Junzi Li

Spectroscopic studies of chiral perovskite nanocrystals

As an emerging type of optically active material, semiconductor nanocrystals (NCs) stabilized by chiral molecules have attracted much attention. Owing to the wide range of potential applications of chiral perovskite NCs, the development of these materials is of great importance, but there has been a lack of relevant studies. Here, we describe an investigation of the properties of chiral perovskite NCs obtained using post-synthetic ligand exchange (achiral ligand/chiral ligand). These are found to exhibit mirror-image circular dichroism spectra. It is the chirality of the ligand (enantiomeric 1,2-diaminocyclohexane, DACH) that is most likely responsible for the induction of chiroptical activity in these NCs. Furthermore, their chiroptical properties and the corresponding mechanisms are found to depend strongly on the amount of capping ligand. When excess DACH is used to cap the surface of the NCs, their chiroptical properties are induced mainly by aggregation of DACH on the surface in a chiral pattern. In ...

Thermally activated delayed fluorescence organic dots for two-photon fluorescence lifetime imaging

Autofluorescence is a major challenge in complex tissue imaging when molecules present in the biological tissue compete with the fluorophore. This issue may be resolved by designing organic molecules with long fluorescence lifetimes. The present work reports the two-photon absorption (TPA) properties of a thermally activated delayed fluorescence (TADF) molecule with carbazole as the electron donor and dicyanobenzene as the electron acceptor (i.e., 4CzIPN). The results indicate that 4CzIPN exhibits a moderate TPA cross-section (∼9u2009×u200910−50u2009cm4 s photon−1), high fluorescence quantum yield, and a long fluorescence lifetime (∼1.47u2009μs). 4CzIPN was compactly encapsulated into an amphiphilic copolymer via nanoprecipitation to achieve water-soluble organic dots. Interestingly, 4CzIPN organic dots have been utilized in applications involving two-photon fluorescence lifetime imaging (FLIM). Our work aptly demonstrates that TADF molecules are promising candidates of nonlinear optical probes for developing next-generation multiphoton FLIM applications.Autofluorescence is a major challenge in complex tissue imaging when molecules present in the biological tissue compete with the fluorophore. This issue may be resolved by designing organic molecules with long fluorescence lifetimes. The present work reports the two-photon absorption (TPA) properties of a thermally activated delayed fluorescence (TADF) molecule with carbazole as the electron donor and dicyanobenzene as the electron acceptor (i.e., 4CzIPN). The results indicate that 4CzIPN exhibits a moderate TPA cross-section (∼9u2009×u200910−50u2009cm4 s photon−1), high fluorescence quantum yield, and a long fluorescence lifetime (∼1.47u2009μs). 4CzIPN was compactly encapsulated into an amphiphilic copolymer via nanoprecipitation to achieve water-soluble organic dots. Interestingly, 4CzIPN organic dots have been utilized in applications involving two-photon fluorescence lifetime imaging (FLIM). Our work aptly demonstrates that TADF molecules are promising candidates of nonlinear optical probes for developing next-genera...

Optically Active CdSe-Dot/CdS-Rod Nanocrystals with Induced Chirality and Circularly Polarized Luminescence

Ligand-induced chirality in semiconductor nanocrystals (NCs) has attracted attention because of the tunable optical properties of the NCs. Induced circular dichroism (CD) has been observed in CdX (X = S, Se, Te) NCs and their hybrids, but circularly polarized luminescence (CPL) in these fluorescent nanomaterials has been seldom reported. Herein, we describe the successful preparation of l- and d-cysteine-capped CdSe-dot/CdS-rods (DRs) with tunable CD and CPL behaviors and a maximum anisotropic factor ( glum) of 4.66 × 10-4. The observed CD and CPL activities are sensitive to the relative absorption ratio of the CdS shell to the CdSe core, suggesting that the anisotropic g-factors in both CD and CPL increase to some extent for a smaller shell-to-core absorption ratio. In addition, the molar ratio of chiral cysteine to the DRs is investigated. Instead of enhancing the chiral interactions between the chiral molecules and DRs, an excess of cysteine molecules in aqueous solution inhibits both the CD and CPL activities. Such chiral and emissive NCs provide an ideal platform for the rational design of semiconductor nanomaterials with chiroptical properties.

Plasmon-induced hot electron transfer in AgNW@TiO 2 @AuNPs nanostructures

Compared to the limited absorption cross-section of conventional photoactive TiO2 nanoparticles (NPs), plasmonic metallic nanoparticles can efficiently convert photons from an extended spectrum range into energetic carriers because of the localized surface plasmon resonance (LSPR). Using these metal oxide semiconductors as shells for plasmonic nanoparticles (PNPs) that absorb visible light could extend their applications. The photophysics of such systems is performed using transient absorption measurements and steady extinction simulations and shows that the plasmonic energy transfer from the AgNWs core to the TiO2 shell results from a hot carrier injection process. Lifetimes obtained from photobleaching decay dynamics suggest that (i) the presence of gold nanoparticles (AuNPs) in AgNWs@TiO2@AuNPs systems can further promote the hot carrier transfer process via plasmonic coupling effects and (ii) the carrier dynamics is greatly affected by the shell thickness of TiO2. This result points out a definite direction to design appropriate nanostructures with tunable charge transfer processes toward photo-induced energy conversion applications.

Linear and nonlinear optical characteristics of all-inorganic perovskite CsPbBr3 quantum dots modified by hydrophobic zeolites

All-inorganic perovskite quantum dots (QDs) have been considered as outstanding candidates for high-performance optoelectronic device applications. However, the chemical and optical stabilities restrict their device applications. In this paper, hydrophobic zeolites were proposed to modify CsPbBr3 QDs to prevent water influence while achieving good dispersion. These hybrid luminescent materials possess high internal quantum efficiency (IQE, ∼81%@3.52 W cm-2) and low dissociation levels that give rise to improved optical stability in terms of temperature and time. More interesting, it is found that this nanocomposite is able to maintain its optical limiting performance under intensive laser illumination. This paper discusses the linear and nonlinear optical characteristics of CsPbBr3 QDs, which would be of great importance for both fundamental physics investigation and practical multiphoton applications.