Size-dependent dark exciton properties in cesium lead halide perovskite quantum dots
JOURNAL OF CHEMICAL PHYSICS
Authors: Rossi, Daniel; Qiao, Tian; Liu, Xiaohan; Khurana, Mohit; Akimov, Alexey V.; Cheon, Jinwoo; Son, Dong Hee
Abstract
The fine structure of the band edge exciton and the dark exciton photoluminescence (PL) are topics of significant interest in the research of semiconducting metal halide perovskite nanocrystals, with several conflicting reports on the level ordering of the bright and dark states and the accessibility of the emitting dark states. Recently, we observed the intense dark exciton PL in strongly confined CsPbBr3 nanocrystals at cryogenic temperatures, in contrast to weakly confined nanocrystals lacking dark exciton PL, which was explained by the confinement enhanced bright-dark exciton splitting. In this work, we investigated the size-dependence of the dark exciton photoluminescence properties in CsPbBr3 and CsPbI3 quantum dots in the strongly confined regime, showing the clear role of confinement in determining the bright-dark energy splitting (Delta E-BD) and the dark exciton lifetime (tau (D)). We observe the increase in both Delta E-BD and tau (D) with increasing quantum confinement in CsPbBr3 and CsPbI3 QDs, consistent with the earlier predictions on the size-dependence of Delta E-BD and tau (D). Our results show that quantum confinement plays a crucial role in determining the accessibility to the dark exciton PL and its characteristics in metal halide perovskite nanocrystals.
Altered thyroid hormone profile in patients with Alzheimer's disease
PSYCHONEUROENDOCRINOLOGY
Authors: Quinlan, Patrick; Horvath, Alexandra; Eckerstrom, Carl; Wallin, Anders; Svensson, Johan
Abstract
Background: Epidemiological studies have linked higher levels of thyroid hormones (THs) to increased risk of Alzheimer's disease (AD), whereas in advanced AD, THs have been unchanged or even decreased. In early AD dementia, little is known whether THs are related to AD neuropathology or brain morphology. Methods: This was a cross-sectional study of 36 euthyroid AD patients and 34 healthy controls recruited at a single memory clinic. Levels of THs were measured in serum and cerebrospinal fluid (CSF). In addition, we determined AD biomarkers (amyloid-beta(1-42), total tau and phosphorylated tau) in CSF and hippocampal and amygdalar volumes using magnetic resonance imaging.2 Results: Serum free thyroxine (FT4) levels were elevated, whereas serum free triiodothyronine (FT3)/FT4 and total T3 (TT3)/total T4 (TT4) ratios were decreased, in AD patients compared to controls. In addition, serum TT4 was marginally higher in AD (p = 0.05 vs. the controls). Other TH levels in serum as well as CSF concentrations of THs were similar in both groups, and there were no correlations between THs and CSF AD biomarkers. However, serum FT3 correlated positively with left amygdalar volume in AD patients and serum TT3 correlated positively with left and right hippocampal volume in controls. Conclusions: Thyroid hormones were moderately altered in mild AD dementia with increased serum FT4, and in addition, the reduced T3/T4 ratios may suggest decreased peripheral conversion of T4 to T3. Furthermore, serum T3 levels were related to brain structures involved in AD development.
COA
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