Indium Phosphide Quantum Dots: Advancements in Properties, Synthesis, and Applications - Nanografi

Indium Phosphide Quantum dots, which are made of colloidal quantum dots, have garnered a lot of attention over the past 20 years as a potentially safer substitute for cadmium-based quantum dots. 

They have been able to synthesize a variety of compositions, heterojunctions, dopants, and ligands with short emission line widths, excellent quantum yields close to unity, and spectrum tunability from blue to near-infrared thanks to advancements in their colloidal synthesis processes. Additionally, it has a higher covalency than cadmium chalcogenides, enhancing optical stability. In a variety of applications, including solar cells with significant commercial promise, luminescent solar concentrators (LSCs), and light-emitting diodes, modern indium phosphide quantum dots have proven to perform better than conventional materials. At Nanografi, we firmly believe that quantum dots hold the key to unlocking endless possibilities across a wide range of applications. Contact us as we reshape industries, redefine performance benchmarks, and pave the way for a greener, more efficient tomorrow.

Introduction

Non-toxic nanomaterials called indium phosphide quantum dots (InP QDs) have potential uses in the domains of photocatalysis and optoelectronics. Although it is well known that InP QDs require post-synthetic processing to increase their photoluminescence quantum efficiencies (PLQEs) and device performances, the mechanisms are still not fully understood. Here, we thoroughly analyze the dynamics of photogenerated carriers in InP QDs and how they are impacted by two widely used passivation techniques: HF (Hydrofluoric Acid) treatment and the development of a heterostructure shell (ZnS in this study).

HF Treatment and PLQE Enhancement

By eliminating an intrinsic rapid hole trapping channel (h, non = 3.4 1 ns) in the untreated InP QDs, the HF treatment is found to improve the PLQE up to 16–20% while having minimal impact on the dynamics of the band-edge electron decay τe = 26–32 ns).

Heterostructure Shell and PLQE Enhancement

By passivating the electron and hole traps in InP QDs, the expansion of the ZnS shell, on the other hand, is demonstrated to increase the PLQE by up to 35–40%. This results in both a long band-edge electron lifetime (e > 120 ns) and a slower hole-trapping lifetime (h, non > 45 ns).

Biomedical Applications of Cationic InP/ZnS QDs

In nanobiotechnology, Indium Phosphide Quantum Dots (InP QDs) have become a viable substitute for hazardous metal ion-based QDs. InP QDs must be able to generate cationic surface charge to reach their full potential in biological applications while maintaining stability and biocompatibility. To overcome this difficulty, a place exchange mechanism for making cationic InP/ZnS QDs was created. InP/ZnS QDs in biofluids receive the crucial permanent positive charge and stability from the quaternary ammonium group.

Bioimaging and Light-Induced Resonance Energy Transfer

In cationic InP/ZnS QDs, the two key QD features of bioimaging and light-induced resonance energy transfer have been successfully shown. The cationic InP/ZnS QDs inside cells offer excellent candidates for optical probes for cellular imaging due to their low cytotoxicity and stable photoluminescence. Under physiological circumstances, an effective resonance energy transfer (E 60%) between the cationic InP/ZnS QD donor and anionic dye acceptor is observed. Strong ground state complex formation between the anionic dye and the cationic InP/ZnS QDs is confirmed by a large bimolecular quenching constant and a linear Stern-Volmer plot.

Surface Passivation and Multiexciton Lifetimes

By merely changing the particle sizes, colloidal quantum-confined nanocrystals, especially spherical quantum dots (QDs), can demonstrate a broad tunability of their band gaps, multiexciton lifetimes, and band-edge positions, enabling their applications in lasing, light-emitting diodes (LEDs), and solar fuel generation. The creation of surface passivation techniques that increase the lifetime of both single and multiple exciton states is crucial. The first passivation technique involved subjecting InP quantum dots (QDs) to post-synthetic treatment with HF while simultaneously illuminating them. The second passivation technique involves growing an inorganic shell around the InP core.

Auger Recombination Processes and InP QDs

Under operational conditions, many exciton states are involved in several optoelectronic applications of QDs, such as lasing and LED. Auger recombination (AR) activities, where the nonradiative decay of one exciton simultaneously drives another exciton or carrier into its higher energetic state, are the predominant energy loss mechanism in the multiexciton regime. Surface passivation's effects on multiexciton states in InP QDs have thus far been poorly described and comprehended. The short biexciton lifespan is not significantly affected by HF treatment, but the formation of a ZnS shell (0.2 nm) surrounding the InP core can provide a striking 20-fold increase in the biexciton lifetime in InP QDs.

Core-Shell High-Luminosity Semiconductor Crystals

The core-shell high-luminosity semiconductor crystals known as Indium Phosphide/Zinc Sulfide (InP/ZnS) Quantum Dots have an inner core of Indium Phosphide and an outer core of Zinc Sulfide. Oleylamine ligands can be used to stabilize InP/ZnS quantum dots, and they are soluble in a variety of organic solvents, including toluene. These quantum dots have the unexpected virtue of having an extremely narrow emission spectrum (Gaussian Distribution) that is directly proportional to the particle's size, with spectra emissions ranging from 530 nanometers (nm) to 650 nanometers (nm) wavelengths.

Synthesis, Properties, and Applications of Indium Phosphide Quantum Dots

Modern InP QDs have excelled in numerous applications with the potential for commercialization because of their appealing optical and electrical features. Due to their inherent lack of toxicity and high photoluminescence, colloidal InP quantum dots (QDs) have been regarded as one of the most promising choices for display and biolabeling applications. They are widely used in display technologies, light-emitting diodes (LEDs), biomedical applications like bioimaging, electronic devices, and solar cells.

Electrical and Optical Properties of InP QDs and Their Applications

Due to their electrical and optical properties, InP QDs find applications in various fields. They are used in light-emitting diodes (LEDs) for efficient and vibrant color displays. In biomedical applications, such as bioimaging, InP QDs offer excellent photoluminescence and low toxicity, making them suitable for precise imaging and diagnostics. Electronic devices benefit from the unique optical properties of InP QDs for improved performance and functionality. Additionally, InP QDs are utilized in solar cells to enhance light absorption and energy conversion efficiency.

In conclusion, InP quantum dots (QDs) exhibit favorable properties, including a large excitonic Bohr radius, high carrier mobility, high absorption coefficient, wide color tunability, and low toxicity. Through advancements in synthesis techniques, colloidal InP QDs have been successfully created with high quantum yield and color purity. These QDs have found extensive applications in areas such as display technology, bioimaging, electronics, and solar energy. Challenges in achieving uniform size distribution and understanding the development mechanisms of InP QDs continue to be areas of active research. However, the unique properties of InP QDs make them a promising choice for various technological applications.

Biosensing and Bioimaging Applications of Indium Phosphide Quantum Dots

Indium phosphide quantum dots (InP QDs) have emerged as a promising class of nanomaterials for biosensing and bioimaging applications. These nanocrystals possess unique optical properties, including size-dependent emission wavelengths and high photoluminescence quantum yields, making them highly desirable for biological imaging. InP QDs can be functionalized with biomolecules such as antibodies, peptides, or DNA probes, allowing specific targeting of cellular structures or biomarkers. Their small size and biocompatibility enable efficient cellular uptake and minimize potential cytotoxicity. In bioimaging, InP QDs exhibit excellent brightness, photostability, and long fluorescence lifetimes, facilitating high-resolution imaging and tracking of cellular processes in real-time. Moreover, their wide absorption spectrum enables multi-color imaging and multiplexed detection of various biological targets simultaneously. With ongoing research and development, InP QDs hold great promise for advancing biosensing and bioimaging techniques, offering new possibilities for understanding complex biological systems and improving diagnostics and therapeutics in biomedical applications.

For further insight on Quantum Dots, you can check out our blog post here.

Advantages and Synthesis of InP Quantum Dots

The advantages of InP QDs over traditional Cd/Pb-based QDs for usage in practical settings are their high absorption coefficient, wide color tunability, and low toxicity. With the aid of organic ligands, small-sized colloidal InP QDs have been created over the past 20 years thanks to improvements in wet-chemistry techniques. The QYs of InP QDs are driven to almost unity with only moderate color purity by careful selection of synthesis methods and precursor materials in conjunction with surface passivation.

Unique Synthetic Method and Blue Photoluminescence Emission

Creating high-quality blue-emitting InP QDs with a uniform size distribution is still difficult because of the unpredictable nucleation and growth that occur during the synthesis of InP. Here, we use a unique synthetic method to create InP/ZnS core/shell QDs that emit blue light with the help of copper cations. The research shows that the hexagonal Cu3-xP nanocrystals formed by the copper ions and phosphorus precursor could compete with the formation of indium phosphide quantum dots (InP QDs), resulting in smaller InP QDs with blue photoluminescence emission. The produced InP/ZnS core/shell QDs emit vivid blue light at a wavelength of 425 nm with a photoluminescence quantum yield of about 25%, which is the shortest wavelength emission for InP QDs to date.

Challenges in Size Distribution and Reactivity Regulation

InP QDs' broad emission profile is a drawback, and methods to synthesize monodisperse InP QDs have been investigated since the broad emission peak may be primarily caused by an inhomogeneous size distribution. Some researchers have tried to regulate the reactivity of molecular precursors to restrict the size distribution of InP QDs. Tris(trimethylgermyl) phosphine, phosphine (PH3), amino phosphine, and other less reactive precursors have taken the place of the commonly employed tris(trimethylsilyl)phosphine ((TMS)3P), which is too reactive and results in inseparable nucleation and growth phases. However, the size diversity of the generated InP QDs was not significantly reduced by the employment of these several chemical precursors. 

Emission Characteristics and Development Mechanisms of InP Quantum Dots 

As of now, InP QDs' emission characteristics are still higher than those of Cd-based QDs. The narrowest ensemble emission peak of InP QDs observed thus far is a 35 nm FWHM, whereas the ensemble CdSe emission peak can be as small as 20 nm. The wide FWHM of InP QDs spurs investigation into the mechanism underlying InP QD development. The stages of nucleation and development could be crucial factors in determining the homogeneity of InP QDs. Nonclassical growth mechanisms have recently been identified since the traditional LaMer model of nucleation and growth kinetics does not completely account for the formation of nanomaterials. The development of intermediate states, also known as MSCs (molecular nanoclusters) or atomically precise nanoclusters, is the process by which InP QDs grow. Small nanocrystals with a diameter of 2 nm or less are considered to be nanoclusters. These MSCs are highly stable structures that are only 2 nm in size. The wavelength of the persistent lowest energy electronic transition (LEET) is typically used to identify MSCs. The narrow bandwidth of the LEET results from the production of single-sized products, distinguishing the optical properties of MSCs from generic QDs. However, managing MSCs is quite challenging, and their production and dissolution can slow down the pace of QD formation. The high thermal stability of InP MSCs has been observed to influence the growth of InP QDs. InP MSCs have been detected as intermediates during the formation of InP QDs, and their mass has been observed up to 300 °C. Further research and isolation of InP MSCs have been conducted to better understand the development mechanisms of InP QDs.

Conclusion

In summary, Indium Phosphide Quantum Dots (InP QDs) have emerged as a highly promising nanomaterial with extensive applications in biosensing and bioimaging. Their unique properties, including high quantum yield, tunable emission spectrum, and excellent photostability, make them valuable tools for developing sensitive fluorescence biosensors. The development of surface passivation techniques, such as HF treatment and heterostructure shell formation, has significantly enhanced the photoluminescence quantum efficiencies of InP QDs. In biomedical applications, cationic InP/ZnS QDs have demonstrated excellent biocompatibility and have shown potential as optical probes for bioimaging and light-induced resonance energy transfer. Additionally, InP QDs exhibit favorable electrical and optical properties, making them suitable for applications in light-emitting diodes, electronic devices, and solar cells. Despite challenges in achieving uniform size distribution and understanding their development mechanisms, InP QDs hold great promise for advancing biosensing and bioimaging techniques, contributing to the progress of biomedical research and diagnostics. By offering state-of-the-art technologies and utilizing top-notch materials, Nanografi provides innovative solutions that empower your projects and elevate your business performance. Choose Nanografi products to unlock your full potential and drive unprecedented success.

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