Highly Luminescent InP/GaP/ZnS Nanocrystals and Their Application to White Light-Emitting Diodes

Kim, Sung Woo; Kim, Tae-Hoon; Kang, Meejae; Kwak, Seong Kwon; Yoo, Tae Wook; Park, Lee Soon; Yang, Inho; Hwang, Sun‐Jin; Lee, Jung Eun; Kim, Seong Keun; Kim, Sang–Wook

doi:10.1021/ja210211z

Cited by 316 publications

(291 citation statements)

References 62 publications

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“…All aqueous solutions were prepared from Milli-Q water (Millipore). The Al 2 Te 3 lumps employed for the generation of H 2 Te were purchased from CERAC Inc. As for the QDs, we either used CdTe, [ 40 ] CdSe/ZnS [ 41 ] with an alloyed gradient shell, or core/shell/shell (CSS) InZnP/ GaP/ZnS [ 42 ] QDs, which were prepared according to previous publications.…”

Section: Methodsmentioning

confidence: 99%

Liquid–Liquid Diffusion‐Assisted Crystallization: A Fast and Versatile Approach Toward High Quality Mixed Quantum Dot‐Salt Crystals

Adam

Wang

Dubavik

et al. 2015

Adv Funct Materials

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2638www.MaterialsViews.com wileyonlinelibrary.com approaches, [ 15,16 ] effi ciency, [ 17,18 ] extending their spectral range [19][20][21] and environmental friendliness using less toxic materials [22][23][24] sparked industrial applications. Those started with the demonstration of a 40 in. display prototype presented by Samsung [ 25 ] and followed by the foundation of QD Vision, Inc., [ 26 ] whose QDs are now used in the latest series of Sony products. All of the mentioned applications require long-term stability of the QDs under various conditions including high temperatures as well as high intensity illumination. Packaging of the QDs within polymer or inorganic matrices is one way to address these issues, while improving the processability of the QDs at the same time. Commonly used polymers, such as polystyrene and poly(methylmethacrylate) [ 27 ] are relatively less stable and tight in comparison to their inorganic counterparts. Inorganic matrices on the other hand can incorporate the QDs directly from their melt, e.g., using the Czochralski approach, [ 28 ] coated as a thin fi lm directly on their surface [ 29,30 ] or, as recently developed by our group, grown as mixed crystals at ambient temperatures from a saturated salt solution. [ 31 ] Using this method, different types of QDs can be incorporated due to the low thermal stress and, by choosing the proper matrix-QD system, the photoluminescence quantum yields (PL-QYs) are enhanced upon incorporation. [ 32,33 ] Here, a new, fast, and versatile method for the incorporation of colloidal quantum dots (QDs) into ionic matrices enabled by liquid-liquid diffusion is demonstrated. QDs bear a huge potential for numerous applications thanks to their unique chemical and physical properties. However, stability and processability are essential for their successful use in these applications. Incorporating QDs into a tight and chemically robust ionic matrix is one possible approach to increase both their stability and processability. With the proposed liquid-liquid diffusion-assisted crystallization (LLDC), substantially accelerated ionic crystallization of the QDs is shown, reducing the crystallization time needed by one order of magnitude. This fast process allows to incorporate even the less stable colloids including initially oil-based ligandexchanged QDs into salt matrices. Furthermore, in a modifi ed two-step approach, the seed-mediated LLDC provides the ability to incorporate oilbased QDs directly into ionic matrices without a prior phase transfer. Finally, making use of their processability, a proof-of-concept white light emitting diode with LLDC-based mixed QD-salt fi lms as an excellent color-conversion layer is demonstrated. These fi ndings suggest that the LLDC offers a robust, adaptable, and rapid technique for obtaining high quality QD-salts.

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Section: Methodsmentioning

confidence: 99%

Liquid–Liquid Diffusion‐Assisted Crystallization: A Fast and Versatile Approach Toward High Quality Mixed Quantum Dot‐Salt Crystals

Adam

Wang

Dubavik

et al. 2015

Adv Funct Materials

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“…InP-based QDs are among the most investigated nontoxic Cd-free systems, owing to their comparable emission range. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] However, in terms of PL QY and PL stability they cannot yet compete with Cd-based QDs.…”

Section: Introductionmentioning

confidence: 99%

“…Although the addition of Zn to the synthesis of InP nanocrystals has become common practice in the last years, [11][12][13][14][15][16][17][21][22][23][24][25] very little has been reported on the actual role of the Zn. The few reports on this topic have focused on the effect on the optical properties, but structural aspects were not investigated.…”

Section: Introductionmentioning

confidence: 99%

Tuning the Lattice Parameter of In_xZn_yP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots

et al. 2016

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Colloidal quantum dots (QDs) show great promises as LED phosphors due to their tuneable narrow-band emission and ability to produce high-quality white light.Currently, the most suitable QDs for lighting applications are based on cadmium, which presents a toxicity problem for consumer applications. The most promising cadmiumfree candidate QDs are based on InP, but their quality lags much behind that of cadmium based QDs. This is not only because the synthesis of InP QDs is more challenging than that of Cd-based QDs, but also because the large lattice parameter of InP makes it difficult to grow an epitaxial, defect free shell on top of such material. Here we propose an original approach to overcome this problem by alloying InP nanocrystals with Zn 2+ ions, which enables the synthesis of In x Zn y P alloy QDs having lattice constant that can be tuned from 5.93 Å (pure InP QDs) down to 5.39 Å by simply varying the concentration of the Zn precursor. This lattice engineering allows for subsequent strainfree, epitaxial growth of a ZnSe z S 1-z shell with lattice parameters matching that of the core. We demonstrate, for a wide range of core and shell compositions (i.e. varying x, y and z), that the photoluminescence quantum yield is maximal (up to 60%) when lattice mismatch is minimal.3

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“…[62] In fact, typical InP core QDs without inorganic shell coating are known to exhibit exciton decay times in the order of several nanoseconds, which is comparable to that of the current blue-emitting InP@ZnS QDs. [69,70] This phenomenon was further reflected by the relative low QY of blue-emitting InP@ZnS QDs because the QY strongly depends on the degree of surface passivation (Table 1). …”

Section: Synthesis and Optical Properties Of Inp Quantum Dots Using Pmentioning

confidence: 99%

Large-Scale Synthesis of Highly Luminescent InP@ZnS Quantum Dots Using Elemental Phosphorus Precursor

et al. 2017

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Colloidal quantum dots can control the bandgap by controlling the particle size, and are capable of solution processing, which is cost competitive, and has a narrow half width of the emission wavelength.Using these characteristics, it is possible to utilize various kinds of LED, solar cell, and bio imaging.Among them, indium phosphide (InP) quantum dots have a bandgap capable of emitting light in the near-infrared region from the visible light region, and are less toxic to humans and the environment than cadmium-based quantum dots, and are attracting attention as next generation light emitting materials.However, the limited choice and high cost of P precursors have a negative impact on their practical applicability. In this work, I report the large-scale synthesis of highly luminescent InP@ZnS QDs from an elemental P precursor (P4), which was simply synthesized via the sublimation of red P powder. The size of the InP QDs was controlled by varying the reaction parameters such as the reaction time and temperature, and the type of In precursors. This way, the photoluminescence properties of the synthesized InP@ZnS QDs could be easily tuned across the entire visible range, while their quantum yield could be increased up to 60% via the optimization of reaction conditions. Furthermore, possible reaction pathways for the formation of InP QDs using the P4 precursor have been investigated with nuclear magnetic resonance spectroscopy and it was demonstrated that the direct reaction of P4 precursor with In precursor produces InP structures without the formation of intermediate species. The large-scale production of InP@ZnS QDs was demonstrated by yielding more than 6 g of QDs per onebatch reaction.In the case of InP using different precursor P except the Tris(Trimethylsilyl) phosphine ((TMS)3P) there has been a problem that the size distribution is poor. Two kinds of P precursors with different reactivities were used to separate the nucleation and growth processes and to induce growth along the Lamer mechanism to produce uniform particles. For this, (TMS)3P and DEAP were used as fast reacting P precursors, and P4 was used as a slow reacting P precursor. Through this, the possibility of uniform particle formation was observed. I strongly believe that the newly developed approach bears the potential to be widely used for manufacturing inexpensive high-quality QD emitters. Blank page Contents

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Highly Luminescent InP/GaP/ZnS Nanocrystals and Their Application to White Light-Emitting Diodes

Cited by 316 publications

References 62 publications

Liquid–Liquid Diffusion‐Assisted Crystallization: A Fast and Versatile Approach Toward High Quality Mixed Quantum Dot‐Salt Crystals

Liquid–Liquid Diffusion‐Assisted Crystallization: A Fast and Versatile Approach Toward High Quality Mixed Quantum Dot‐Salt Crystals

Tuning the Lattice Parameter of In_xZn_yP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots

Large-Scale Synthesis of Highly Luminescent InP@ZnS Quantum Dots Using Elemental Phosphorus Precursor

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Highly Luminescent InP/GaP/ZnS Nanocrystals and Their Application to White Light-Emitting Diodes

Cited by 316 publications

References 62 publications

Liquid–Liquid Diffusion‐Assisted Crystallization: A Fast and Versatile Approach Toward High Quality Mixed Quantum Dot‐Salt Crystals

Liquid–Liquid Diffusion‐Assisted Crystallization: A Fast and Versatile Approach Toward High Quality Mixed Quantum Dot‐Salt Crystals

Tuning the Lattice Parameter of InxZnyP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots

Large-Scale Synthesis of Highly Luminescent InP@ZnS Quantum Dots Using Elemental Phosphorus Precursor

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Tuning the Lattice Parameter of In_xZn_yP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots