Ethanol‐Precipitable, Silica‐Passivated Perovskite Nanocrystals Incorporated into Polystyrene Microspheres for Long‐Term Storage and Reusage

Effect of polymethyl methacrylate on in situ patterning of perovskite quantum dots by inkjet printing

The preparation of perovskite quantum dots (PQDs) using an in situ inkjet printing method is beneficial for improving the problems of aggregation and photoluminescence (PL) quenching during long-term storage. However, the stability of PQDs prepared using this method is still not ideal, and the morphology of in situ-printed patterns needs to be optimized. To address these problems, this study introduced polymethyl methacrylate (PMMA) into the process of in situ inkjet printing of PQDs and explored the effect of PMMA on the in situ patterning effect of PQDs. The results showed that using a mixed precursor solution containing a small amount of PMMA as the printing ink can slow down the shrinkage process of ink droplets and improve the uniformity of film formation. As the printing substrate, PMMA provided a suitable high-viscosity environment for the in situ growth of PQDs. This could effectively suppress the coffee ring effect. In addition, the interaction between the C=O=C group in PMMA and metal ion Pb2+ in the CsPbBr3 precursor molecules was favourable to enhancing the density of PQDs. The prepared PMMA-coated CsPbBr3 quantum dots (QDs) pattern had high stability and could maintain at 90.08% PL intensity after 1 week of exposure to air.

Anti-Stokes Photoluminescence in Halide Perovskite Nanocrystals: From Understanding the Mechanism towards Application in Fully Solid-State Optical Cooling

Anti-Stokes photoluminescence (ASPL) is an up-conversion phonon-assisted process of radiative recombination of photoexcited charge carriers when the ASPL photon energy is above the excitation one. This process can be very efficient in nanocrystals (NCs) of metalorganic and inorganic semiconductors with perovskite (Pe) crystal structure. In this review, we present an analysis of the basic mechanisms of ASPL and discuss its efficiency depending on the size distribution and surface passivation of Pe-NCs as well as the optical excitation energy and temperature. When the ASPL process is sufficiently efficient, it can result in an escape of most of the optical excitation together with the phonon energy from the Pe-NCs. It can be used in optical fully solid-state cooling or optical refrigeration.

Gas-Mediated Immunoassay for the Carcinoembryonic Antigen at Atmospheric Pressure with Smartphone Coupling with the Fluorescence Quenching Length of Perovskite Capillary

By combining the photothermal properties of the 3,3',5,5'-tetramethylbenzidine oxidation product (TMBox) with the sensitive quenching of perovskite fluorescence by ammonia gas, a gas-mediated immunoassay at atmospheric pressure was constructed, which took the fluorescence quenching length of perovskite fluorescent capillary as the signal output. First, a CsPbBr₃ perovskite with surface modification of 3-aminopropyl triethoxysilane was synthesized by thermal injection and decorated to the capillary wall by glutaraldehyde cross-linking. In the presence of H₂O₂ and the tumor marker carcinoembryonic antigen (CEA), TMB was oxidized to TMBox by the horseradish peroxidase (HRP)-labeled CEA antibody. The photothermal effect of TMBox at 808 nm laser irradiation increases the concentration of ammonia gas, and the prepared fluorescent capillary can respond sensitively to ammonia gas. The fluorescence quenching length can be observed by the naked eye for a semiquantitative evaluation of CEA concentration. At the same time, we developed a mobile APP for the first time to measure the fluorescence quenching length. In the range of 0-20 ng mL^-1, the quenching length increased linearly with the increase in CEA concentration, and the detection limit was 0.078 ng mL^-1. This method has been successfully used for the detection of CEA in human serum with a recovery of 95.8%-106.5%.

Preparation of Flexible Liquid Crystal Films with Broadband Reflection Based on PD&SLC

A simple and efficient method for the preparation of a film with flexible characteristic and selective reflection of near-infrared light is proposed. Based on the coexistence system (PD&SLC) of polymer dispersed liquid crystals (PDLC) and polymer stabilized liquid crystals (PSLC), it combines the flexibility of PDLC with the selectively reflection of PSLC. Innovative use of step-by-step light curing to achieve microstructural differences in the three-dimensional orientation of the material is proposed. That is, the difference between PDLC and PSLC in the planar orientation, as well as the gradient distribution of cholesteric phase liquid crystal pitch in the cell thickness direction, is observed. While realizing the flexibility of the material, the function of broadening the reflection bandwidth is fulfilled. This method of preparing liquid crystal films is expected to have great potential for applications, such as flexible smart windows, infrared light shielding, and sensors.

Enhanced photoluminescence stability and internal defect evolution of the all-inorganic lead-free CsEuCl3 perovskite nanocrystals

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.

Recent Advances in Ligand Design and Engineering in Lead Halide Perovskite Nanocrystals

Lead halide perovskite (LHP) nanocrystals (NCs) have recently garnered enhanced development efforts from research disciplines owing to their superior optical and optoelectronic properties. These materials, however, are unlike conventional quantum dots, because they possess strong ionic character, labile ligand coverage, and overall stability issues. As a result, the system as a whole is highly dynamic and can be affected by slight changes of particle surface environment. Specifically, the surface ligand shell of LHP NCs has proven to play imperative roles throughout the lifetime of a LHP NC. Recent advances in engineering and understanding the roles of surface ligand shells from initial synthesis, through postsynthetic processing and device integration, finally to application performances of colloidal LHP NCs are covered here.

Colloidal syntheses of zero-dimensional Cs4SnX6 (X = Br, I) nanocrystals with high emission efficiencies

Phase-pure all-inorganic zero-dimensional (0D) tin halide Cs4SnX6 (X = Br, I) nanocrystals (NCs) are successfully prepared for the first time. The as-prepared Cs4SnBr6 NCs exhibit a strongly Stokes-shifted broadband emission with a high photoluminescence quantum yield (PLQY) of 21% at room temperature.

Magneto-Fluorescent Perovskite Nanocomposites for Directed Cell Motion and Imaging

The ability for a magnetic field to penetrate biological tissues without attenuation has led to significant interest in the use of magnetic nanoparticles for biomedical applications. In particular, active research is ongoing in the areas of magnetically guided drug delivery and magnetic hyperthermia treatment. However, the difficulties in tracing these optically nonactive magnetic nanoparticles hinder their usage in medical research or treatment. Here, a new perovskite-based magneto-fluorescent nanocomposite that allows the in situ, real-time optical visualization of magnetically induced cellular movements is reported. A swelling-deswelling technique is employed to capture a cesium lead halide perovskite and magnetite nanoparticles within a biocompatible polyvinylpyrrolidone matrix, to produce a water-dispersible composite that possesses a combination of strong magnetic response and intense fluorescence. The wavelength-tunability of perovskite nanocrystals is taken advantage of to demonstrate simultaneous multicolor fluorescent tagging of cancer stem cells. The magneto-directed motion of the cancer stem cells through a microfluidic channel is also imaged as a proof-of-concept toward an optically traceable magnetic manipulation of biological systems. These dual-functional nanocomposites could find promising applications in advanced biotechnologies, such as in optogenetics, cellular separation, and drug delivery studies.

Stable Perovskite Quantum Dots Coated with Superhydrophobic Organosilica Shells for White Light-Emitting Diodes

Metalammonium lead perovskite (MAPbX₃ , MA=CH₃ NH₃ ⁺ ; X=Cl, Br, I) quantum dots (QDs) have attracted tremendous attention due to their outstanding optical properties. However, they usually suffer from poor stability towards water or moisture, which seriously limits their practical applications. Here, we report a simple and effective approach to improve the stability of MAPbBr₃ QDs by encapsulating them with superhydrophobic fluorinated organosilica (FSiO₂ ) shells. The water-resistant stability of the superhydrophobic MAPbBr₃ QDs/FSiO₂ is significantly enhanced and they display strong fluorescence even after immersion in water for 12 hours. This method is readily extended to prepare superhydrophobic MAPbBr_2.4 Cl_0.6 QDs/FSiO₂ and MAPbI₃ QDs/FSiO₂ powders. These superhydrophobic MAPbX₃ QDs/FSiO₂ can be further used to fabricate white light-emitting diodes (LEDs) with comparable color to pure white emission.

Enhancing the Stability of CH3NH3PbBr3 Nanoparticles Using Double Hydrophobic Shells of SiO2 and Poly(vinylidene fluoride)

The instability of lead halide perovskites (LHPs) has tremendously hindered their practical applications. Although some examples on encapsulating LHPs into a SiO₂ shell have been reported, these SiO₂-coated LHPs still suffer from limited stability. Herein, MAPbBr₃ (MA = CH₃NH₃⁺) nanoparticles encapsulated in double hydrophobic shells of organic functionalized SiO₂ and poly(vinylidene fluoride) (MAPbBr₃@SiO₂/PVDF) are successfully synthesized by infiltrating the MAPbBr₃ precursor solution into hollow siliceous nanospheres and followed by PVDF capping. With the dual protection of SiO₂ and PVDF, the MAPbBr₃@SiO₂/PVDF nanoparticles exhibit drastically improved stability against water and UV-light illumination. A white light-emitting diode with luminous efficiency up to 147.5 lm W^-1 and a color gamut encompassing 120% of National Television System Committee in Commission Internationale de L'Eclairage 1931 color space has been demonstrated using the MAPbBr₃@SiO₂/PVDF nanoparticles as the green light source. This study enlightens new insights into the synthesis of highly stable LHPs-based core-shell-shell architectures toward their practical applications.