Ultrastable Luminescent Organic-Inorganic Perovskite Quantum Dots via Surface Engineering: Coordination of Methylammonium Bromide and Covalent Silica Encapsulation

Passion fruit-inspired dendritic mesoporous silica nanospheres-enriched quantum dots coupled with magnetism-controllable aptasensor enable sensitive detection of ochratoxin A in food products

Ochratoxin A (OTA) is a powerful mycotoxin present in a variety of food products, and its detection is important for human health. Here, a fluorescent aptasensor is reported for sensitive OTA determination. Specifically, the surface of bio-inspired passion fruit-like dendritic mesoporous silica nanospheres-enriched quantum dots (MSNQs-apt) was first modified with the OTA aptamer as the recognition unit and fluorescence emitter, while the aptamer-complementary DNA (MNPs-cDNA) was linked with the magnetic nanoparticles (MNPs) as the separation element. In the range of 2.56 pg/mL to 8 ng/mL, the proposed aptasensor exhibited satisfactory linearity and a detection limit of 1.402 pg/mL. The developed aptasensor achieved recoveries of 90.98-103.20% and 94.33-107.57 % in red wine and wheat flour samples, respectively. By simply replacing the aptamer, this aptasensor can be easily extended to detection of other analytes, suggesting its potential as a universal detection platform for mycotoxins in food products.

Room-Temperature Synthesis of Air-Stable Near-Infrared Emission in FAPbI3 Nanoparticles Embedded in Silica

Hybrid organic-inorganic and all-inorganic metal halide perovskite nanoparticles (PNPs) have shown their excellent characteristics for optoelectronic applications. We report an atmospheric process to embed formamidinium CH(NH2)2PbI3 (FAPbI3) PNPs in silica protective layer at room temperature (approximately 26 °C) employing (3-aminopropyl) triethoxysilane (APTES). The resulting perovskite nanocomposite (PNCs) achieved a high photoluminescence (PL) quantum yield of 58.0% and good stability under atmospheric moisture conditions. Moreover, the PNCs showed high PL intensity over 1 month of storage (approximately 26 °C) and more than 380 min of PNCs solutions in DI water. The studied near-infrared (NIR) light-emitting diode (LED) combined a NIR-emitting PNCs coating and a blue InGaN-based chip that exhibited a 788 nm electroluminescence spectrum of NIR-LEDs under 2.6 V. This may be a powerful tool to track of muscle and disabled patients in the detection of a blood vessel.

Novel cryogenic dual-emission mechanism of lead-free double perovskite Cs2AgInCl6 and using SiO2 to enhance their photoluminescence and photostability

Lead halide perovskite have attracted world-wide attention regarding their serious hazards on ecological environment and human health. To improve both the emission intensity and stability of Cs₂AgInCl₆, this study explores using SiO₂ to structurally adjust Cs₂AgInCl₆. Note that including SiO₂ changed the growth style and crystal morphology of Cs₂AgInCl₆ from an octahedron to a truncated octahedron. After structural adjustment, the unit cells scattered, and the absorption limit broke. Moreover, SiO₂ was demonstrated to passivate the material's surface to form an anti-oxidation protective layer. Consequently, the photoluminescence emission intensity increased by 181.5% and the stability of Cs₂AgInCl₆ improved by 83.11%. This work provides a methodology and reference for future improvements to the luminescence of Cs₂AgInCl₆. Furthermore, a novel double-emission phenomenon (λ_ex = 365 nm: λ_em ≈ 580 nm; λ_ex = 325 nm: λ_em ≈ 505 nm) of Cs₂AgInCl₆ at cryogenic temperatures (20 K) was discovered; this phenomenon explains the shoulder emission problem of 400-450 nm at room temperature and clarifies the luminescence mechanism of Cs₂AgInCl₆.

CsPbX3/SiOx (X = Cl, Br, I) monoliths prepared via a novel sol-gel route starting from Cs4PbX6 nanocrystals

We developed a facile synthesis of nanocomposite powders of CsPbX₃ nanocrystals (NCs) embedded in silica. The synthesis starts from colloidal Cs₄PbX₆ NCs that are mixed with tetraethyl orthosilicate in the presence of nitric acid, which triggers the sol-gel reaction yielding the formation of SiO_x and the conversion of starting NCs into CsPbX₃ ones. The overall reaction delivers CsPbX₃ NCs encased in a silica matrix. The resulting CsPbX₃/SiO_x nano-composite powders exhibited enhanced moisture and thermal stability in air. Also, when mixing different CsPbX₃/SiO_x samples having diverse anion compositions, no interparticle anion exchange processes were observed, which is a further indication that the silica matrix acts as a robust barrier surrounding the NCs. Finallly, we used these composites as down-converter phosphors on top of a blue light-emitting diode (LED), delivering nearly ideal white light emission with the Commission Internationale de l'Eclairage (CIE) color coordinates (0.32, 0.33).

Ultrastable Carbon Quantum Dots-Doped MAPbBr3 Perovskite with Silica Encapsulation

Having suffered from intrinsic structural lability, perovskite quantum dots (PQDs) are extremely unstable under high-temperature and moisture conditions, which have greatly limited their applications. In this work, we propose a novel method to synthesize ultrastable carbon quantum dots (CQDs)-doped methylamine (MA) lead bromide PQDs with SiO₂ encapsulation (CQDs-MAPbBr₃@SiO₂). The kernel CQDs-MAPbBr₃ is formed by the interaction of carboxyl-rich CQDs with MAPbBr₃ via H-bond, which greatly improves the thermal stability of CQDs-MAPbBr₃. Furthermore, highly compact SiO₂ encapsulates the proposed CQDs-MAPbBr₃ via a facile in situ growth strategy, which effectively enhances the water resistance and air stability of CQDs-MAPbBr₃@SiO₂. As a result, the proposed nanomaterial shows extremely high water stability in aqueous solution for over 9 months and ideal thermal stability with strong fluorescence (FL) emission after 150 °C annealing. Based on the superior stability and ultrahigh FL efficiency of this proposed nanomaterial, a primary sensing method for ion (Ag⁺ and Zn²⁺) FL detection has been developed and the mechanism of PQDs-based ion determination has also been discussed, thus exhibiting the potential applications of CQDs-MAPbBr₃@SiO₂ in the area of FL assay and environment monitoring.

Impact of cesium in methylammonium lead bromide perovskites: insights into the microstructures, stability and photophysical properties

The thermal and moisture instabilities of pure organic lead halide perovskites are the foremost concerns towards the commercialization of perovskite solar cells, which can be avoided by introducing an inorganic cation, such as cesium ion (Cs+) at the A-site of the perovskite crystals. In this report, the impacts of substituted Cs+ cations on the inherent properties such as microstructures, morphology, and photophysics of pure methylammonium lead bromide (MAPbBr3) perovskites have been investigated. Successful formation of mixed MA1-xCsxPbBr3 phases (with 0 ≤ x ≤ 1.0) was predicted from the theoretically calculated tolerance factor, which was further supported by the appearance of sharp diffraction peaks in X-ray diffraction (XRD) patterns without any additional peaks in the whole composition range. Substitution of Cs+ ions brings significant lattice contraction in the parent MAPbBr3 crystal due to the ion size disparity in the ionic radii between MA+ and Cs+ ions. We examine the vibrational signatures of the Raman bands related to the organic MA+ and infer the nature of interactions between the organic moiety and the surrounding inorganic cage as a function of Cs concentration. Raman spectroscopic analysis reveals structural distortion due to the altered H-bonding interaction of the N+-HBr- type between MA+ and the PbBr3- octahedral framework as a function of Cs content, which is responsible for the octahedral tilting in Cs substituted MAPbBr3. We also found hindered rotational motions of MA+ in the octahedral cage of mixed cationic systems, resulting in the orientational ordering of MA in the presence of Cs. These results certainly offer highly ordered mixed phase structures and promote superior thermal stability, as evident from the thermogravimetric analysis. The photoluminescence intensity becomes considerably enhanced at increased substitution levels, which highlights the capability of incorporated Cs+ cations in suppressing non-radiative recombination in a pure MA-based crystal, possibly related to the mitigation of trapping. The substitution of Cs+ with MAPbBr3 allows innovative strategies to improve the proficiency of tandem solar cells by modifying their structural and photophysical properties.

Water-stable and ion exchange-free inorganic perovskite quantum dots encapsulated in solid paraffin and their application in light emitting diodes

Perovskite quantum dots (PQDs) with high quantum efficiency and broad spectral tunability are promising luminescent materials and show potential applications in light-emitting diodes (LEDs). However, PQDs degrade rapidly in atmosphere moisture due to their easy hydrolysis and undergo undesirable spectral changes associated with ion exchanges. Herein, we encapsulated blue, green and red fluorescence-emitting all-inorganic PQDs respectively with hydrophobic solid paraffin to obtain multi-color luminescent paraffin-PQD composites (P-PQDs). The P-PQD composites not only preserve the bright luminescence, but also greatly improve the water resistance of PQDs. Moreover, the anion exchange phenomenon is effectively inhibited for the isolation of PQD nanoparticles by a solid paraffin layer. Finally, blue, green and red luminescent P-PQD microparticles have been synthesized and show promising applications in LEDs.