Regulating Phase Distribution of Dion-Jacobson Perovskite Colloidal Multiple Quantum Wells Toward Highly Stable Deep-Blue Emission.

Metal halide perovskite colloidal quantum wells (CQWs) hold great promise for modern photonics and optoelectronics. However, current studies focus on Ruddlesden-Popper (R-P) phase perovskite CQWs that contain bilayers of monovalent long-chain alkylamomoniums between the separated perovskite octahedra layers. The bilayers are packed back-to-back via weak van der Waals interaction, resulting in inferior charge carrier transport and easier decomposition of perovskite. This report first creates a new type of perovskite colloidal multiple QWs (CMQWs) in the form of Dion-Jacobson (D-J) structure by introducing an asymmetric diammonium cation. Furthermore, the phase distribution is optimized by the synergistic effect of valeric acid and zwitterionic lecithin, finally achieving pure deep-blue emission at 435 nm with narrow full width at half maximum. The diammonium layer in D-J perovskite CMQWs features extremely short width of only ≈0.6 nm, thereby contributing to more effective charge carrier transport and higher stability. Through the continuous photoluminescence (PL) measurement and corresponding theoretical calculation, the higher stability of D-J perovskite CMQWs than that of R-P structural CMQWs is confirmed. This work reveals the inherent superior stability of D-J structural CMQWs, which opens a new direction for fabricating stable perovskite optoelectronics.

Mapping the Identity of Transition Metal Doping and Surface Passivation in Indium Phosphide with Theoretical Calculation.

Understanding the electronic structure of doped InP quantum dots (QDs) is essential to optimize the material for specific optoelectronic applications. However, current synthesis approaches are often tedious and unfavorable for rational tunning. Herein, a combination of experimental and computational studies was conducted to address the doping mechanism and surface passivation of InP QDs. The successful dopant introduction requires low Cu doping concentration and heavy Mn doping, while the Ag doping amount is relatively moderate. This may correspond to the theoretical doping formation energy presented as Cu (-2.52 eV) < Ag (-1.76 eV) < Mn (-0.38 eV). As for surface passivation, inorganic ions and shell-like ZnS are unraveled through simulational investigation. Chloride ion promotes oriented growth toward tetrahedron morphology while nitrate-passivated InP QDs exhibit blurry transmission electron microscope (TEM) morphology. Correspondingly, the binding energy of chloride ion with (111) facet is -2.13 eV significantly lower than those of (110) and (100) facets. Further, the additional Zn 3d bands are more involved in the formation of conduction band, which optimized the Mn-doped InP with a 0.32 eV bandgap. These experimental and model results provide more microscopic details of doped InP, which can motivate theoretically exact control of guest ion stoichiometry with optimized characteristics for electrical devices.

Facile synthesis of red-emissive carbon dots with theoretical understanding for cellular imaging.

Recently, red emissive carbon dots (R-CDs) have drawn widespread attention on account of their desirable fluorescence properties and good biocompatibility. Despite great efforts, facile synthesis of R-CDs for cellular imaging remains challenging and the fluorescence mechanism of R-CDs is still elusive. Herein, p-phenylenediamine-derived R-CDs with excitation-independency were successfully obtained through a facile solvothermal approach together with proportional precipitation. The fluorescent solvatochromism of R-CDs is realized, while high polarity leads to higher degree of dipole interaction between R-CDs and different solvents, favoring for emissive red-shift. Furthermore, density functional theory is adopted to explore the optical and electronic characteristics of some polycyclic aromatic molecules. Among different configurations, pyridine nitrogen and carbonyl bonds could relatively increase the charge density and significantly narrow the band gap, which can provide a crucial theoretical basis for the precise preparation of R-CDs. Moreover, R-CDs possess favorable cellular imaging ability, which indicates their potential for a promising candidate as fluorescence probes in bioimaging.

Synergistic Effect of Halogen Ions and Shelling Temperature on Anion Exchange Induced Interfacial Restructuring for Highly Efficient Blue Emissive InP/ZnS Quantum Dots.

InP quantum dots (QDs) have attracted much attention owing to their nontoxic properties and shown great potential in optoelectronic applications. Due to the surface defects and lattice mismatch, the interfacial structure of InP/ZnS QDs plays a significant role in their performance. Herein, the formation of In-S and Sx -In-P1-x interlayers through anion exchange at the shell-growth stage is revealed. More importantly, it is proposed that the composition of interface is dependent on the synergistic effect of halogen ions and shelling temperature. High shelling temperature contributes to the optical performance improvement resulting from the formation of interlayers, besides the thicker ZnS shell. Moreover, the effect relates to the halogen ions where I- presents more obvious enhancement than Br- and Cl- , owing to their different ability to coordinate with In dangling bonds, which are inclined to form In-S and Sx -In-P1-x bonds. Further, the anion exchange under I- -rich environment causes a blue-shift of emission wavelength with shelling temperature increasing, unobserved in a Cl- - or Br- -rich environment. It contributes to the preparation of highly efficient blue emissive InP/ZnS QDs with emission wavelength of 473 nm, photoluminescence quantum yield of ≈50% and full width at half maximum of 47 nm.

White-Light GaN-µLEDs Employing Green/Red Perovskite Quantum Dots as Color Converters for Visible Light Communication.

GaN-based µLEDs with superior properties have enabled outstanding achievements in emerging micro-display, high-quality illumination, and communication applications, especially white-light visible light communication (WL-VLC). WL-VLC systems can simultaneously provide white-light solid-state lighting (SSL) while realizing high-speed wireless optical communication. However, the bandwidth of conventional white-light LEDs is limited by the long-lifetime yellow yttrium aluminum garnet (YAG) phosphor, which restricts the available communication performance. In this paper, white-light GaN-µLEDs combining blue InGaN-µLEDs with green/red perovskite quantum dots (PQDs) are proposed and experimentally demonstrated. Green PQDs (G-PQDs) and red PQDs (R-PQDs) with narrow emission spectrum and short fluorescence lifetime as color converters instead of the conventional slow-response YAG phosphor are mixed with high-bandwidth blue InGaN-µLEDs to generate white light. The communication and illumination performances of the WL-VLC system based on the white-light GaN-based µLEDs are systematically investigated. The VLC properties of monochromatic light (green/red) from G-PQDs or R-PQDs are studied in order to optimize the performance of the white light. The modulation bandwidths of blue InGaN-µLEDs, G-PQDs, and R-PQDs are up to 162 MHz, 64 MHz, and 90 MHz respectively. Furthermore, the white-light bandwidth of 57.5 MHz and the Commission Internationale de L'Eclairage (CIE) of (0.3327, 0.3114) for the WL-VLC system are achieved successfully. These results demonstrate the great potential and the direction of the white-light GaN-µLEDs with PQDs as color converters to be applied for VLC and SSL simultaneously. Meanwhile, these results contribute to the implementation of full-color micro-displays based on µLEDs with high-quality PQDs as color-conversion materials.

Cation Crosslinking-Induced Stable Copper Nanoclusters Powder as Latent Fingerprints Marker.

Luminescent copper nanoclusters (Cu NCs) have shown great potential in light-emitting devices (LEDs), chemical sensing, catalysis and biological fields. However, their practical use has been restricted by poor stability, and study on the stability of Cu NCs solid powder along with the mechanism is absent. In this study, stablized Cu NCs powder was first obtained by cation crosslinking method. Compared with the powder synthesized by solvent precipitation method, the stability of Cu NCs powder crosslinked by ionic inducer Ce3+ was enhanced around 100-fold. The storage time when the fluorescence intensity decreased to 85% (T85) was improved from 2 h to 216 h, which is the longest so far. The results of characterizations indicated that the aggregation structure was formed by the binding of Ce3+ with the capping ligands of Cu NCs, which helped in obtaining Ce-Cu NCs powder from aggregate precipitation in solution. Furthermore, this compact structure could avoid the destruction of ambient moisture resulting in long-lasting fluorescence and almost unchanged physical form. This demonstrated that phosphor, with excellent characteristics of unsophisticated synthesis, easy preservation and stable fluorescence, showed great potential in light sources, display technology and especially in latent fingerprints visualization on different substrates for forensic science.

Emission tuning of highly efficient quaternary Ag-Cu-Ga-Se/ZnSe quantum dots for white light-emitting diodes.

With the blooming development of zero-dimensional nanomaterials, I-III-VI alloying quantum dots (QDs) with outstanding photoelectrical properties have emerged to attract much attention as promising environmentally-friendly substitutions for conventional binary Cd-based QDs. In this work, a facile one-pot method was introduced to synthesize unreported quaternary Ag-Cu-Ga-Se/ZnSe (ACGSe/ZnSe) QDs. A relatively high photoluminescence quantum yield (PL QY) of 71.9% and a tunable emission from 510 to 620 nm were successfully achieved. We explored the roles of alloying compositions in ACGSe/ZnSe QDs, inferring that increased Ag proportion would not only lower the Vdefect level which leads to the blue shift of emission, but also slow the ZnSe shelling process owing to the larger lattice distortion. At last, the white light-emitting diodes (WLEDs) were fabricated with ACGSe/ZnSe QDs as the conversion layer, indicating that the as-prepared QDs are a promising candidate for further applications.

Dual-emission of silicon nanoparticles encapsulated lanthanide-based metal-organic frameworks for ratiometric fluorescence detection of bacterial spores.

Dipicolinic acid (DPA) is employed as a significant biomarker to detect Bacillus anthracis, which can do serious damages to the health of human beings. Hence, it is crucial to develop a fast and highly efficient strategy for DPA monitoring. In this work, based on silicon nanoparticles (Si NPs) and terbium metal-organic frameworks (Tb-MOFs), a hybrid structure (Si NPs/Tb-MOFs) as a novel dual-emitting fluorescence probe was fabricated for ratiometric detection of DPA, where blue light-emitting Si NPs (Ex: 280 nm; Em: 422 nm) are encapsulated into green light-emitting Tb-MOFs (Ex: 280 nm; Em: 547 nm). The optical properties and chemical composition of the as-obtained Si NPs/Tb-MOFs were characterized in detail. The Si NPs/Tb-MOFs probe not merely possesses the merits of a facile synthesis method but also is an excellent fluorescence probe. The response time towards DPA is less than 30 s, revealing that the process of detecting DPA can be completed in such a short time. The limit of detection for DPA is 5.3 nM, which is four orders of magnitude lower than an infectious dosage of anthrax spores for human beings (60 µM). This dual-emitting Si NPs/Tb-MOFs probe with interference-free and self-calibrating properties may be a potential candidate for further development in medical diagnosis. Graphical abstract.

Facile Synthesis and Optical Properties of CsPbX3/ZIF-8 Composites for Wide-Color-Gamut Display.

All-inorganic CsPbX3 (X = Cl, Br, and I) perovskite quantum dots (QDs), an emerging type of luminescent materials, have drawn extensive attention in recent years. However, the amelioration of their stability is becoming a critical issue. Herein, we present a facile and efficient approach to prepare novel perovskite QDs/metal-organic frameworks (CsPbX3/ZIF-8) composites under ambient-atmospheric conditions. The obtained composites exhibit better properties including high photoluminescence (PL) quantum yields (QYs) (41.2% for green and 34.8% for red), narrow-band emission (20 nm for green and 31 nm for red), and enhanced stability in comparison to bare QDs. Furthermore, their application in a remote-type white-light-emitting device was explored and a wide color gamut (~137% of the National Television System Committee standard) was achieved, verifying that these novel luminescent composites have great prospect in backlight display application.