HNCs that was observed either with scanning electron microscopy (SEM) or with scanning tunneling microscopy. As PbSe nanocrystals are known to suffer from a reduction in the quantum yield with time due to the oxidation of the nanocrystal surface, 24 the samples were kept, as often as possible, in a vacuum vessel, in particular, during the transfer between the different experimental systems used for their characterization.…”