Emissive ZnO@Zn3 P2 nanocrystals: synthesis, optical, and optoelectrochemical properties

Heterostructure seed-mediated synthesis of zinc phosphide quantum dots for bright band-edge emission

This study explores the synthesis of colloidal zinc phosphide quantum dots (QDs) by a novel In(Zn)P cluster seed-mediated approach, addressing the challenge of achieving low-cost, high-quality, nontoxic QDs suitable for optoelectronic applications. By intentionally limiting the amount of In precursor added to a hot solvent containing Zn and P precursors, In-rich In(Zn)P cluster seeds were formed. Subsequently, these clusters served as seeds for the growth of zinc phosphide nanocrystals, effectively using the remaining Zn and P precursors for further crystal growth. The synthesized QDs exhibited a tetragonal-like Zn3P2 structure and exceptional optical properties, including band-edge photoluminescence (PL) emission under ambient conditions. A ZnS shell was applied to further enhance the PL intensity, achieving a PL quantum yield of 40% and an average PL decay lifetime of 74 ns, while significantly improving the stability of the QDs. Temperature-dependent PL spectroscopy revealed significant resistance to thermal quenching with an exciton dissociation energy of 62 meV, underscoring the potential of this approach for advancing the field of optoelectronics. This method provides a pathway to fabricate zinc phosphide-based QDs with controlled optical properties and highlights the effective use of earth-abundant materials in the development of environmentally benign photonic materials.

Cd3P2/Zn3P2 Core-Shell Nanocrystals: Synthesis and Optical Properties

II-V semiconductor nanocrystals such as Cd₃P₂ and Zn₃P₂ have enormous potential as materials in next-generation optoelectronic devices requiring active optical properties across the visible and infrared range. To date, this potential has been unfulfilled due to their inherent instability with respect to air and moisture. Core-shell system Cd₃P₂/Zn₃P₂ is synthesized and studied from structural (morphology, crystallinity, shell diameter), chemical (composition of core, shell, and ligand sphere), and optical perspectives (absorbance, emission-steady state and time resolved, quantum yield, and air stability). The improvements achieved by coating with Zn₃P₂ are likely due to its identical crystal structure to Cd₃P₂ (tetragonal), highlighting the key role crystallographic concerns play in creating cutting edge core-shell NCs.

Synthesis of luminescent core/shell α-Zn3P2/ZnS quantum dots

Metal chalcogenide nanoparticles offer vast control over their optoelectronic properties via size, shape, composition, and morphology which has led to their use across fields including optoelectronics, energy storage, and catalysis. While cadmium and lead-based nanocrystals are prevalent in applications, concerns over their toxicity have motivated researchers to explore alternate classes of nanomaterials based on environmentally benign metals such as zinc and tin. The goal of this research is to identify material systems that offer comparable performance to existing metal chalcogenide systems from abundant, recyclable, and environmentally benign materials. With band gaps that span the visible through the infrared, II-V direct band gap semiconductors such as tetragonal zinc phosphide (α-Zn3P2) are promising candidates for optoelectronics. To date, syntheses of α-Zn3P2 nanoparticles have been hindered because of the toxicity of zinc and phosphorus precursors, surface oxidation, and defect states leading to carrier trapping and low photoluminescence quantum yield. This work reports a colloidal synthesis of quantum confined α-Zn3P2 nanoparticles from common phosphorus precursor tris(trimethylsilyl)phosphine and environmentally benign zinc carboxylates. Shelling of the nanoparticles with zinc sulfide is shown as a method of preventing oxidation and improving the optical properties of the nanoparticles. These results show a route to stabilizing α-Zn3P2 nanoparticles for optoelectronic device applications.

Sustainable quantum dot chemistry: effects of precursor, solvent, and surface chemistry on the synthesis of Zn3P2 nanocrystals

The quest of exploring alternative materials for the replacement of toxic cadmium- and lead-based quantum dots (QDs) is necessary for envisaging a sustainable future but remains highly challenging. Tackling this issue, we present the synthesis of Zn3P2 nanocrystals (NCs) of unprecedented quality. New, reactive zinc precursors yield highly crystalline, colloidally stable particles, exhibiting oxide-free surfaces, size tunability and outstanding optical properties relative to previous reports of zinc phosphide QDs.

Facile synthesis of a hexanuclear zinc-acetato-trimethylsilylphosphinidene cluster: a single-source precursor to Zn3P2 nanoparticles

The selective synthesis of the zinc-acetato-phosphinidene cluster [Zn₆(μ₃-PSiMe₃)₄(OAc)₄(NC₅H₅)₅] 1 is presented. The cluster serves as a stable, single-source precursor to yield soluble zinc phosphide nanoparticles via P-Si bond activation and AcOSiMe₃ elimination when heated in oleylamine or other donor solvents.

Chemical Synthesis and Applications of Colloidal Metal Phosphide Nanocrystals

Colloidal nanocrystals (NCs) have emerged as promising materials in optoelectronic devices and biological imaging application due to their tailorable properties through size, shape, and composition. Among these NCs, metal phosphide is an important class, in parallel with metal chalcogenide. In this review, we summarize the recent progress regarding the chemical synthesis and applications of colloidal metal phosphide NCs. As the most important metal phosphide NCs, indium phosphide (InP) NCs have been intensively investigated because of their low toxicity, wide and tunable emission range from visible to the near-infrared region. Firstly, we give a brief overview of synthetic strategies to InP NCs, highlighting the benefit of employing zinc precursors as reaction additive and the importance of different phosphorus precursors to improve the quality of the InP NCs, in terms of size distribution, quantum yield, colloidal stability, and non-blinking behavior. Next, we discuss additional synthetic techniques to overcome the issues of lattice mismatch in the synthesis of core/shell metal phosphide NCs, by constructing an intermediate layer between core/shell or designing a shell with gradient composition in a radial direction. We also envision future research directions of InP NCs. The chemical synthesis of other metal phosphide NCs, such as II-V metal phosphide NCs (Cd3P2, Zn3P2) and transition metal phosphides NCs (Cu3P, FeP) is subsequently introduced. We finally discuss the potential applications of colloidal metal phosphide NCs in photovoltaics, light-emitting diodes, and lithium ion battery. An overview of several key applications based on colloidal metal phosphide NCs is provided at the end.

II3 V2 (II: Zn, Cd; V: P, As) Semiconductors: From Bulk Solids to Colloidal Nanocrystals

II₃ V₂ semiconductors have become increasingly popular for a variety of applications including solar light harvesting, near-IR imaging, and low energy light detection. The bulk physical and electronic structure of these materials is highlighted, followed by an in-depth survey on progress in synthesizing these semiconductors as colloidal nanocrystals. Interestingly, no universal synthetic approach has yet been developed to access all compounds within this family. A discussion on how the complex crystal structure of these materials translates to small domain sizes will highlight current challenges in the characterization of II₃ V₂ nanocrystals. Finally, potential avenues for further research will be proposed as a way to advance this field towards greater utilization in light harvesting applications.

Identifying short surface ligands on metal phosphide quantum dots

The control and understanding of the chemical and physical properties of quantum dots (QDs) demands detailed surface characterization. However, probing the immediate interface between the inorganic core and the ligands is still a major challenge. Here we show that using cross-polarization magic angle spinning (MAS) NMR, unprecedented information can be obtained on the surface ligands of Cd3P2 and InP QDs. The resonances of fragments which are usually challenging to detect like methylene or methyl near the surface, can be observed with our approach. Moreover, ligands such as hydroxyl and ethoxide which have so far never been detected at the surface can be unambiguously identified. This NMR approach is versatile, applicable to any phosphides and highly sensitive since it remains effective for identifying quantities as low as a few percent of surface atoms.

Zn₃P₂-Zn₃As₂ solid solution nanowires

Semiconductor alloy nanowires (NWs) have recently attracted considerable attention for applications in optoelectronic nanodevices because of many notable properties, including band gap tunability. Zinc phosphide (Zn3P2) and zinc arsenide (Zn3As2) belong to a unique pseudocubic tetragonal system, but their solid solution has rarely been studied. Here In this study, we synthesized composition-tuned Zn3(P1-xAsx)2 NWs with different crystal structures by controlling the growth conditions during chemical vapor deposition. A first type of synthesized NWs were single-crystalline and grew uniformly along the [110] direction (in a cubic unit cell) over the entire compositional range (0 ≤ x ≤ 1) explored. The use of an indium source enabled the growth of a second type of NWs, with remarkable cubic-hexagonal polytypic twinned superlattice and bicrystalline structures. The growth direction of the Zn3P2 and Zn3As2 NWs was also switched to [111] and [112], respectively. These structural changes are attributable to the Zn-depleted indium catalytic nanoparticles which favor the growth of hexagonal phases. The formation of a solid solution at all compositions allowed the continuous tuning of the band gap (1.0-1.5 eV). Photocurrent measurements were performed on individual NWs by fabricating photodetector devices; the single-crystalline NWs with [110] growth direction exhibit a higher photoconversion efficiency compared to the twinned crystalline NWs with [111] or [112] growth direction.

PbS/Cd₃P₂ quantum heterojunction colloidal quantum dot solar cells

Here, we demonstrated the quantum heterojunction colloidal quantum dot (CQD) solar cells employing the PbS CQDs/Cd3P2 CQDs architecture in which both the p-type PbS and n-type Cd3P2 CQD layers are quantum-tunable and solution-processed light absorbers. We synthesized well-crystallized and nearly monodispersed tetragonal Cd3P2 CQDs and then engineered their energy band alignment with the p-type PbS by tuning the dot size and hence the bandgap to achieve efficient light absorbing and charge separation. We further optimized the device through the Ag-doping strategy of PbS CQDs that may leverage an expanded depletion region in the n-layer, which greatly enhances the photocurrent. The resulting devices showed an efficiency of 1.5%.

Ternary synthesis of colloidal Zn3P2quantum dots

The synthesis and characterization of crystalline colloidal zinc phosphide quantum dots with observable excitonic transitions ranging between 424–535 nm (2.3–2.9 eV) are reported.

Solution-processed zinc phosphide (α-Zn3P2) colloidal semiconducting nanocrystals for thin film photovoltaic applications

Zinc phosphide (Zn3P2) is a promising earth-abundant material for thin film photovoltaic applications, due to strong optical absorption and near ideal band gap. In this work, crystalline zinc phosphide nanoparticles are synthesized using dimethylzinc and tri-n-octylphosphine as precursors. Transmission electron microscopy and X-ray diffraction data show that these nanoparticles have an average diameter of ∼8 nm and adopt the crystalline structure of tetragonal α-Zn3P2. The optical band gap is found to increase by 0.5 eV relative to bulk Zn3P2, while there is an asymmetric shift in the conduction and valence band levels. Utilizing layer-by-layer deposition of Zn3P2 nanoparticle films, heterojunction devices consisting of ITO/ZnO/Zn3P2/MoO3/Ag are fabricated and tested for photovoltaic performance. The devices are found to exhibit excellent rectification behavior (rectification ratio of 600) and strong photosensitivity (on/off ratio of ∼10(2)). X-ray photoelectron spectroscopy and ultraviolet photoemission spectroscopy analyses reveal the presence of a thin 1.5 nm phosphorus shell passivating the surface of the Zn3P2 nanoparticles. This shell is believed to form during the nanoparticle synthesis.