Gain High-Quality Colloidal Quantum Dots Directly from Natural

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Gain High-Quality Colloidal Quantum Dots Directly from Natural Minerals Wen-Tian Wu, Hui Liu, Chao Dong, Wen-Jing Zheng, LiLi Han, Lan Li, Shi Zhang Qiao, Jing Yang, and Xi-Wen Du Langmuir, Just Accepted Manuscript • DOI: 10.1021/la5044415 • Publication Date (Web): 17 Feb 2015 Downloaded from http://pubs.acs.org on February 18, 2015

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Gain High-Quality Colloidal Quantum Dots Directly from Natural Minerals Wen-Tian Wu§,‡ , Hui Liu§,‡, † , Chao Dong§, Wen-Jing Zheng§, Li-Li Han§, Lan Li⊥, Shi-Zhang Qiao#, Jing Yang*,§, Xi-Wen Du*,§ §

Tianjin Key Laboratory of Composite and Functional Materials, School of Materials Science

and Engineering, Tianjin University, Tianjin 300072, China ⊥

Institute of Material Physics, Key Laboratory of Display Materials and Photoelectric Devices,

Ministry of Education, Tianjin University of Technology, Tianjin 300384, China #

School of Chemical Engineering, The University of Adelaide, Adelaide, SA 5005, Australia.

KEYWORDS. Quantum dots, laser irradiation, green synthesis, LaMer model, photoconductive devices

ABSTRACT. Green and simple synthesis of high-quality colloidal quantum dots (CQDs) is of great importance and highly anticipated yet not fully implemented. Herein, we achieve successfully direct conversion of natural minerals to highly uniform, crystalline lead sulfide CQDs based on laser irradiation in liquid. The trivial fragmentation of mineral particles by the intense nanosecond laser was found to create localized high degree of monomer supersaturation in oleic acid, initiating the “LaMer growth” of uniform CQDs. The photoconductive device made

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of these CQDs exhibits competitive temporal response of photocurrent with those highly sensitive photodetectors based on PbS CQDs reported in the literatures. Our synthetic strategy paves the way to the most environmentally friendly and convenient mass production of highquality uniform CQDs.

Introduction Colloidal quantum dots (CQDs) have predicted considerable attractive applications in quantum information1, photoelectronics2, spintronics3, and biomedine4, due to their unique properties, such as discrete energy levels, tunable band gaps5, multiple exciton generations6 etc. However, the synthesis of uniform CQDs have long been limited to solution-phase chemistry7, often taken to task for environmental problems8. It has been well accepted that the key point in obtaining highly uniform nanocrystals by wet chemistry is to realize a separation of nucleation and growth, which could be virtualized by the LaMer plot in homogeneous nucleation process9. In contrast to the conventional routes, laser fragmentation of bulk materials in liquid is more rapid and cleaner for preparing CQDs which, however, usually suffer from wide size distribution due to simultaneous nucleation and growth10-13. Therefore, it would be very attractive to develop a synthetic strategy towards laser-driven LaMer growth of uniform CQDs which will substantially overcome the bottleneck problems present currently in both wet chemistry and laser synthesis. Our design principle is the following. On one hand, theoretical studies have shown that a carefully selected laser may fragment the target into monomers which eject rapidly into the surrounding liquid14-16. On the other hand, a proper liquid medium with a high affinity will accommodate the ejected species partially, resulting in localized spaces with high supersaturation of monomers, which will trigger the “burst nucleation”, vital for the LaMer growth of uniform


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nanocrystals. As a concrete example, herein we choose a high-energy nanosecond pulsed laser and OA as the laser source and liquid medium, respectively, to achieve the LaMer growth, resultantly, ground natural galena are successively transformed into highly crystalline uniform PbS CQDs with superior optoelectronic properties. Our synthetic strategy manifests the following advantages: cheap and low-toxic starting materials, ultrafast material conversion (on a time scale of nanosecond laser pulse duration), high-quality CQDs, no intermediates and wastes, and easy extension to other material systems such as PbSe CQDs. Therefore, our work paves the way to the most environmentally friendly and convenient mass acquisition of high-quality CQDs with superior optical and optoelectronic properties directly from abundant natural minerals. Experimental Experimental details for sample preparation, characterization, photoconductive devices fabrication, and transient photocurrent measurements are described in the Supporting Information. Results and Discussion After nanosecond laser irradiation (0.64 J/cm2, see the SI), the colorless OA suspension of ground galena with some precipitates at the bottom (Fig. 1a) abruptly turned into transparent brown colloid (Fig. 1b). In contrast, millisecond laser irradiation of the raw material (60 J/cm2, see the SI) resulted into a yellowish suspension with some subsidence (Fig. 1c), while conventional heating (see the SI) gave a dark yellow solution (Fig. 1d).


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Figure 1. Photographs of the OA suspension of ground galena (a), as-obtained colloids after nanosecond (b) and millisecond (c) laser irradiation, and conventional heating (d) of the suspension. The as-purchased millimeter-sized galena grains (Fig. 2a) were ground into powder (Fig. 2b) and suspended in OA to serve as the starting material. After nanosecond laser irradiation of the suspension, uniform PbS CQDs with size of 4.5 ± 0.5 nm and a low size dispersion (11.1%), given by the statistical analysis on 300 nanoparticles in TEM images (Fig. 2c), were acquired. The selected area electron diffraction pattern of the nanoparticles (Fig. 2c, inset) and highresolution TEM (HRTEM) image (Fig. S1) illustrate clearly the high crystallinity of QDs and coincide with those of the cubic rock salt type structure of bulk PbS. The diffraction peaks in the XRD spectrum of the product also match well with that of the raw material (Fig. 2d), besides, distinct peak broadening is observed, indicating a fine particle size of 6.2 nm based on the Sherrer equation, consistent with the TEM result (Fig. 2c). Meanwhile, the PbS CQDs exhibit a prominent absorption shoulder around 1000 nm and a photoluminescence peak at 1100 nm (Fig. 2e), corresponding to the first exciton transition and band-edge emission, respectively, of PbS nanoparticles in the quantum confinement regime17. In contrast, following millisecond laser


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irradiation and conventional heating, the ground galena turned into non-uniform nanoparticles along a great number of large particles (Fig. 3).

Figure 2. (a, b) Photographs of the galena grains before (a) and after (b) grinding. (c) TEM image of the as-prepared PbS QDs. Top inset: the selected area electron diffraction pattern of the QDs. Bottom inset: particle size distribution and corresponding Gaussian fit. (d) XRD patterns of the QDs (blue) and the ground galena (red). a.u. stands for arbitrary units (same as below). (e) Optical absorption spectrum of the QDs dispersed in cyclohexane (blue) and corresponding photoluminescence (PL) spectrum (red). The weak PL hump from 1200 to 1400 nm might be ascribed to the trapped-state emissions.


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Figure 3. TEM images of the product following millisecond laser irradiation (a) and convensional heating (b) of the OA suspension of ground galena. The fairly large size of ground galena (sub to tens of microns) and the consequential fast precipitation make it difficult to investigate the particles size evolution with nanosecond laser irradiation by using the dynamic light scattering (DLS) technique. Therefore, submicron-sized PbS nanocubes (~ 400 nm) (Fig. S2) prepared via a chemical route (see the SI) were also adopted as raw material for laser treatments. Similar to the case of ground galena as starting material, highly crystalline uniform PbS CQDs (4.1 ± 0.5 nm) were obtained after nanosecond laser irradiation of the submicron nanocubes (Fig. 4a and S3a). As revealed by the DLS technique, following 1 min of irradiation, most of the raw nanocubes were converted directly into QDs smaller than 10 nm without intermediate-sized particles (Fig. 4b). As irradiation time increases to 60 min, the peak shifts towards the left a bit, however, we cannot declare here that the average diameter of QDs truly became smaller due to a relatively large measurement error of DLS, especially for small sizes.


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Figure 4. TEM images (a, c, e) and dynamic light scattering results (b, d, f) of the products following different treatments on the raw PbS nanocubes. (a, b) Nanosecond laser irradiation. (c, d) Millisecond laser irradiation. (c, f) Conventional heating. Inset of (a): HRTEM image of one PbS nanoparticle with crystal plane (200). Scale bar is 2 nm. Inset of (c) shows a HRTEM image of one PbSO4 nanoparticle with crystal planes (111) and (121). Scale bar is 5 nm. In comparison with nanosecond laser ablation, 1 h of millisecond pulse laser irradiation of PbS nanocubes led to a mixture of fine nanoparticles and remaining nanocubes with etched surfaces (Fig. 4c). The HRTEM image of a fine nanoparticle (Fig. 4c, inset) exhibits lattice fringes with spacings of 0.380 and 0.300 nm, corresponding to (111) and (121) crystal planes of orthorhombic PbSO4 (ICCD 83-1720), respectively, suggesting oxidization of PbS during millisecond laser irradiation. Moreover, the XRD pattern (Fig. S3b) displays sharp diffraction peaks coinciding with bulk PbS, indicating that the main product is the remaining large


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nanocubes. The DLS measurements also confirm that submicron particles are dominantly present in the final product of millisecond irradiation (Fig. 4d). Similar results were obtained in the case of conventional heating in air. Non-uniform nanoparticles with size of 10-30 nm and submicron particles with etched surfaces coexist in the product (Fig. 4e). Again, no peak broadening was observed in the corresponding XRD pattern (Fig. S3c, confirming that the primary product consists of large PbS particles. It is noteworthy that, some weak diffraction peaks from PbSO4 can be identified in the XRD pattern (Fig. S3c, inset), which suggests that PbS was also partially oxidized during conventional heating. The DLS results (Fig. 4f) again confirm the existence of considerable amount of submicron particles in the final product. In other controlled experiments, octadecene and acetic acid that have low affinity to PbS were adopted as liquid media for nanosecond laser irradiation, and in both cases, polydisperse nanocrystals were obtained (Fig. S4). To understand how uniform CQDs form under nanosecond laser irradiation, first of all, one should clarify what causes the size reduction of initial large PbS particles, i.e. ground galena or submicron nanocubes, upon nanosecond laser irradiation. Possible mechanisms could be heatingmelting-evaporation model18 and trivial fragmentation originated from the breakup of supercritical matter14-16. (Note that, it has been widely accepted that photofragmentation induced by photoelectron ejection is not effective for unfocused nanosecond Nd:YAG lasers18,19.) By performing careful calculations, we find that the temperature of one 400 nm PbS nanocube under laser irradiation in our case is as high as 14854 K, much higher than the boiling point (Tb = 1573 K) (see the SI). As a result, the highly overheated initial PbS particle (Fig. 5, inset i) by a nanosecond pulse (Fig. 5, red dashed line) will expand in an explosive way (Fig. 5, inset ii), leading to breakup of the supercritical fluid and ejection of monomers and clusters (containing


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10~1000 monomers) into the surrounding liquid at a high speed14-16 . Accordingly, we propose that trivial fragmentation should be responsible to the size reduction here.

Figure 5. Formation scheme of uniform PbS QDs under a nanosecond laser pulse (red dashed line), consistent with the LaMer model (black curve). Insets: i, the OA suspension of ground galena; ii, trival fragmentation of raw particles under a nanosecond laser pulse; iii, burst nucleation in local spaces with highly supersaturated monomers or clusters; iv, uniform PbS quantum dots by subsequent growth. Due to the trivial fragmentation of PbS particles and the confinement of OA, very high concentrations of PbS monomers or clusters are generated around the initial PbS particles. Some of them conjugate with OA molecules through the chelating or bridging of carboxyl group with Pb atom20,21, and the others mix merely with solvent, giving rise to local spaces with homogeneous and highly supersaturated monomers or clusters, i.e. localized high degree of supersaturation. The second stage is the precipitation of monomers (and clusters) from the solvent. Since the clusters are very small, they could behave like the atoms and be treated as quasi-monomers. According to the LaMer model (Fig. 5, black curve), if the degree of supersaturation exceeds a ୬୳ critical value ‫ܥ‬୫୧୬ , “burst nucleation” would be initiated (Fig. 5, inset iii), followed by rapid


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reducing of monomer concentration. When the localized degree of supersaturation gets lower ୬୳ , nucleation stops and nucleus starts to grow by collecting the remaining monomers, than ‫ܥ‬୫୧୬

leading to the separation of nucleation and growth. The growth of nanocrystals will cease after the concentration of the PbS monomers approaches the solubility Cs (Fig. 5, inset iv), resulting in uniform nanocrystals with a relatively small average size (4.5 nm) stabilized by the OA ligands (Fig. S5). Under repetitive pulses, more and more initial particles are explosively fragmented and converted into 4.5 nm CQDs. This process is significantly different from traditional laser ablation performed in liquid media with low affinity, which prohibit the dissolution of the ejected species and the LaMer growth, as demonstrated in the control experiments (Fig. S4). On the contrary, for millisecond laser irradiation with a much longer pulse width (τ = 20 ms), the heat losses become so substantial that the laser fluence threshold for evaporating an initial 400 nm PbS nanocube was found to be J* = 25 ~ 2.5×105 J/cm2, most of which is far beyond the heating capability of the millisecond laser used (i.e. 60 J/cm2). Therefore, although the laser fluence of millisecond laser irradiation is about two orders of magnitude larger than that of nanosecond laser irradiation, most of the initial PbS particles would be only partially evaporated by the millisecond laser beam via heating-melting-evaporation, and localized high degree of supersaturation of PbS monomers could be hardly obtained in this case, leading to mostly amorphous PbS nanoparticles under argon protection (Fig. S6a, S6b). To some extent, the millisecond laser plays a role similar to the conventional heating. Due to the long pulse width, the heat transfer from the heated PbS particles to the surrounding liquid via radiation or convection under millisecond laser irradiation is so substantial that the solvent in the vicinity of the heated particles can be heated transiently. Therefore, at atmosphere, PbS nanocubes could be


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etched by the dissolved oxygen with the aid of hot solvent in the cases of both millisecond laser irradiation and conventional heating, based on the following equation22,23, PbS +2O2 →PbSO4, and PbSO4 precipitates as fine nanoparticles (Fig. 4c and 4e). That is why the as-obtained colloidal solutions after millisecond laser irradiation and conventional heating turn into light color (Fig. 1c and 1d). In contrast, since nanosecond laser irradiation does not possess such obvious heat transfer, the particles could be barely oxidized within the cold solvent by the dissolved oxygen under nanosecond laser irradiation and uniform PbS CQDs were finally produced even under ambient condition. Our synthetic strategy towards uniform CQDs through laser-induced localized high degree of supersaturation is applicable to a wide range of material systems, for example, chalcogenides. Uniform PbSe CQDs with an average size of 3.0 nm were successively prepared by performing similar procedures of nanosecond laser irradiation of raw PbSe powder (Fig. S7a). The diffraction peaks in the XRD spectrum match well with those of face-centered cubic PbSe crystals, where the peak broadening confirms the generation of small sized nanoparticles (Fig. S7b). The optoelectronic property of laser-synthesized PbS CQDs were investigated by performing transient photocurrent measurements on the nanocrystals film at room temperature, and also compared to that of CQDs with similar size prepared via hot injection20. As shown in Fig. 6, by fitting the temporal response of photocurrent with multi-exponential functions, it was found that the carrier lifetimes in the photoconductive device made of laser-synthesized PbS CQDs are similar to that in the CQDs prepared by hot injection. Besides, the decay time constants extend


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from milliseconds to seconds, also competitive with those highly sensitive photodetectors based on PbS nanocrystals in the literatures24.

Figure 6. Temporal response of photocurrent in ethanedithiol treated nanocrystals films of PbS QDs prepared by laser irradiation and hot injection methods. The multi-exponential fittings reveal four decay components with time constants of 2 ms, 36ms, 268 ms, and 1700 ms for laser synthesized QDs, and 10 ms, 43 ms, 234 ms, and 891 ms for QDs by hot injection. Outlook We have demonstrated that the nanosecond laser irradiation technique could convert directly natural minerals into high-quality CQDs via localized LaMer growth. The irradiation of each initial PbS particle in oleic acid by each laser pulse will create localized high degree of supersaturation of monomers, which initiates “burst nucleation” and leads to the separation of nucleation and growth in the homogeneous nucleation process. A large scale of highly crystalline uniform PbS CQDs were successively produced by nanosecond laser irradiation of naturally occurring galena, and demonstrated excellent optoelectronic properties. This synthetic route could be extended to other material systems, i.e. PbSe CQDs. Our strategy greatly simplifies the traditional preparation procedures of high-quality CQDs and no reactants are needed. An


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additional investigation on the particle size control under nanosecond laser irradiation will be conducted.

ASSOCIATED CONTENT Supporting Information. Materials, experimental details, HRTEM of PbS QDs, characterization of the PbS nanocubes, XRD patterns of the products after laser irradiation and conventional heating, TEM images of the products by adopting other solvents for nanosecond laser irradiation of ground galena, FITR spectra of as-prepared PbS QDs and QDs following 1% EDT solusion treatment, characterization of PbSe QDs, theoretical calculation on the temperature of one overheated 400 nm PbS nanocube, XRD pattern of PbS QDs following 1% EDT treatment. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]; [email protected] Present Addresses † School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300401, China Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ‡These authors contributed equally.


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ACKNOWLEDGMENT This work was supported by the Natural Science Foundation of China (Nos. 51171127, 51102176, 51271129 and 11272229), Natural Science Foundation of Tianjin City (Nos.11ZCKFGX01300, 11JCYBJC02000, 09JCZDJC22600 and 14JCYBJC17200), Seed Foundation of Tianjin University, and Program for New Century Excellent Talents in University (No. NCET-13-0414). REFERENCES (1) Juska, G.; Dimastrodonato, V.; Mereni, L. O; Gocalinska, A.; Pelucchi, E.; Towards Quantum-Dot Arrays of Entangled Photon Emitters. Nat. Photonics 2013, 7, 527-531. (2) Graetzel, M;, Janssen, R. A. J.; Mitzi, D. B.;

Sargnet, E. H. Materials Interface

Engineering for Solution-Processed Photovoltaics. Nature 2012, 488, 304-312. (3) Beaulac, R.; Schneider, L.; Archer, P. I.; Barcher, G.; Gamelin, D. R. Light-Induced Spontaneous Magnetization in Doped Colloidal Quantum Dots. Science 2009, 325, 973-976. (4) Ye, L.; Yong, K. T.; Liu, L.; Roy, I.; Hu, R.; Zhu, J.; Cai, H.; Law, W. C.; Liu. J.; Wang, K.; Liu, J.; Liu, Y.; Hu, Y.; Zhang, X.; Swihart, M. T.; Prasad, P. N. A Pilot Study in NonHuman Primates Shows No Adverse Response to Intravenous Injection of Quantum Dots. Nat. Nanotechnol. 2012, 7, 453-458. (5) Morrels, I.; Lambert, K.; Smeets D.; De Muynck D.; Nollet, T,; Martins, J. C.; Vanhaecke, F.; Vantomme, A.; Delerue C.; Allan, G.; Hens Z. Size-Dependent Optical Properties of Colloidal PbS Quantum Dots. ACS Nano 2009, 3, 3023-3030.


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(6) Ellingson, R. J.; Beard, M. C.; Johnson, J. C.; Yu, P.; Micic, O. I.; Nozik, A. J.; Shavbav, A.; Efros, A. L. Highly Efficient Multiple Exciton Generation in Colloidal PbSe and PbS Quantum Dots. Nano Lett. 2005, 5, 865-871. (7) Kwon, S. G.; Hyeon, T. Colloidal Chemical Synthesis and Formation Kinetics of Uniformly Sized Nanocrystals of Metals, Oxides, and Chalcogenides. Acc. Chem. Res. 2008, 41, 1696-1709. (8) Anastas, P. T.; Kirchhoff, M. M. Origins, Current Status, and Future Challenges of Green Chemistry. Acc. Chem. Res. 2002, 35, 686-694. (9) Park, J.; Joo, J.; Kwon, S. G.; Jang, Y.; Hyeon, T. Synthesis of Monodisperse Spherical Nanocrystals. Angew. Chem. Int. Ed. 2007, 46, 4630-4660. (10) Pan. S. S.; Yu, S. F.; Zhang, W. F.; Zhu, H.; Lu, W.; Jin, L. M. Low Threshold Amplified Spontaneous Emission from Tin Oxide Quantum Dots: A Instantiation of Dipole Transition Silence Semiconductors. Nanoscale 2013, 5, 11561-11567. (11) Singh, S. C.; Mishra, S. K.; Srivastava, R. K.; Gopal, R. Optical Properties of Selenium Quantum Dots Produced with Laser Irradiation of Water Suspended Se Nanoparticles. J. Phys. Chem. C 2010, 114, 17374-17384. (12) Zeng, H.; Yang, S.; Cai, W. Reshaping Formation and Luminescence Evolution of ZnO Quantum Dots by Laser-Induced Fragmentation in Liquid. J. Phys. Chem. C 2011, 115, 5038– 5043. (13) Zeng, H.; Du, X. W.; Singh S. C.; Kulinich S. A.; Yang S.; He, J.; Cai, W. Nanomaterials via Laser Ablation/Irradiation in Liquid: A Review. Adv. Funct. Mater. 2012, 22, 1333-1353.


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(14) Perez, D.; Béland, L. K.; Deryng, D.; Lewis, L. J.; Meunier, M. Numerical Study of The Thermal Ablation of Wet Solids by Ultrashort Laser Pulses. Phys. Rev. B 2008, 77, 014108. (15) Amendola, V.; Meneghetti, M. What Controls the Composition and the Structure of Nanomaterials Generated by Laser Ablation in Liquid Solution? Phys. Chem. Chem. Phys. 2013, 15, 3027-3046. (16) Lorazo, P.; Lewis, L. J.; Meunier, M. Thermodynamic Pathways to Melting, Ablation, and Solidification in Absorbing Solids Under Pulsed Laser Irradiation. Phys. Rev. B 2006, 73, 134108. (17) Akhtar, J.; Azad Malik, M.; O’Brien, P.; Wijayantha, K. G. U.; Dharmadasa, R.; Hardman, S. J. O.; Graham, D. M.; Spencer, B. F.; Stubbs, S. K.; Flavell, W. R.; Binks, D. J.; Sirotti, F.; El Kazzi, M.; Silly, M. A Green Route to Photoelectrochemically active PbS Nanoparticles. J. Mater. Chem. 2010, 20, 2336-2344. (18) Werner, D.; Hashimoto, S. Improved Working Model for Interpreting the Excitation Wavelength- and Fluence-Dependent Response in Pulsed Laser-Induced Size Reduction of Aqueous Gold Nanoparticles. J. Phys. Chem. C 2011, 115, 5063-5072. (19) Pyatenko, A.; Wang, H. Q.; Koshizaki, N.; Tsuji, T. Mechanism of Pulse Laser Interaction with Colloidal Nanoparticles. Laser Photonics Rev. 2013, 7, 596-604. (20) Hines, M. A.; Scholes, G. D. Colloidal PbS Nanocrystals With Size-Tunable NearInfrared Emission: Observation of Post-Synthesis Self-Narrowing of the Particle Size Distribution. Adv. Mater. 2003, 15, 1844-1849.


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(21) Cass, L. C.; Malicki, M.,; Weiss, E. A. The Chemical Environments of Oleate Species within Samples of Oleate-Coated PbS Quantum Dots. Anal. Chem. 2013, 85, 6974-6979. (22) Lobo, A. M.; Nagel, T.; Borchert, M.; Hickey, H.; Weller, H. Photoelectron Spectroscopic Investigations of Chemical Bonding in Organically Stabilized PbS Nanocrystals. J. Phys. Chem. B 2005, 109, 17422-17428. (23) Akhtar, J.; Malik, M. A.; O'Brien, P.; Wijayantha, K. G. U.; Dharmadasa, R.; Hardman, S. J. O.; Graham, D. M.; Spencer, B. F.; Stubbs, S. K.; Flavell, W. R.; Binks, D. J.; Sirotti, F.; El Kazzi, M.; Silly, M. A Greener Route to Photoelectrochemically Active PbS Nanoparticles. J. Mater. Chem. 2010, 20, 2336-2344. (24) Talapin, D. V.; Lee, J.-S.; Kovalenko, M. V.; Shevchenko, E. V. Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications. Chem. Rev. 2010, 110, 389–458.

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