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

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.

Optoelectronic Properties of Nitrogen-Doped Hexagonal Graphene Quantum Dots: A First-Principles Study

Graphene quantum dots have been widely studied owing to their unique optical, electrical, and optoelectrical properties for various applications in solar devices. Here, we investigate the optoelectronic properties of hexagonal and nitrogen-doped graphene quantum dots using the first-principles method. We find that doping nitrogen atoms to hexagonal graphene quantum dots results in a significant red shift toward the visible light range as compared to that of the pristine graphene quantum dots, and the doped nitrogen atoms also induce a clear signature of anisotropy of the frontier orbitals induced by the electron correlation between the doped nitrogen atoms and their adjacent carbon atoms. Moreover, time-dependent density functional theory calculations with the M06-2X functional and 6-311++G(d,p) basis set reproduce well the experimental absorption spectra reported recently. These results provide us with a novel approach for more systematic investigations on next-generation solar devices with assembled quantum dots to improve their light selectivity as well as efficiency.

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.

Colloidal Zn3X2 (X = P, As) quantum dots with metal salts and their transformation into (InyZn1-y)3X2via cation-exchange reactions

We synthesized uniform Zn₃X₂ (X = P, As) quantum dots (QDs) for the first time using a stable, environmentally friendly zinc precursor instead of an organometallic precursor such as Me₂Zn or Et₂Zn, and controlled the QD size from about 2.0 nm to 6.0 nm. Moreover, tetragonal Zn₃P₂ and Zn₃As₂ QDs were transformed into zinc blende (In_yZn_1-y)₃P₂ and (In_yZn_1-y)₃As₂ QDs via the In³⁺ cationic-exchange reaction. To ensure the cation exchange reaction, we controlled reaction conditions, and confirmed it with various analytical methods. The replacement of Zn²⁺ by In³⁺ in the Zn₃X₂ QDs did not lead to changes in the particle size, but altered the optical properties and structure. In addition, we presented Cd₃P₂ and Cd₃As₂, which have the same tetragonal structure as the Zn₃X₂ QDs, through the same cationic exchange reaction.

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.