Doping-Concentration-Induced Ferromagnetism and

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Article

Doping Concentration Induced Ferromagnetism and Anti-Ferromagnetism in InS:Dy Quantum Dots 2

3

3+

Zhifang Li, Tianye Yang, Xiaojuan Zhao, Qi Zhao, Hai Yu, and Mingzhe Zhang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b03009 • Publication Date (Web): 19 Apr 2017 Downloaded from http://pubs.acs.org on April 23, 2017

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The Journal of Physical Chemistry

Doping Concentration Induced Ferromagnetism and AntiFerromagnetism in In2S3:Dy3+ Quantum Dots Zhifang Li†, Tianye Yang†, Xiaojuan Zhao‡, Qi Zhao†, Hai Yu and Mingzhe Zhang*† †State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People's Republic of China. ‡State Key Lab of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130012, People's Republic of China.

∗ Corresponding author E-mail address: [email protected], Tel: +86-431-85168881; fax: +86-431-85168881.

ACS Paragon Plus Environment

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ABSTRACT: Diluted magnetic semiconductors (DMS) quantum dots have been researched extensively due to their potential applications in next-generation spin-based devices. Herein, the cublic In2S3:Dy3+ DMS quantum dots (3-5 nm) with different doping concentrations were synthesized via a gas-liquid phase chemical deposition method. The effect of Dy3+ content on the photoluminescence and ferromagnetism was investigated. The PL emission spectra exhibit blueshift compared with reported previously due to the increased quantum size confinement and enhanced intensity attributed to the Dy3+ doping. The distinct and stronger room temperature ferromagnetism is observed from VSM measurement. The coexistence of FM and AFM phases and antiferromagnetic interation plays a dominant position after a certain doping concentration value can be further confirmed according to the ZFC-FC curves. As revealed in the magnetic origin study from first-principles calculations, the ferromagnetism obtained arises not only from the Dy atoms but also from the In vacancies. In addition, we also proposed a spontaneous mechanism based on the bound magnetic polaron theory to explain the change of saturation magnetizations along with Dy3+ doping concentration. This work provides experimental and theoretical guidance for designing and synthesizing unique spintronic materials, which can promote development of spintronic applications.


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1. INTRODUCTION Nanoscale magnetism plays an increasingly significant role in new generation magnetic storage devices and microelectronic industries.1-3 Especially some novel materials with Curie temperatures higher (Tc) well in excess of room temperature and high saturation magnetization (Ms) remains a continuous priority.4-6 Diluted magnetic semiconductors (DMSs) quantum dots (QDs)7,8meet aforementioned needs and have attracted considerable attention owing to their remarkable magneto-optical effect and three-dimensional quantum confinement of electrons and holes in recent years.9-11 It opens the prospect of combing information processing and storage functionalities in one material and has potential applications in the emerging field of spin-based electronics or spintronics12,13, such as miniaturization of electronic devices, high density data storage systems, and magnetic fluids.14-16 Nowadays, much effort has been devoted to the exploration of these new DMS nanomaterials to achieve their practical applications, which at the same time provide precise and insightful guidance for designing and synthesizing unique spintronic materials.17-19 Sulfide compounds with spinel-related structure become much more promising as a fascinating host material owing to their massive empty sites, which is particularly in favor of incorporation of guest ions.20,21 Among various chalcogenide semiconductors, β-In2S3 is a typical III–VI group defect spinel structured chalcogenide with a large amount of vacancies. Recently, there are more and more researches focused on the β-In2S3 nanoparticles due to its interesting optical, electrical and magnetic properties.22,23 Doping is a widely used method that involves intentional incorporation of impurities into host materials to generate materials with desirable functions. The rare earth cations, having the totally shielding of the 4f orbital by 5s and 5p orbital, play a crucial role in deciding the electrical and magnetic properties.24,25


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Technologically, the rare earth substituted nanocrystals have both ferromagnetism and semiconductor capabilities, and raises the exciting potential prospects of spintronic applications, where logic and memory operations could in principle be seamlessly integrated on a single device.26 In the current paper, we present a gas-liquid phase chemical deposition method to synthesize the cublic phase In2S3:Dy3+ semiconductor quantum dots of size of about 3-5 nm with different doping concentrations. We have investigated the effect of Dy3+ ions concentration on structural, optical and magnetic properties. Meanwhile, our samples exhibit stronger ferromagnetism than those reported previously. In addition, the theoretical calculation applying to the spin-polarized total and partial density of states was performed by using VASP to further shed light on the origin of the ferromagnetism. 2. EXPERIMENTAL SECTION 2.1. Synthesis of In2S3:Dy3+ quantum dots. All reagents were purchased commercially (analytic grade) and were used without further purification. The reagent-grade water used throughout this work was produced by a Milli-Q Academic ultrapure water purification system. The In2S3 and In2S3:Dy3+ nanoparticles used in this experiment were synthesized by an easily reproducible

gas–liquid

phase

chemical

deposition,

in

which

indium

acetate

(In(COOCH3)3•3H2O(purity 99.99%)) was used as the In precursor, dysprosium acetate hydrate (Dy(COOCH3)3 •4H2O(purity 99.99%)) was used as doping agent, and H2S as sulfur source. In the first synthesis step, dysprosium acetate hydrate and indium acetate were mixed in accordance with Dy3+ molar concentration ratios of 0.03, 0.06, 0.09 and 0.12. Then the surface-active agent mercaptoethanol (HOCH2CH2SH, 60 mmol L-1) was gradually added into the prepared solutions with stirring. The H2S gas was prepared by HCl reacting with Na2S according to the ratio of 2:1.


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The reaction process was consistent with our previous publication.27 The reaction equations are as follow: 2HCl + Na2S → H2S↑+ 2NaCl In3+ + Dy3+ + HOCH2CH2SH + H2S↑→ In2S3:Dy3+↓ The resulting precipitates were centrifuged and washed at 13,000 rpm for 10 min with deionized water and anhydrous alcohol several times. Yellow products were harvested after being repeatedly washed and then dried in a nitrogen atmosphere at room temperature. 2.2. Characterization. The crystal structures of the synthesized samples were characterized by X-ray powder diffraction (XRD, D/ Max-2550, Rigaku, Japan) with Cu Kα (λ = 0.154 nm) radiation at 50 kV and 200 mA in the range of 20–70° (2θ) at a scanning rate of 5° min−1. High resolution transmission electron microscopy (HRTEM) images and selected area electron diffraction (SAED) were obtained on a JEOL JEM-2200FS microscope operated at 200 kV by depositing the samples onto a carbon-coated copper grids film. The dopant concentrations of the samples were investigated by energy dispersive X-ray spectroscopy (EDX) using a Magellan 400, FEI microscope operating at 18 kV. The real doping compositions were a weighted average calculated by two samples for every concentration and one sample tested five times. The X-ray photoelectron spectroscopy (XPS) (ESCALAB MK II) was used to further determine whether the element was doped into the host material and the valence states of elements. Photoluminescence

(PL)

spectra

were

recorded

on

a

FluoroMax-4

fluorescence

spectrophotometer (Horiba Scientific) equipped with a 450 W xenon arc lamp. The magnetic properties were obtained using superconducting quantum interference device (SQUID) with a maximum applied magnetic field of 6T and in the temperature range between 2 to 380 K. In this way, both isothermal magnetization curves as well as Zero Field Cooling/Field Cooling


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(ZFC/FC) measurements were performed and systematically analyzed to obtain various parameters. Magnetisation behaviour such as magnetization hysteresis loops at room temperature were carried out using Vibrating Sample Magnetometer (VSM, Lakeshore 7410 series) with a sensitivity of 10-7 emu. In order to explore the magnetic mechanism in this system, the first-principles calculations were performed by using Vienna Ab-initio Simulation Package (VASP) based upon density functional theory (DFT) and the projector augmented-wave plane-wave (PAW) pseudopotential theory.28 PBE approximation and generalized gradient approximation (GGA and GGA+U) were chosen for the exchange of correlated function. In the calculations, the cut off energy for the plane-waves was chosen to be 320 eV, and a conventional cell with 40 atoms was studied for three models. They were (a) the ideal system with no defect and dopant (In16S24), (b) one In vacancy created by removing one In atom (In15S24), (c) the 6.25% dopant concentration modeled by one In atom replacing one Dy atom (In15Dy1S24). A mesh of 2k×2k×2k points was selected for Brillouin zone integration by the scheme of Monkhorst–Pack.29 The lattice parameter calculated by the GGA function for In2S3 is 10.774 Å, which is very good agreement with the experimental value. 3. RESULTS AND DISCUSSION The microstructure of the as-prepared In2S3:Dy3+ nanoparticles were further investigated by high-resolution TEM (HRTEM) images obtained from the edge of the nanoparticles (Figure 1a). We can observe that the particles can be clearly distinguished and composed of nanocrystals of sizes ranging from 3 to 5 nm. The calculated lattice fringe spacing is 0.268 nm, which is assigned to the (400) plane of In2S3 and consistent with the XRD result. Moreover, the corresponding selected area electron diffraction (SAED) image (Figure 1b) can be indexed to the expected


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cubic crystal lattice of In2S3 (JCPDS No. 84-1385) with characteristic (111), (311), (400), (440) and (533) reflections. It further confirms that the sample is polycrystalline and high crystallinity. To closely investigate at the inside of In2S3:Dy3+ nanoparticles, EDX pattern and elemental mapping images of 1.43 at. % doping content sample shown in Figure 1c. The presence of various well-defined peaks of C, In, S and Dy confirms the formation of high purity In2S3:Dy3+ nanoparticles. The obtained atomic percentages of In, S and Dy are 37.75, 60.82 and 1.43 respectively. Moreover, the ratio of In to S is approximately 1:1.55 smaller than that of the pure In2S3 sample, which implies that Dy dopant is in favor of the In vacancy defects. EDS elemental mapping was performed to detect the elemental distribution. Although the limitation of EDS quantitative analysis, it is found that Dy-elemental mapping across the whole area exhibit uniform dark-blue, which further confirms Dy doping is homogeneously dispersed over the entire region. Figure 1d illustrates that the X-ray diffraction patterns of the In2S3:Dy3+ nanoparticles synthesized with different Dy3+ doping concentrations. The doping contents were measured by EDS testing and statistical calculations. All three patterns are well corresponding to the cubic phase of β-In2S3 structure (JCPDS No. 84-1385), which belongs to Fd-3m space group with a lattice constant of a =10.774 Å. No characteristic peaks were observed for impurities such as Dy, In2O3 or InS, indicating high purity of the obtained samples. The broadening diffraction peaks reveals that the particles are nano sized. By using the Scherrer equation, the particle size of the (440) peak of the XRD was estimated to be 3.782 nm which is in accordance with the TEM results mentioned in Figure 1a. In addition, there is no remarkable shift of all diffraction peaks for different Dy3+ doping concentrations implying that doping cannot change the original crystal


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structure of the host semiconductor. The reason for this phenomenon may be that the low Dy3+ doping content beyond the limit of XRD detection.

Figure 1. (a) HRTEM images and (b) SAED pattern of In2S3:Dy3+ nanoparticles (1.95 at. % content); (c) EDX pattern and elemental mapping images In2S3:Dy3+ nanoparticles (1.43 at. % content), the inset is the corresponding test area; (d) XRD patterns of In2S3:Dy3+ nanoparticles with different doping concentrations.

Figure 2. XPS spectrum of the In2S3:Dy3+ (1.43 at. % content) sample: (a) typical XPS survey spectrum, (b) core level spectrum for In 3d, (c) core level spectrum for S 2p, (d) core level spectrum for Dy 3d.


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XPS measurements of the 1.43 at. % In2S3:Dy3+ sample were performed to analyze the surface chemical composition and the valence states of the various elements presented in it. It can be obviously seen that no other impurities are detected as shown in the survey spectrum Figure 2a, which confirms the high chemical purity of the In2S3:Dy3+ nanoparticles. The In 3d spectrum (Figure 2b) show a doublet due to spin-orbit splitting at 445.6 and 453.1 eV corresponding In 3d5/2 and In 3d3/2, respectively. This indicates that In is mainly present in the In3+ state, which is in agreement with the reported literature values.30 Figure 2c exhibits two characteristic peaks at 161.95 and 163.05 eV are attributable to the core levels of S 2p3/2 and S 2p1/2, respectively, manifesting that the S is in S2- state.31,32 Figure 2d presents the Dy 3d XPS spectrum. One peak is centered at 1337.3 eV, which can be assigned to the binding energy of Dy3+.33 The surface S:In atom ratio is calculated to be 1.56 compared to 1.50 for pristine In2S3 according to XPS corroborating the presence of indium vacancies. The results of XPS, combined with EDS analysis, confirm that the Dy3+ ions have been successfully incorporated and dispersed into the In2S3 main structure.

Figure 3. PL emission spectra of pure and In2S3:Dy3+ nanoparticles with different doping concentration excited at 330 nm.


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Figure 3 displays that the PL spectra of In2S3 and In2S3:Dy3+ nanoparticles with different doping concentration excited at a wavelength of 330 nm in anhydrous alcohol solution. Four strong emissions are observed at 469 nm, 482 nm, 492 nm and 563 nm. The emission peak at about 468 nm is assigned to the excitonic recombination and the lower energy peaks (at 482 nm and 492 nm) can be ascribed to near-impurity/near-defect excitonic luminescence.27 The emission peak at 563 nm derived from 4F9/2 → 6H13/2 transition of Dy3+. Compared with previously reported In2S3 QDs, our as-synthesized In2S3 QDs exhibit blue shift of emission.34 It can be attributed to the increased quantum size confinement of the smaller particle size.35,36 In addition, the In2S3:Dy3+ nanoparticles show a higher PL intensity than that of the In2S3 nanoparticles. We consider that the doping increases the defect density giving rise to radiative transition, which enhances PL intensity.37,38 Thus, we believe that the doping is conductive to visible light emission activity of the samples. As shown in Figure 4a, the magnetization (M) of In2S3:Dy3+ nanoparticles with different doping concentrations is plotted as a function of the magnetic field (H), which are measured by VSM with the applied magnetic field in range of -6K to 6K Oe. The details of hysteresis loops for low fields are shown in Figure 4b. The 0 at. % doped nanoparticles show an almost zero hysteresis loop, indicating that the undoped In2S3 is non-magnetic. The other samples exhibit well-defined hysteresis loops, which are indicative of room-temperature ferromagnetic (RTF) behavior. The saturation magnetizations are determined to be 0.0175, 0.0304, 0.0139, 0.0042 emu/g of samples with Dy3+ doping concentration of 0.77, 1.19, 1.43 and 1.95 at. %, respectively. Remarkably, as the Dy3+ concentration increases, the value of the Ms increases initially and then reaches a maximum value at 1.19 at. %, becomes a decrease afterwards. This


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Figure 4. (a) Magnetization hysteresis loop of In2S3:Dy3+ nanoparticles with different doping concentrations at room temperature. (b) Enlarged view in the low field between -400 and 400 Oe. (c) Isothermal magnetization curves of 1.19 at. % In2S3:Dy3+ nanoparticles at different temperatures, the inset is the enlarged view of almost overlap area for 300 and 380 K.


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behaviour can be explained as spontaneous mechanism of ferromagnetic behaviour in diluted magnetic semiconductors arising from a percolation of bound magnetic polaron (BMP).39,40 The BMP induced by the exchange interation of localized carriers with magnetic impurity electron.41 Two independent competing mechanisms are presented in the process of doping. The short range direct exchange interation of the magnetic impurity is antiferromagnetic, whereas the long range interation between bound magnetic polarons is ferromagnetic.42 At lower doping concentration, the antiferromagnetic can be neglected.26 After doping concentration reaches a certain value, the antiferromagnetic interation assumes a dominant position and reduces the ferromagnetic behavior. Figure 4c displays a systematic study of isothermal magnetization curves measured at 10, 300 and 380 K in a field between -60 and 60 KOe. The saturation magnetization decreases from 1.6412 to 0.3348 emu/g at 60 KOe as temperature increases from 10 to 380K. The two curves at 300 and 380 K tend to be in a state of superposition, indicating that the saturation magnetization is nearly constant above room temperature.

Figure 5. M-T curves for In2S3:Dy3+ samples with 0.77, 1.19 and 1.43 at. % doping concentrations in zero-field cooling (ZFC) and field cooling (FC) modes at a magnetic field of 500 Oe.


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The temperature dependent magnetization zero-field cooling (ZFC) and field cooling (FC) were carried out to further explain the intrinsic magnetic properties. Figure 5 illustrates that ZFC-FC curves of different doping Dy3+ concentration of 0.77, 1.19, and 1.43 at. %. In the ZFC measurements, the samples were cooled down to low temperature without using any external magnetic field and then recorded on warming by application of the field, whereas the FC measurements were performed by previous cooling the samples in same magnetic field. As can be seen, there is no obvious magnetic transition for all samples within the measuring temperature range of 50-400 K. The magnetizations increase gradually with the decrease of the temperature and a rapid increase occurs below 50 K in both ZFC and FC curves, which is similar to paramagnetic behavior. But, the steep rise observed at low temperature and the remanent magnetization at room temperature can be considered as ferromagnetic characteristics. As shown for 0.77 and 1.19 at. % Dy3+-doping nanoparticles, the distinct divergence between corresponding ZFC and FC curves, suggests the existence of room temperature ferromagnetism.43 This behavior is characteristic of all DMS materials and probably related to the defects structure and possible coexistence of FM and AFM phases.14, 44 In addition, the 1.43 at. % doping sample behaves almost identical ZFC and FC curves, indicating the presence of antiferromagnetic properties.45It further verified that antiferromagnetic interation plays a dominant position after a certain doping concentration value.


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Figure 6. Three calculation models: (a) the ideal system with no defect and doping (In16S24); (b) one In vacancy created by removing one In atom (VIn) (In15S24), and the black imaginary circle is the site of the removed In atom; (c) one In atom replaced by one Dy atom (DyIn) (In15Dy1S24).

Figure 7. Spin-polarized total and partial DOS of three models using GGA: (a) the ideal system with no defect and doping (In16S24); (b) the system with one In vacancy defect (VIn) (In15S24); (c) the system with one Dy doping defect (DyIn) (In15Dy1S24). The Fermi level is set at zero energy and indicated by the black vertical dotted lines. Positive values correspond to the spin up and negative values to the spin down. To further shed light on the origin of FM of as-synthesized samples, the first-principles calculations were performed. As shown in Figure 6, three conventional cell models have been built. Figure 6a is corresponding to the ideal system of pure In2S3 (In16S24) with the optimized


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lattice constants (a = 10.774 Å), which agree well with the experimental values. Figures 6b and 6c are corresponding to In15S24 and In15Dy1S24, respectively. In order to investigate the magnetic interactions, the spin-polarized total and partial densities of states using GGA and GGA+U are illustrated in Figure 7 and Fig.S1. For ideal system (as shown in Figure 7a), the number of upspin electrons is equal to the number of down-spin electrons, which indicates that there are no resultant spin polarization phenomenon. Meanwhile, it is found that for both In15S24 and In15Dy1S24 corresponding to Figure 7b and Figure 7c, the total DOS have obviously spin polarization in both conduction band and valence band. In addition, it is clear that the Femi level crosses the spin-up channels and the spin-down channels, indicating magnetic semiconducting properties.46 Hence, the ferromagnetism of the as prepared In2S3: Dy3+ nanoparticles originates not only from the Dy atoms but also from the In vacancies. The calculated total magnetic moments of VIn and DyIn defects are 1.0027 and 1.9825 µB, respectively, which mainly stems from strong hybridization effect between S-3p and In-5p orbitals. Furthermore, from the screening plots, we can clearly observe that the introduced Dy-d orbital contributes the most of the bottom of the conduction band. The Dy doping induces defect states in band gap by hybridizing the Dy-d, S-p and In-p states, shrinking the impurities’ energy level away from the forbidden band in comparison the pure case. The defect formation energies of In15S24 and In15Dy1S24 systems are calculated as -9.195 and −17.155 eV by following formula: E f = Edefect − EIn16 S24 + (

1 EIn S − µ S ) 16 16 24

This indicates that the doping Dy3+ can strongly decrease the defect formation energy and favour producing more In vacancies, which induces the enhancement of the magnetic property of the In2S3 system.


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4. CONCLUSIONS In summary, we have successfully synthesized the high purity undoped and Dy3+-doped indium sulfide semiconductors quantum dots (around 3-5 nm) via an easily reproducible gasliquid phase chemical deposition method. The PL emission spectra exhibit three strong emissions and obvious blue-shift compared with the In2S3 quantum dots (6-10 nm) reported previously. Meanwhile, the Dy3+ doping improves their photoluminescence intensity and visible light emission activity. Furthermore, our as synthesized DMS QDs exhibit room temperature ferromagnetism and the maximum saturation magnetization 0.0304 emu/g is at Dy3+ doping concentration of 1.19 at. %. And it is also further explained and discussed by using BMP theory. The ZFC-FC curves confirm the coexistence of FM and AFM phases and antiferromagnetic interation plays a dominant role after a certain doping concentration value. Subsequently, three conventional cell models have been built to shed light on the origin of magnetic of the sample and the chemical bonding mechanism has been clearly illustrated by spin-polarized total and partial DOS as well. Further analysis indicates that the ferromagnetism originates from the cooperation of Dy3+ ions doping and the In vacancies. In addition, our present work offers a precise and insightful guidance to search and design diluted magnetic semiconductors quantum dots, which provides promoting development of spintronic applications. ACKNOWLEDGMENT This work was funded by the National Science Foundation of China, No. 61674065 and 11474124 and Project 2016061 Supported by Graduate Innovation Fund of Jilin University. Our calculated work was supported by High Performance Computing Center of Jilin University, China. Thanks for anonymous reviewers for their helpful suggestions on the quality improvement of our present helpful suggestions on the quality improvement of our present paper.


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Supporting Information The Supporting Information is available free of charge via the Internet at http://pubs.acs.org Figure S1 shows the spin-polarized total and partial densities of states using GGA+U. This result is consistent with the GGA calculation. REFERENCES (1) Mandal, S. K.; Mandal, A. R.; Banerjee, S., High Ferromagnetic Transition Temperature in PbS and PbS:Mn Nanowires. Acs Appl. Mater. Interfaces 2012, 4, 205-209. (2) Zhou, Y.; Liu, K.; Xiao, H.; Xiang, X.; Nie, J.; Li, S.; Huang, H.; Zu, X., Dehydrogenation: A Simple Route to Modulate Magnetism and Spatial Charge Distribution of Germanane. J. Mater. Chem. C 2015, 3, 3128-3134. (3) Odio, O. F.; Lartundo-Rojas, L.; Santiago-Jacinto, P.; Martínez, R.; Reguera, E., Sorption of Gold by Naked and Thiol-Capped Magnetite Nanoparticles: An XPS Approach. J. Phys. Chem. C 2014, 118, 2776-2791. (4) Dietl, T., A Ten-Year Perspective on Dilute Magnetic Semiconductors and Oxides. Nat. Mater. 2010, 9, 965-974. (5) Felser, C.; Fecher, G. H.; Balke, B., Spintronics: A Challenge for Materials Science and Solid-State Chemistry. Angew. Chem. Int. Ed. 2007, 46, 668-699. (6) Gao, D.; Yang, G.; Li, J.; Zhang, J.; Zhang, J.; Xue, D., Room-Temperature Ferromagnetism of Flowerlike CuO Nanostructures. J. Phys. Chem. C 2010, 114, 18347-18351. (7) Nelson, H. D.; Bradshaw, L. R.; Barrows, C. J.; Vlaskin, V. A.; Gamelin, D. R., Picosecond Dynamics of Excitonic Magnetic Polarons in Colloidal Diffusion-Doped Cd1–XMnxSe Quantum Dots. ACS Nano 2015, 9, 11177-11191.


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(8) Taniguchi, S.; Green, M., The Synthesis of CdTe/ZnS Core/Shell Quantum Dots Using Molecular Single-Source Precursors. J. Mater. Chem. C 2015, 3, 8425-8433. (9) Hu, T.; Zhang, M.; Wang, S.; Shi, Q.; Cui, G.; Sun, S., Cds:Co Diluted Magnetic Semiconductor Nanocrystals: Synthesis and Ferromagnetism Study. CrystEngComm 2011, 13, 5646-5649. (10) Sapra, S.; Sarma, D. D.; Sanvito, S.; Hill, N. A., Influence of Quantum Confinement on the Electronic and Magnetic Properties of (Ga,Mn)As Diluted Magnetic Semiconductor. Nano Lett. 2002, 2, 605-608. (11) Panmand, R. P.; Kulkarni, M. V.; Valant, M.; Gosavi, S. W.; Kale, B. B., Quantum Confinement of Bi2S3 in Glass with Magnetic Behavior. AIP Advances 2013, 3, 022123. (12) Sinova, J.; Zutic, I., New Moves of the Spintronics Tango. Nat. Mater. 2012, 11, 368-371. (13) Wong, P. K. J.; Zhang, W.; Wang, K.; van der Laan, G.; Xu, Y.; van der Wiel, W. G.; de Jong, M. P., Electronic and Magnetic Structure of C60/Fe3O4(001): A Hybrid Interface for Organic Spintronics. J. Mater. Chem. C 2013, 1, 1197-1202. (14) Schwartz, D. A.; Norberg, N. S.; Nguyen, Q. P.; Parker, J. M.; Gamelin, D. R., Magnetic Quantum Dots: Synthesis, Spectroscopy, and Magnetism of Co2+- and Ni2+-Doped Zno Nanocrystals. J. Am. Chem. Soc. 2003, 125, 13205-13218. (15) Schwartz, D. A.; Kittilstved, K. R.; Gamelin, D. R., Above-Room-Temperature Ferromagnetic Ni2+-Doped ZnO Thin Films Prepared from Colloidal Diluted Magnetic Semiconductor Quantum Dots. Appl. Phys. Lett. 2004, 85, 1395-1397. (16) Ohno, H., Making Nonmagnetic Semiconductors Ferromagnetic. Science 1998, 281, 951956.


18

Page 19 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(17) Tian, S.; Li, Y.-Z.; Li, M.-B.; Yuan, J.; Yang, J.; Wu, Z.; Jin, R., Structural Isomerism in Gold Nanoparticles Revealed by X-Ray Crystallography. Nat Commun 2015, 6. (18) Wang, P.; Xiao, B.; Zhao, R.; Ma, Y.; Zhang, M., Structure-Dependent Spin Polarization in Polymorphic CdS:Y Semiconductor Nanocrystals. Acs Appl. Mater. Interfaces 2016, 8, 66566661. (19) Silva, A. S.; Lourenco, S. A.; Dantas, N. O., Mn Concentration-Dependent Tuning of Mn2+ Emission of Zn1-xMnxTe Nanocrystals Grown in a Glass System. Phys. Chem. Chem. Phys. 2016, 18, 6069-6076. (20) Dedryvère, R.; Olivier-Fourcade, J.; Jumas, J. C.; Denis, S.; Lavela, P.; Tirado, J. L., Electrochemical and 119 Sn Mössbauer Study of Sulfospinels as Anode Materials for LithiumIon Batteries. Electrochim. Acta 2000, 46, 127-135. (21) Dedryvère, R.; Olivier-Fourcade, J.; Jumas, J. C.; Denis, S.; Pérez Vicente, C., Lithium Insertion in Copper, Indium, Tin Thiospinels Characterized by 119 Sn Mössbauer Spectroscopy and Rietveld Analysis. Chem. Mater. 2000, 12, 1439-1445. (22) Liu, Y.; Zhang, M.; Gao, Y.; Zhang, R.; Qian, Y., Synthesis and Optical Properties of Cubic In2S3 Hollow Nanospheres. Mater. Chem. Phys. 2007, 101, 362-366. (23) Gorai, S.; Guha, P.; Ganguli, D.; Chaudhuri, S., Chemical Synthesis of β-In2S3 Powder and Its Optical Characterization. Mater. Chem. Phys. 2003, 82, 974-979. (24) Zhang, J.; Li, R.; Liu, L.; Li, L.; Zou, L.; Gan, S.; Ji, G., Self-Assembled 3D Sphere-Like SrMoO4 and SrMoO4:Ln3+ (Ln = Eu, Sm, Tb, Dy) Microarchitectures: Facile Sonochemical Synthesis and Optical Properties. Ultrason. Sonochem. 2014, 21, 1736-1744. (25) Melagiriyappa, E.; Jayanna, H. S., Structural and Magnetic Susceptibility Studies of Samarium Substituted Magnesium–Zinc Ferrites. J. Alloy. Compd. 2009, 482, 147-150.


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 23

(26) Kaminski, A.; Das Sarma, S., Polaron Percolation in Diluted Magnetic Semiconductors. Appl. Phys. Lett. 2002, 88, 247202. (27) Li, Z.; Wang, P.; Yang, T.; Yu, H.; Xiao, B.; Zhang, M., Enhanced Luminescence with Fast Nanosecond Lifetime in In2S3:Tb3+ Nanophosphors. J. Phys. Chem. C 2015, 119, 27688-27694. (28) Kresse, G.; Joubert, D., From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method. Phys. Rev. B 1999, 59, 1758-1775. (29) Monkhorst, H. J.; Pack, J. D., Special Points for Brillouin-Zone Integrations. Phys. Rev. B 1976, 13, 5188-5192. (30) Vahidshad, Y.; Tahir, M. N.; zad, A. I.; Mirkazemi, S. M.; Ghazemzadeh, R.; Tremel, W., Structural and Optical Properties of Fe and Zn Substituted CuInS2 Nanoparticles Synthesized by a One-Pot Facile Method. J. Mater. Chem. C 2015, 3, 889-898. (31) Guo, J.; Zhou, W.-H.; Li, M.; Hou, Z.-L.; Jiao, J.; Zhou, Z.-J.; Wu, S.-X., Synthesis of Bullet-Like Wurtzite CuInS2 Nanocrystals under Atmospheric Conditions. J. Cryst. Growth 2012, 359, 72-76. (32) Yang, X.; Xue, H.; Xu, J.; Huang, X.; Zhang, J.; Tang, Y.-B.; Ng, T.-W.; Kwong, H.-L.; Meng, X.-M.; Lee, C.-S., Synthesis of Porous ZnS:Ag2S Nanosheets by Ion Exchange for Photocatalytic H2 Generation. Acs Appl. Mater. Interfaces 2014, 6, 9078-9084. (33) Tshabalala, M. A.; Dejene, F. B.; Pitale, S. S.; Swart, H. C.; Ntwaeaborwa, O. M., Generation of White-Light from Dy3+ Doped Sr2SiO4 Phosphor. Physica B: Condens. Matter 2014, 439, 126-129. (34) Sumi, R.; Anita, R. W.; Vijayan, C., Visible-Light Driven Photocatalytic Activity of β Indium Sulfide (In2S3) Quantum Dots Embedded in Nafion Matrix. J. Phys. D: Appl. Phys. 2014, 47, 105103.


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Page 21 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(35) Feng, J.; Zhu, H.; Yang, X., A Controllable Growth-Doping Approach to Synthesize Bright White-Light-Emitting Cd:In2S3 Nanocrystals. Nanoscale 2013, 5, 6318-6322. (36) Dabbousi, B. O.; Rodriguez-Viejo, J.; Mikulec, F. V.; Heine, J. R.; Mattoussi, H.; Ober, R.; Jensen, K. F.; Bawendi, M. G., (CdSe)ZnS Core−Shell Quantum Dots: Synthesis and Characterization of a Size Series of Highly Luminescent Nanocrystallites. J. Phys. Chem. B 1997, 101, 9463-9475. (37) Li, H.; Bao, H. Q.; Song, B.; Wang, W. J.; Chen, X. L., Observation of Ferromagnetic Ordering in Ni-Doped Aln Polycrystalline Powders. Solid State Commun. 2008, 148, 406-409. (38) Yao, B.; Wang, P.; Wang, S.; Zhang, M., Ce Doping Influence on the Magnetic Phase Transition in In2S3:Ce Nanoparticles. CrystEngComm 2014, 16, 2584-2588. (39) Kittilstved, K. R.; Liu, W. K.; Gamelin, D. R., Electronic Structure Origins of PolarityDependent High-Tc Ferromagnetism in Oxide-Diluted Magnetic Semiconductors. Nat. Mater. 2006, 5, 291-297. (40) Wang, X.; Xu, J. B.; Ke, N.; Yu, J.; Wang, J.; Li, Q.; Ong, H. C.; Zhang, R., Imperfect Oriented Attachment: Direct Activation of High-Temperature Ferromagnetism in Diluted Magnetic Semiconductor Nanocrystals. Appl. Phys. Lett. 2006, 88, 223108. (41) Dietl, T.; Spałek, J., Effect of Fluctuations of Magnetization on the Bound Magnetic Polaron: Comparison with Experiment. Appl. Phys. Lett. 1982, 48, 355-358. (42) Giribabu, G.; Murali, G.; Amaranatha Reddy, D.; Liu, C.; Vijayalakshmi, R. P., Structural, Optical and Magnetic Properties of Co Doped CdS Nanoparticles. J. Alloy. Compd. 2013, 581, 363-368.


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(43) Zhong, M.; Wang, S.; Li, Y.; Hu, Y.; Zhu, M.; Jin, H.; Li, Y.; Zhang, H.; Zhao, H., Room Temperature Ferromagnetic Cr–Ni Codoped ZnO Diluted Magnetic Semiconductors Synthesized by Hydrothermal Method under High Pulsed Magnetic Field. Ceram. Int. 2015, 41, 451-457. (44) Aljawfi, R. N.; Rahman, F.; Batoo, K. M., Surface Defect Mediated Magnetic Interactions and Ferromagnetism in Cr/Co Co-Doped ZnO Nanoparticles. J. Magn. Magn. Mater. 2013, 332, 130-136. (45) Aljawfi, R. N.; Mollah, S., Properties of Co/Ni Codoped ZnO Based Nanocrystalline DMS. J. Magn. Magn. Mater. 2011, 323, 3126-3132. (46) Yu, W.; Zhu, Z.; Niu, C.-Y.; Li, C.; Cho, J.-H.; Jia, Y., Dilute Magnetic Semiconductor and Half-Metal Behaviors in 3D Transition-Metal Doped Black and Blue Phosphorenes: A FirstPrinciples Study. Nanoscale Res. Lett. 2016, 11, 1-9.


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Doping-Concentration-Induced Ferromagnetism and

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