Engineering Brightness Matched Indium Phosphide Quantum Dots

Organoborane Se and Te Precursors for Controlled Modulation of Reactivity in Nanomaterial Synthesis

To exploit the distinctive optoelectrical properties of nanomaterials, precise control over the size, morphology, and interface structure is essential. Achieving a controlled synthesis demands precursors with tailored reactivity and optimal reaction temperatures. Here, we introduce organoborane-based selenium and tellurium precursors borabicyclononane-selenol (BBN-SeH) and tellurol (BBN-TeH). The reactivity of these precursors can be modified by commercially available additives, covering a wide range of intermediate reactivity and filling significant reactivity gaps in existing options. By allowing systematic adjustment of growth conditions, they achieve the controlled growth of quantum dots of various sizes and materials. Operating via a surface-assisted conversion mechanism, these precursors rely on surface coordination for activation and undergo quantitative deposition on coordinating surfaces. These properties allow precise control over the radial distribution and density of different chalcogenide atoms within the nanoparticles. Diborabicyclononanyl selane ((BBN)2Se), an intermediate from the BBN-SeH synthesis, can also serve as a selenium precursor. While BBN-SeH suppresses nucleation, (BBN)2Se exhibits efficient nucleation under specific conditions. By leveraging these distinct activation behaviors, we achieved a controlled synthesis of thermally stable nanoplates with different thicknesses. This study not only bridges critical reactivity gaps but also provides a systematic methodology for precise nanomaterial synthesis.

Construction of a stable fluorescent sensor based on CsPbBr3/CdS core/shell quantum dots for selective and sensitive detection of tetracycline in ethanol

The weakly bound organic ligand shells around perovskite quantum dots (QDs) are easily decomposed and cannot provide sufficient stability in polar solvents, which greatly obstructs their applications in sensing. Herein, a fluorescent sensor based on CsPbBr3/CdS core/shell QDs was developed for the detection of tetracycline (TC) in the polar solvent-ethanol. Pristine CsPbBr3 QDs were treated with cadmium diethyldithiocarbamate (Cd(DDTC)2) to form a shell on the surface at 110 °C, while extra oleylammonium bromide (OAmBr) was added to inhibit the phase transformation of CsPbBr3 into a Cs4PbBr6 impurity phase during high-temperature processing. And finally CsPbBr3/CdS core/shell QDs were successfully synthesized. The capping with the CdS inorganic shell remediated surface defects and improved the stability in ethanol without affecting the emission properties of the parent CsPbBr3 QDs. The results showed that the fluorescent sensor detected TC in the range of 0.05-25 μM with a low detection limit of 22.6 nM, whereas it had high selectivity and anti-interference ability for TC. And the fluorescence quenching mechanism of the sensor was mainly photoinduced electron transfer between TC and CsPbBr3/CdS QDs. Our research provides a unique way to improve the stability of perovskite QDs in polar solvents and applications in fluorescence detection.

Enhanced Charge Transfer from Coinage Metal Doped InP Quantum Dots

This paper describes coinage-metal-doped InP quantum dots (QDs) as a platform for enhanced electron transfer to molecular acceptors relative to undoped QDs. A synthetic strategy is developed to prepare doped InP/ZnSe QDs. First-principles DFT calculations show that Ag+ and Cu+ dopants localize photoexcited holes while leaving electrons delocalized. This charge carrier wave function modulation is leveraged to enhance electron transfer to molecular acceptors by up to an order of magnitude. Examination of photoluminescence quenching data suggests that larger electron acceptors, such as anthraquinone and methyl viologen, bind to the QD surface in two ways: by direct adsorption to the surface and by adsorption following displacement of a weakly bound surface cation-ligand complex. Reactions with larger acceptors show the greatest increases in electron transfer between doped and undoped quantum dots, while smaller acceptors show smaller enhancements. Specifically, benzoquinone shows the smallest, followed by naphthoquinone and then methyl viologen and anthraquinone. These results demonstrate the benefits of dopant-induced excited-state carrier localization on photoinduced charge transfer and highlight design principles for improved implementation of quantum dots in photoredox catalysis.

Surface Chemistry Dictates the Enhancement of Luminescence and Stability of InP QDs upon c-ALD ZnO Hybrid Shell Growth

Indium phosphide quantum dots (InP QDs) are a promising example of Restriction of Hazardous Substances directive (RoHS)-compliant light-emitting materials. However, they suffer from low quantum yield and instability upon processing under ambient conditions. Colloidal atomic layer deposition (c-ALD) has been recently proposed as a methodology to grow hybrid materials including QDs and organic/inorganic oxide shells, which possess new functions compared to those of the as-synthesized QDs. Here, we demonstrate that ZnO shells can be grown on InP QDs obtained via two synthetic routes, which are the classical sylilphosphine-based route and the more recently developed aminophosphine-based one. We find that the ZnO shell increases the photoluminescence emission only in the case of aminophosphine-based InP QDs. We rationalize this result with the different chemistry involved in the nucleation step of the shell and the resulting surface defect passivation. Furthermore, we demonstrate that the ZnO shell prevents degradation of the InP QD suspension under ambient conditions by avoiding moisture-induced displacement of the ligands from their surface. Overall, this study proposes c-ALD as a methodology for the synthesis of alternative InP-based core@shell QDs and provides insight into the surface chemistry that results in both enhanced photoluminescence and stability required for application in optoelectronic devices and bioimaging.

Type-I CdSe@CdS@ZnS Heterostructured Nanocrystals with Long Fluorescence Lifetime

Conventional single-component quantum dots (QDs) suffer from low recombination rates of photogenerated electrons and holes, which hinders their ability to meet the requirements for LED and laser applications. Therefore, it is urgent to design multicomponent heterojunction nanocrystals with these properties. Herein, we used CdSe quantum dot nanocrystals as a typical model, which were synthesized by means of a colloidal chemistry method at high temperatures. Then, CdS with a wide band gap was used to encapsulate the CdSe QDs, forming a CdSe@CdS core@shell heterojunction. Finally, the CdSe@CdS core@shell was modified through the growth of the ZnS shell to obtain CdSe@CdS@ZnS heterojunction nanocrystal hybrids. The morphologies, phases, structures and performance characteristics of CdSe@CdS@ZnS were evaluated using various analytical techniques, including transmission electron microscopy, X-ray diffraction, UV-vis absorption spectroscopy, fluorescence spectroscopy and time-resolved transient photoluminescence spectroscopy. The results show that the energy band structure is transformed from type II to type I after the ZnS growth. The photoluminescence lifetime increases from 41.4 ns to 88.8 ns and the photoluminescence quantum efficiency reaches 17.05% compared with that of pristine CdSe QDs. This paper provides a fundamental study and a new route for studying light-emitting devices and biological imaging based on multicomponent QDs.

Strategies to Extend the Lifetime of Perovskite Downconversion Films for Display Applications

Metal halide perovskite nanocrystals (PeNCs) have outstanding luminescent properties that are suitable for displays that have high color purity and high absorption coefficient; so they are evaluated for application as light emitters for organic light-emitting diodes, light-converters for downconversion displays, and future near-eye augmented reality/virtual reality displays. However, PeNCs are chemically vulnerable to heat, light, and moisture, and these weaknesses must be overcome before devices that use PeNCs can be commercialized. This review examines strategies to overcome the low stability of PeNCs and thereby permit the fabrication of stable downconversion films, and summarizes downconversion-type display applications and future prospects. First, methods to increase the chemical stability of PeNCs are examined. Second, methods to encapsulate PeNC downconversion films to increase their lifetime are reviewed. Third, methods to increase the long-term compatibility of resin with PeNCs, and finally, how to secure stability using fillers added to the resin are summarized. Fourth, the method to manufacture downconversion films and the procedure to evaluate their reliability for commercialization is then described. Finally, the prospects of a downconversion system that exploits the properties of PeNCs and can be employed to fabricate fine pixels for high-resolution displays and for near-eye augmented reality/virtual reality devices are explored.

InP quantum dots: Stoichiometry regulates carrier dynamics

The optical properties of non-toxic indium phosphide (InP) quantum dots (QDs) are impinged by the existence of characteristic deep trap states. Several surface engineering strategies have been adopted to improve their optical quality, which has promoted the use of InP QDs for various technological applications. An antithetical approach involves the effective utilization of the deep trap states in InP QDs to modulate back electron transfer rates. Here, we explore the influence of the core-size of InP on their In-to-P stoichiometry and charge transfer dynamics when bound to an acceptor molecule, decyl viologen (DV2+). The mechanism of interaction of InP and DV2+ based on the quenching sphere model established the presence of (i) a 1:1 complex of DV2+ bound on InP and (ii) immobile quenchers in the quenching sphere, depending on the concentration of DV2+. While the forward electron transfer rates from photoexcited InP to bound DV2+ does not substantially vary with an increase in core size, the back electron transfer rates are found to be retarded. Findings from inductively coupled plasma-optical emission spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS) reveal that the In to P ratio is higher for QDs with larger core size, which further brings about increased carrier trapping and a decreased rate of charge recombination. Furthermore, long-lived charge-separated states in DV2+ bound to InP, extending to hundreds of milliseconds, are obtained by varying the number of DV2+ in the quenching sphere of the QDs.

Encapsulation of Cadmium-Free InP/ZnSe/ZnS Quantum Dots in Poly(LMA-co-EGDMA) Microparticles via Co-flow Droplet Microfluidics

Quantum dots (QDs) are semiconductor nanocrystals that are used in optoelectronic applications. Most modern QDs are based on toxic metals, for example Cd, and do not comply with the European Restriction of Hazardous Substances regulation of the European Union. Latest promising developments focus on safer QD alternatives based on elements from the III-V group. However, the InP-based QDs lack an overall photostability under environmental influences. One design path of achieving stability is through encapsulation in cross-linked polymer matrices with the possibility to covalently link the matrix to surface ligands of modified core-shell QDs. The work focuses on the formation of polymer microbeads suitable for InP-based QD encapsulation, allowing for an individual protection of QDs and an improved processibility via this particle-based approach. For this, a microfluidic based method in the co-flow regime is used that consists of an oil-in-water droplet system in a glass capillary environment. The generated monomer droplets are polymerized in-flow into poly(LMA-co-EGDMA) microparticles with embedded InP/ZnSe/ZnS QDs using a UV initiation. They demonstrate how a successful polymer microparticle formation via droplet microfluidics produces optimized matrix structures leading to a distinct photostability improvement of InP-based QDs compared to nonprotected QDs.

Deep Blue and Highly Emissive ZnS-Passivated InP QDs: Facile Synthesis, Characterization, and Deciphering of Their Ultrafast-to-Slow Photodynamics

InP-based quantum dots (QDs) are an environment-friendly alternative to their heavy metal-ion-based counterparts. Herein we report a simple procedure for synthesizing blue emissive InP QDs using oleic acid and oleylamine as surface ligands, yielding ultrasmall QDs with average sizes of 1.74 and 1.81 nm, respectively. Consecutive thin coating with ZnS increased the size of these QDs to 4.11 and 4.15 nm, respectively, alongside a significant enhancement of their emission intensities centered at ∼410 nm and ∼430 nm, respectively. Pure phase synthesis of these deep-blue emissive QDs is confirmed by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Armed with femtosecond to millisecond time-resolved spectroscopic techniques, we decipher the energy pathways, reflecting the effect of successive ZnS passivation on the charge carrier (electrons and holes) dynamics in the deep-blue emissive InP, InP/ZnS, and InP/ZnS/ZnS QDs. Successive coating of the InP QDs increases the intraband relaxation times from 200 to 700 fs and the lifetime of the hot electrons from 2 to 8 ps. The lifetime of the cold holes also increase from 1 to 4 ps, and remarkably, the Auger recombination escalates from 15 to 165 ps. The coating also drastically decreases the quenching by the molecular oxygen of the trapped charge carriers at the surfaces of the QDs. Our results provide clues to push further the emission of InP QDs into more energetically spectral regions and to increase the fluorescence quantum yield, targeting the construction of efficient UV-emissive light-emitting devices (LEDs).