Herein, we report a new X-type ligand, i.e., organic sulfonium bromide, for high-efficiency CsPbBr 3 and MAPbBr 3 (MA = methylammonium) perovskite nanocrystals (PNCs). We first confirmed the facile synthesis of the titled ligands in N,N-dimethylformamide at room temperature. By reacting dodecylmethylsulfide with allyl bromide, (3-bromopropyl)trimethoxysilane, and 1,4-dibromobutane, respectively, three representative ligands (named DAM, DSM, and DMM) are acquired. All of them result in CsPbBr 3 and MAPbBr 3 PNCs with near-unity photoluminescence quantum yield (PLQY) and decent ambient stability (no less than 90 % PLQY after 2 months) using a room-temperature ligand-assisted reprecipitation technique. Among them, DSM and DMM endow CsPbBr 3 PNCs with higher thermal/light stability arising from the cross-linkable or bidentate ligand structure. Further, DSM-CsPbBr 3 PNCs can be incorporated into polystyrene through in situ thermal polymerization and the composite shows a record-high PLQY of 93.8 %.
Low-dimensional (LD) organic-metal halides (OMHs) have been extensively investigated because of their excellent optical properties. However, the rational synthetic control (dimension regulation) of LD-OMHs has not yet been established well. The effect of organic cations on the luminescence also remains unexplored. Here, we designed a double-chain ammonium salt 1 with two amine functional groups. Using hydrogen bonding between −N−H 3 protons and halogen ions synthesized zero-dimensional (0D) OMH C 12 H 30 N 4 Pb 2 Br 8 (2). Furthermore, through introducing other ionic interactions to regulate the dimension of OMHs, we obtained onedimensional (1D) OMH C 12 H 30 N 4 Pb 2 Cl 7.5 Br 0.5 (3) by anion exchange of 2. Through the in-depth analysis of their crystal structure, it is understood that the design of organic cations and the exchange of anions can regulate the dimension of OMHs through the change of hydrogen bonds in the structure. This sets a foundation for the formation of a synthesis mechanism for LD-OMHs and effective regulation of OMHs dimension. Through crystal structure analysis, experiments, and theoretical calculations, this work proves that the emission of 2 is not dominated by a single factor of organic cations or metal halogen octahedrons but by the interaction of organic cations and metal octahedrons. Moreover, the 1D-OMH 3 shows tunable emissions from blue to white light under varying excitation wavelengths, which provides a foundation for expanding the application of OMHs.
Temperature sensing based on fluorescent semiconductor nanocrystals has recently received immense attention. Enhancing the trap‐facilitated thermal quenching of the fluorescence should be an effective approach to achieve high sensitivity for temperature sensing. Compared with conventional semiconductor nanocrystals, the defect‐tolerant feature of lead halide perovskite nanocrystals (LHP NCs) endows them with high density of defects. Here, hollow mesoporous silica (h‐SiO2) template‐assisted ligand‐free synthesis and halogen manipulation (chloride‐importing) are proposed to fabricate highly defective yet fluorescent CsPbCl1.2Br1.8 NCs confined in h‐SiO2 (CsPbCl1.2Br1.8 NCs@h‐SiO2) for ultrasensitive temperature sensing. The trap barrier heights, exciton–phonon scattering, and trap state filling process in the CsPbCl1.2Br1.8 NCs@h‐SiO2 and CsPbBr3 NCs@h‐SiO2 are studied to illustrate the higher temperature sensitivity of CsPbCl1.2Br1.8 NCs@h‐SiO2 at physiological temperature range. By integrating the thermal‐sensitive CsPbCl1.2Br1.8 NCs@h‐SiO2 and thermal‐insensitive K2SiF6:Mn4+ phosphor into the flexible ethylene–vinyl acetate polymer matrix, ratiometric temperature sensing from 30.0 °C to 45.0 °C is demonstrated with a relative temperature sensitivity up to 13.44% °C−1 at 37.0 °C. The composite film shows high potential as a thermometer for monitoring the body temperature. This work demonstrates the unparalleled temperature sensing performance of LHP NCs and provides new inspiration on switching the defects into advantages in sensing applications.
Aggregation-induced emission (AIE) materials have drawn great attention for applicationsa so rganic light-emitting diodes (OLED) and probes. The applications are, however,r estricted by the complexs yntheses and hydrophobic properties. Herein, ao ne-step synthesis of an AIE materialb ased on imidazole hydrazone is assessed. Protonation of the imidazole-H leads to emission color changef rom yellow to green in the solid state. The emission color is recovered upon imidazole-H + deprotonation. Moreover,t he emission wavelength shifts from 532 to 572 nm by anion exchange. In addition, an enhanced emission (F F up to 22.6 %) was obtained with the Br À anion compared with NTf 2 À ,S bCl 5 À ,P F 6 À ,a nd OTf À anions.X -ray crystallography studies togetherw ith theoretical calculations show that the enhanced emissiono f hydrazone salts arises from strong hydrogen bondingb etween the hydrazone proton andt he halide ion (Cl À or Br À ).
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