Emission Quenching in PbSe Quantum Dot Arrays by Short-Term Air Exposure

Abstract

Clear evidence for two emitting states in PbSe nanocrystals (NCs) has been observed. The flow of population between these two states as temperature increases is interrupted by the presence of nonradiative trap states correlated with the exposure of the NC film to air. Quenching of the higher-energy emission begins after only seconds of exposure, with the effect saturating after several days. Unlike short-term oxygen-related effects in solution, the emission quenching appears to be irreversible, signaling a distinction between surface reactivity in NCs in films and that in solution. The origin of the two emissive centers and the impact of trapping on other NC film properties (e.g., electron/hole mobilities) remain important issues to be resolved.

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

“…Nonmonotonic PL yield persists even after their samples are exposed to a controlled oxygen environment from minutes to hours. This behavior is attributed to PL contributions from two distinct radiative states at different energies in these QD samples, consistent with spectral lineshape analysis, at least in dilute glass-encased samples, No air exposure during QD synthesis or as drop cast; Chappell et al [10]. Same QD drop-cast sample as traces B 2 through B 5 .…”

“…Same QD drop-cast sample as traces B 2 through B 5 . B 2 1 minute of air exposure as drop cast, none during QD synthesis; Chappell et al [10]. B 3 Thirty minutes of air as drop cast, none during QD synthesis; Chappell et al [10].…”

“…The near-infrared photoluminescence (PL) from PbSe and PbSe/CdSe colloidal quantum dots (QDs) with diameters on order 4-6 nm has been studied extensively in solution [1][2][3][4][5] but less so out of solution, where significant applications also exist [6][7][8][9][10][11]. One obstacle that has hindered progress in gaining a quantitative microscopic understanding of the optical emission from this material system has been the lack of consistency of the experimental results reported by different groups.…”

“…One obstacle that has hindered progress in gaining a quantitative microscopic understanding of the optical emission from this material system has been the lack of consistency of the experimental results reported by different groups. Chappell et al [10] and Hughes et al [11] recently reported temperature-dependent emission spectra from ≈5-nm-diameter oleate-capped PbSe QDs with apparent contributions from two distinct radiative transitions, the integrated strength of which varies nonmonotonically from 13 to 325 K. Their synthesis is performed in an airfree environment and, depending on procedural details, the temperature dependence of their samples' emission can be irreversibly sensitive, in drop-cast form, to even minute exposures to air.…”

Temperature-Dependent Optical Properties of Colloidal IV-VI Quantum Dots, Composed of Core/Shell Heterostructures with Alloy Components

“…We take this evidence as proof that the dual band is an intrinsic property of the electronic structure of the samples. 27,30 and exsperimentally 21,23,29,[31][32][33] . These studies have suggested that splitting within the exciton fine structure near the band gap may be responsible 23,27,29 .…”