Perovskite materials are prominent candidates for many high-performance optoelectronic devices. The rare-earth lead-free CsEuCl3 perovskite nanocrystals are extremely unstable, which makes it very difficult to study their physicochemical properties and applications. Herein, we improved the stability of rare-earth based CsEuCl3 nanocrystals by employing a silica-coating for the first time. Simultaneously, the naturally formed “hollow” regions with an obviously blue-shifted PL emission were first observed inside the CsEuCl3 nanocrystals during the period of storage. Density functional theory (DFT) calculations showed that the formed “hollow” regions are due to the internal defect evolution in the perovskite lattice, which is also responsible for the increase of the bandgap and the blue-shift of emission. Additionally, the rapid decline of luminescence is probably due to the nanocrystals’ final cracking with the expansion of the “hollow” regions. This work helps to understand the relationship between defects and luminescence properties, and provides guidance for the design of more stable lead-free perovskite nanocrystals.
Methyl-ammonium lead iodide (MAPbI 3 ) perovskite quantum dots (QDs) have emerged as a promising material for photoelectronic, however, they usually suffer intrinsically from the environmental instability and low photoluminescence quantum yield (PLQY), which will seriously impede their commercial applications. Here, we report an internal-external combination strategy by lowering the dose of good solvent and reducing the chain length of amine ligand to simultaneously enhance the air stability and PLQY of MAPbI 3 QDs. The low-dose solvent can effectively reduce internal iodine vacancies defects and external residual solvent molecules, meanwhile, the faster and denser assembly of nimble short-chain (SC) ligand on the MAPbI 3 QDs surface can helpfully enhance the external surface passivation. As a result, compared to MAPbI 3 QDs synthesized by traditional ligand-assisted reprecipitation (LARP) method, the air stability and PLQY of which are improved by more than four orders of magnitude (from a few minutes to dozens of days) and nearly two times (from 42% to 80%) prepared by our strategy. Besides, this strategy can widely tune the color of MAPbX 3 (X = Cl, Br, I) QDs from 388 to 735 nm through regulating components. This internal-external combination strategy can provide some beneficial enlightenment for preparing long-term air-stable hybrid perovskite QDs with high PLQY, which drastically driving their commercial applications.
Xiaoru Dai,Ke Wang,Lei Lei,Shiqing Xu,Yao Cheng,Yuansheng Wang
Lanthanide up-conversion features stepwise multi-photon processes, where the difference in photon number that is required for specific up-conversion process usually leads to significant variance in pumping-related processes/properties. In this work, a pumping-controlled dual-mode anti-counterfeiting strategy is conceived by taking advantage of the combination of up-conversion processes with different photon numbers. The combination of Er 3+ and Tm 3+ , which are spatially separated within a designed core/triple-shell nano-architecture, is taken as an example to illustrate such idea. Upon infrared excitation, the emission color of a designed pattern can be switched from red to purple by increasing the excitation power density from 5 to 11 W/cm 2 , while a bright luminescent trajectory including red, white and blue-green color with different length is observed when rotating the pattern above 600 rpm. In addition, the relative up-conversion emission intensities of the Er 3+ and Tm 3+ ions can be manipulated through tailoring interfacial or inner defects in the core/triple-shell nano-crystals, which enable an ultrahigh sensitivity for the pumping-controlled emission color variation to be observed under excitation power well below 11 W/cm 2 .
危险品化学品经营许可证（带存储）