High-Performance Quantum Dots with Synergistic Doping and Oxide

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Surfaces, Interfaces, and Catalysis; Physical Properties of Nanomaterials and Materials

High-Performance Quantum Dots with Synergistic Doping and Oxide Shell Protection Synthesized by Cation Exchange Conversion of Ternary-Composition Nanoparticles Qiumei Di, Xiyue Zhu, Jia Liu, Xiaobin Zhang, Huishan Shang, Wenxing Chen, Jiajia Liu, Hongpan Rong, Meng Xu, and Jiatao Zhang J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.9b00617 • Publication Date (Web): 29 Apr 2019 Downloaded from http://pubs.acs.org on April 30, 2019

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The Journal of Physical Chemistry Letters

High-Performance Quantum Dots with Synergistic Doping and Oxide Shell Protection Synthesized by Cation Exchange Conversion of Ternary-Composition Nanoparticles Qiumei Di†, Xiyue Zhu†, Jia Liu†, Xiaobin Zhang‡, Huishan Shang†, Wenxing Chen†, Jiajia Liu†, Hongpan Rong†, Meng Xu†, Jiatao Zhang†* †. Beijing Key Laboratory of Construction-Tailorable Advanced Functional Materials and Green Applications, School of Materials Science & Engineering, Beijing Institute of Technology, Beijing 100081, China E-mail: [email protected] ‡. Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan. ABSTRACT Insertion of cation impurities into quantum dots (QDs) as dopant has been proved to be an efficient way to tailor their optical, electronic and magnetic properties. However, the low quantum yield (QY) and poor photostability strongly limit their further applications. In this paper, we report a strategy to coat a thin oxide shell around the heterovalent doped QDs for enhancing their QYs and photostability simultaneously. In the case of Ag+ doped CdS QDs, the controlled cation exchange reaction between Cd2+ and ternary Ag3SbS3 nanoparticles not only realizes the Ag+ doping in CdS QDs, but also generates a thin Sb2O3 shell around the surface of the QDs. Enabled by such, as-prepared CdS:Ag@Sb2O3 QDs exhibited enhanced photostability and high QY of 66.5%. We envision the findings present here can inspire more novel protocols for advancing the practical applications of doped QDs.

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doped QDs suffer from the self-purification effect and poor photostability against oxygen and moisture in the ambient atmosphere, which limits their industrial application.[20] Over the past years, many efforts have been made to improve the stability of QDs. Surface passivation of QDs using a second semiconductor material with a higher band gap has been demonstrated to be a widely applicable approach to improve the photostability and QYs.[2, 20-22] Guyot-Sionnest reported that CdSe@ZnS core shell structures displayed enhanced luminescence with 50% QY.[23] Zhong reported that with the overgrowth of a ZnS shell around the Cu:Zn-In-S core nanostructure, the PLQY increased substantially (from 63% to 85%).[2] Ying and co-workers utilized a reverse micro emulsion method to encapsulate the CdSe QDs within a SiO2 shell which exhibited QY of 20% in water.[24] Jung reported CdO surface coating of CdZnS QDs, resulting in increased PLQY and high photochemical stability.[25] Li group realized a protective layer of Al2O3 on the surface of CdSe/CdS QDs with improved photostability and increased QYs to 54%.[20] However, to our best knowledge, overcoating a thin oxide layer around QDs for improving photostability of dopant luminescence, has rarely been reported. Herein, we report a strategy to synergistically realize the efficient heterovalent doping of Ag+ into CdS QDs and overgrowth of a uniform thin oxide shell around the QDs surface. This is accomplished through a nearly complete cation exchange reaction between an excess amount of Cd2+ precursor and the amorphous Ag3SbS3 nanoparticles with a 18:1 molar ratio in a colloidal dispersion system. By controlling the kinetics of cation exchange reactions between amorphous Ag3SbS3 NPs and Cd2+, the surface Sb3+ doping and lattice Ag+ doping of CdS QDs are achieved concurrently. The atomic surface Sb doping could be in-situ converted into thin Sb2O3 shell, effectively protecting the QDs from photooxidation. With the Sb2O3 shell passivation,



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efficient energy transfer from the conduction band of CdS to the Ag+ dopant level is realized, resulting in obvious enhancement in emission. The as-prepared CdS:Ag@Sb2O3 QDs show good dopant photoluminescence at 687 nm with high color purity, enhanced quantum yield up to 66.5% and improved photo- and thermal-stabilities. Cation exchange can realize heterovalent doping in colloidal QDs by the in-situ conversion between M+ in an amorphous/crystalline M2X matrix (where M represents Ag+ or Cu+ and X represents S2-, Se2-) and Cd2+ in the aqueous solution.[9-10,

26]

Inspired by this, the cation exchange reaction between the ternary amorphous Ag3SbS3 NPs and Cd2+ was carried out in solution at 100 oC. According to Pearson’s hard and soft acids and bases (HSAB) theory,[27] proper ligands and solvents may have fundament influences on a specific cation exchange process.[28-29] In our case, an excess amount of Cd2+ precursor and ligands, such as TBP, OLA and OA were employed to enable a nearly complete cation exchange process. By applying this strategy, monodisperse amorphous Ag3SbS3 NPs (see also in Supporting Information, the X-ray diffraction (XRD) pattern and XPS data in Figure S1) were chose as the starting material. Interestingly, after an efficient cation exchange process, trace amount of Ag+ ions were left over as dopants in the dominant deep position of as-formed CdS QDs, while almost all Sb3+ ions were expelled out, and a controllable amount of Sb3+ ions resided at the surface of CdS QDs as surface dopants bounding to O atom. This may be due to the much smaller ionic radius of Sb3+ (0.74 Å )[30] than that of Cd2+ (0.97 Å )[31] and Ag+ (1.15 Å)[32], resulting in the “self-purification”[11] for the Sb3+ ions. With aging of as-obtained CdS QDs in the open air for more than 7 days, the surface Sb doping can be fully in-situ converted to a Sb2O3 coating shell around the surface of CdS QDs. This strategy is illustrated in ACS Paragon Plus Environment

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Figure 1. The residual OLA on the surface of the QDs may act as an oxidation catalytic agent for the oxidation process of Sb3+ in the open air of colloidal solution.[33] As shown in Figure 2A-B, the as-prepared CdS:Ag@Sb2O3 QDs exhibited good monodispersity and can form large area monolayer 2D and multilayer 3D superlattices by adjusting their colloidal concentrations (see also in Figure S2). This effective bottom-up self-assembly lays the foundation for their further applications in large-area films.[34] Deferent from our previous results of cation exchange-enabled heterovalent doping in binary wurtzite (WZ) II-VI QDs at about 25 ~60 oC, in this work, we realized the heterovalent doping in Zinc blende (ZB) phased CdS QDs through cation exchange between Cd2+ and amorphous ternary Ag3SbS3 NPs at ~100 °C. The phase difference may be attributed to the existence of trace surface ligands of antimony tri (isooctyl thioglycollate) (absorbing on the surface of starting materials, Ag3SbS3 NPs). In accordance with our newly published results, thiols and solvents coordinated cation exchange kinetics could lead to novel semiconductor nanocrystal engineering.[35] Further studies were carried out to demanstrate the influence of the antimony tri (isooctyl thioglycollate) ligands on phase transition and the results are shown in Figure S3. With more tri (isooctyl thioglycollate) ligands (1mL) added, the ZB phase CdS QDs with high crystallinity could be obtained. In contrast, washing the starting materials 5 times before cation exchange gave birth to the WZ phase CdS QDs. The HRTEM image of a pristine doped CdS QD is shown in Figure 2C. Herein, the Ag+ doping-induced CdS lattice strain was characterized by image intensity analysis. As is demonstrated in Figure 2C1-C3, intensity line profiles present lattice distortions in the centre part, which is attributed to the valence difference-induced lattice strain.



While line profiles at the edge part show almost no defect, supporting the dominant deep position of Ag doping in the CdS lattice matrix. The corresponding FFT pattern can be assigned to the (111), (311) and (220) planes of ZB phased CdS.[36] EDS elemental mapping of one doped CdS QD by scanning transmission electron microscopy (STEM) spectroscopy further confirmed the dominant deep position of Ag doping (Figure 2D). The Sb residues were found homogeneously located on the QD matrix. The EDS spectrum shows the presence of Ag and Sb with the concentration of 0.18% and 4.5%, respectively (Figure S4A). The size distribution histogram obtained from Figure 2A are provided in Figure S4B. Raman spectrum in Figure 2E represents the 1LO phononic mode of cubic phase CdS at 305 cm-1. The absence of A1(TO) phonon mode of the hexagonal phase position at 228 cm-1 supports the pure cubic phase of the as-formed CdS QDs.[37-38] The powder XRD pattern (Figure 2F) further verified the pure ZB phase of as-formed CdS QDs (JCPDS 10-0454). After aging the as-formed CdS QDs colloids in the open air for more than 7 days, the surface Sb dopant could be in-situ converted into Sb2O3, as is shown in Figure 2F. HRTEM image in Figure 2G disclosed the core @ shell morphology of the resulting QDs. The lattice plane spacing of 0.279 nm is well matched with the (400) lattice distance of cubic Sb2O3, in consistent with the XRD analysis in Figure 2F. This result could further confirm that the Sb2O3 shell is coated around the surface of CdS QDs uniformly. FTIR spectra in Figure 2H further supported the formation of a Sb2O3 shell. The characteristic absorption band at 701cm-1 was very close to the IR-active mode of Sb2O3 at 697cm-1.[39] To further investigate on the Ag and Sb dopants in as-prepared CdS QDs by this cation exchange strategy, a combined analysis using X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and XPS


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characterizations was carried out over pristine and aged CdS QDs. As can be seen in Figure 3A, the similar characteristic feature of Ag K-edge of doped CdS QDs and Ag2S NPs indicates that the Ag impurity in as prepared doped CdS QDs is Ag+.[17, 35]. Figure 3B shows the EXAFS Fourier transforms spectra, the peak at R

2 Å is

attributed to Ag-S bonds, further corroborating that the Ag dopant is not existed as metallic Ag. In addition, the slight shift to lower R region of the Ag-S peak indicates the shrink of Ag-S bond length in as-prepared doped CdS QDs, supporting the absence of Ag2S phase residue in as-prepared QDs. The Ag 3d XPS spectrum (Figure 3C) shows two peaks at 373.9 and 367.9 eV for the d3/2 and d5/2 lines, respectively, which indicates that Ag only presents the chemical state of Ag+.[40] The k-edge XANES spectra in Figure 3D of pristine and aged CdS QDs show the existence and chemical state of Sb. The obvious shift to higher energy compared to the Sb2S3 standard reference indicated that Sb is not bonded to S. From the EXAFS spectra in Figure 3E, the peak at R

1.5 Å is consistent with the reported parameter of Sb-O

bonds[41], while the peak at R

2 Å is assigned to the Sb-S bonds. The Sb element

preferably existed in the oxide phase

[42]

both in the pristine and aged CdS QDs,

suggesting that all Sb atoms were expelled out and Sb did not structurally incorporate into the CdS matrix (absence of Sb-S coordination) after a nearly complete cation exchange process. Instead, it aggregated/attached around the surface of QDs as surface dopants, leading to the coating of CdS QDs with a layer of Sb-containing species that are inclined to oxidation. Then with aging in the open air for 7 days, the active Sb-O bonding residues could be converted into crystalline oxide shell easily. Figure 3F shows the XPS spectra of the Sb residue in QDs. The peaks at 540 eV and 530.5 eV are ascribed to Sb 3d3/2 and Sb 3d5/2 of Sb2O3, respectively.[43] The O (1s) signal could be Gaussian divided into two peaks at 531.1eV and 532.3eV,



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respectively. The major peak at 531.1 eV is assigned to oxygen in the Sb2O3 lattice and the minor peak (532.3 eV) is assigned to absorbed oxygen species on the surface.[44] Figure 3G-H show the XANES and EXAFS spectra of the ZB CdS standard reference and the as-prepared CdS QDs. The Cd K-edge XANES spectra show negligible variation under Ag doping and Sb2O3 coating (Figure 3G), signifying that the CdS matrix is virtually the same in both undoped and doped samples. From the Fourier transforms in Figure 3H, the feature peak at 2.1 Å corresponded to the Cd-S bond which in all samples is almost the same in intensity and position, indicating the dominant deep position doping of Ag+ and surface coating of Sb2O3 shell. The XPS spectrum (Figure 3I) of Cd 3d shows two peaks at 405.1 eV and 411.9 eV, corresponding to Cd 3d5/2 and Cd 3d3/2 transitions respectively, which are well consistent with the reported data of CdS QDs. [17] II-VI QDs can exhibit strong quantum confinement when the radius of QDs is smaller

than

Bohr

radius,[1,3,11]

consequently,

a

strong

exciton-absorption-(1S(e)/1S3/2(h)) is expected in their absorption spectra (Figure 4A). Transient absorption (TA) spectroscopy is applied to probe the relaxation process (Figure 4B). The CdS:Ag@Sb2O3 QDs demonstrated one main areas of bleaching at 465 nm. Compared with the absorption spectrum of as prepared doped CdS QDs (Figure 4A), the observed intervals of bleaching could be ascribed to the 1S(e)-1S3/2(h) transitions in the CdS QDs.[45-46] PLE and PL measurements were carried out to testify the optical properties of as-prepared CdS:Ag@Sb2O3 QDs (Figure 4A). The PL spectrum of CdS:Ag@Sb2O3 QDs is dominated by a broadband emission at ~ 687 nm, Stokes-shifted by 0.86 eV from the 1S absorption peak at 465 nm. Compared with the Ag+ doped CdS QDs (Figure S5), the absence of the band-edge emission (BE-PL) further indicated the efficient energy transfer from the conduction band of the CdS


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QDs to the Ag+ dopant level.[18] Additionally, the red shift of Ag+-PL in the CdS:Ag@Sb2O3 could be ascribed to the larger radius (average size of 5.28 nm) of QDs than that of CdS:Ag QDs in our previous work (average size of 4 nm). This could be attributed to the quantum confinement effect, which is similar with the Peng’ work[47] showing that the doped Cu-PL is red shifted when increasing the sizes of InP: Cu NPs. The PLE spectrum of as prepared QDs exhibited a broad band from 300 to 500 nm, indicating that Ag+-PL at 687nm can be easily excited by the light ranging from UV to the cyan area, laying foundation for its application in lighting at W-LED. By tuning the excitation wavelength from 400 nm (3.0 eV, above the CdS band gap) to 560 nm (2.2 eV, below the CdS band edge of 2.4 eV), Ag+-PL could still be observed (Figure 4C). This may be due to the direct excitation from ground state to Ag+ state, or direct optical excitation from the d electrons of Ag+ to the CB of CdS QDs. Figure 4D presents the CIE chromaticity coordinate of as-prepared CdS:Ag@Sb2O3 QDs with the x and y values of (0.660, 0.335), demonstrating high red color purity. The as-prepared CdS:Ag@Sb2O3 QDs exhibited an efficient Ag+ dopant emission with high QY of 66.5%, which is higher than some previous results.[17] The dopant luminescence of CdS:Ag@Sb2O3 QDs could be stable in the ambient air for more than one and half year. This high quality and stable dopant luminescence is mainly ascribed to the protection of thin Sb2O3 shell coating on the surface of QDs. In addition, the band gap of the shell material Sb2O3 (3.3 eV)[48] is larger than that of the CdS core and the carriers are confined in the core, resulting into the type-I core@shell QDs.[21] To investigate the exciton recombination dynamics, we studied the PL dynamics at fixed wavelength (687 nm), as shown in Figure 4E. The PL decay for CdS:Ag@Sb2O3 QDs can be fitted by a biexponential function (equation 1),



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giving a fast component @V1) of 1.32 W with an amplitude (A1) of 66.6% and a slow component @V2) of 4.37 W with an amplitude (A2) of 33.4% (Table S1). ( )=

1exp

( )+ 1

2exp(

2

)

(1)

In terms of the previous studies of surface-related luminescence in CdSe QDs,[49-50] the fast component @V1) could be assigned to the recombination of intrinsic excitons, while the slow component @V2) may be due to the exciton recombination through surface trap states. Compared with those (0.2 W with A1 of 78% and 1.3 W with A2 of 22%) of CdS:Ag QDs in our previous work[17], the longer lifetime and increasing of amplitude of A2 indicated that the thin Sb2O3 coating layer greatly suppressed the nonradiative recombination. Based on the above characterizations, the schematic illustrating the energy transfer process was summarized in Figure 4F. Based on the passivation effect of the Sb2O3 (bandgap of 3.3eV) shell around the surface of CdS:Ag QDs, this novel type-I core-shell structure ensures the confinement of excitons in CdS QDs, resulting in efficient energy transfer from the conduction band to the Ag+ dopant level and thus accounting for the efficient dopant-related emission. In order to quantify the role of Sb2O3 coating on the emission of Ag+ doped CdS QDs, low temperature PL at 78 K (liquid nitrogen) and temperature-dependent PL studies ranging from 25 to 200 oC were performed. The PL spectra and PL decay curves of as-prepared CdS:Ag@Sb2O3 QDs at 78 K and 298 K are shown in Figure S6. It can be seen that the optical performance is improved when decreasing the temperature from 298 K to 78 K. As a quantitative analysis, the integrated emission intensity and the peak (X = 687 nm) intensity at 78 K increased 660% and 680% compared with the intensity at 298 K. This is due to the confinement of phonon


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vibration at low temperatures, which can reduce the energy loss and obtain efficient photoexcited electron/hole separation. The corresponding decay lifetime is shown in Table S1. As the temperature increased from 25 to 200 oC, thermal quenching (TG) occurred for both CdS: Ag@Sb2O3 and CdS: Ag+ samples (circles in Figure 5A and B). This is because the nonradiative decay processes became dominant at high temperatures. It is worth noticing that with the thin Sb2O3 layer coating on the QDs surface, the thermal stability of Ag+-PL was increased (Figure 5C). As a comparison, the integrated emission intensity of CdS:Ag@Sb2O3 QDs at 100 oC drops to 45% of the initial integrated intensity at RT and the integrated emission intensity of CdS:Ag QDs is 32% of that at RT. Normalized PL spectra of CdS:Ag and CdS:Ag@Sb2O3 at 25, 150 and 200 oC are shown in Figure 5D and E. At most cases, the PL peak was red-shifted with increasing temperatures, which could be explained by the Varshini equation.[51-52] aT2

(2)

E(T) = E0 - T + b

where E(T) is the energy difference between excited states and ground states at a temperature T, E0 is the energy difference at 0 K, a and b are fitting parameters.[51] In this case of Ag+:CdS@Sb2O3 QDs, at a higher temperature, the bond lengths of Ag-S increased,

[51]

resulting in the decreased crystal field of the CdS host and the split of

degenerate excited state of Ag+. Therefore, it would result in the red shift of PL peak at high temperatures.[52] Upon heating the as prepared QDs in a temperature ranging from 25 to 200 oC, CdS:Ag@Sb2O3 displayed a red shift about 13 nm. As for the CdS:Ag QDs, a noticeable blue shift about 20 nm was shown from 25 to 200 oC (Figure 5F), which could not be described by equation 2. The blue shift may be explained by thermally activated phonon assisted excitation from a lower excited state



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to a higher excited state of Ag+.[51] Consequently, the stimulated radiative transition from a higher Ag+ excited state to the ground state caused the blue-shift of CdS:Ag QDs. To further understand the thermal quenching phenomena, the activation energy ( E) of CdS:Ag and CdS:Ag@Sb2O3 QDs were calculated using the Arrhenius equation:[51, 53]

IT =

I0 1 + cexp( -

(3) kT

)

where I0 and IT are the integrated PL intensity at RT and a given temperature, c is a constant, and k is the Boltzmann constant (8.62 × 10 -5 eV). The activation energy ( E) shows the energy gap between the lowest Ag+ excited state and the ground state, which is related to the thermally active energy transfer processes.[51] According to equation 3, E can be calculated from a plotting of ln[(I0/It)-1] versus 1000/T, where the slope equals - E/k. As shown in Figure 5G and H, [

for CdS:Ag QDs was

found to be 0.52 eV. While in the CdS:Ag@Sb2O3 QDs sample, a relative higher E was found to be 0.54 eV. This indicated that the Sb2O3 shell material with a wide band gap (3.3 eV) had a positive impact on improving the thermal stability of CdS:Ag QDs. This is similar with the case of Mn doped core-shell QDs, in which the thermally active escape of carriers can be efficiently eliminated by the high activation energies, leading to enhanced optical performance at high temperatures.[54] The thermal quenching phenomena in our as-prepared doped QDs could be described by the configurational coordinate diagram in Figure 5I. At high temperatures, the electron-phonon coupling is enhanced,[55-56] leading to thermal activation and subsequent release of excited electrons through the intersection of the


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Ag+ excited state and valence band of CdS. As a result, nonradiative decay processes become dominant at high temperatures, as proved by the thermal quenching behaviors of as prepared doped CdS QDs. High photostability of doped QDs is critical for optoelectronic applications, such as LEDs, lasers and LSC. The photostability tests of Ag+ doped CdS QDs with and without Sb2O3 coating were performed by irradiating the samples under UV light with wavelength of 365 nm. Figure 6 A and B illustrated that the photostability of CdS:Ag QDs is improved with Sb2O3 coating on the surface of QDs. The corresponding TEM images of CdS:Ag and CdS:Ag@Sb2O3 QDs after irradiation for 12 hours are shown in Figure S7. After continuous irradiation for 30 h, the integrated PL intensity of CdS:Ag@Sb2O3 QDs was maintained 85%, as a comparison, the PL intensity of the CdS: Ag QDs without oxide shell protection continuously decreased to approximately 57% (Figure 6C). The relative instability can be ascribed to the photoinduced degradation of the CdS:Ag QDs. The blue shift of the emission spectra was observed for both samples after 30 hours irradiation, which can be ascribed to the incompletely crystallized structure after light irradiation.[57] Surface oxidation by air has been proved to be dominantly responsible for the photo-degradation of QDs upon irradiation.[20] Figure 6D and E show XPS spectra of CdS: Ag QDs and CdS: Ag@Sb2O3 QDs before and after UV irradiation. The peaks at 161.3 and 162.5 eV are assigned to S 2p transitions in the Cd-S bond. After UV irradiation for 12 hours, another peak at higher energy between 168~172 eV associated with the SO42- group was observed for the CdS:Ag QDs (Figure 6D), suggesting the oxidation of sulfur,[58] as a comparison, the S 2p XPS spectrum of as-prepared CdS:Ag@Sb2O3 QDs (Figure 6E) was almost unchanged. These results indicated that the coating of a Sb2O3 layer has a positive impact on improving the ACS Paragon Plus Environment


photostability of Ag+ doped CdS QDs. According to the Sb 3d and O 1s XPS spectra in Figure 6F, the as-prepared CdS:Ag@Sb2O3 QDs showed higher O atom absorption after light irradiation, and this can preserve higher emission intensity by protecting the CdS core from photo-degradation. Furthermore, PEC measurements and UV photoelectron spectroscopy (UPS) characterizations were performed to investigate the influence of Sb2O3 coating on the electrochemical properties of CdS:Ag QDs. As shown in Figure S8, as-prepared QDs preserved the n-type conductivity, which further indicated that the Sb2O3 coating layer can keep the internal electronic structure of original CdS:Ag QDs and hinder surface defects, contributing to the enhanced optical properties of CdS:Ag QDs. In summary, a new synergistic strategy was developed to form thin Sb2O3 shell coating around the Ag+ doped II-VI QDs. Enabled by the passivation of Sb2O3 shell around the surface of CdS:Ag QDs, efficient energy transfer from the host to the Ag+ dopant level was achieved, which lead to more efficient dopant luminescence with higher QY of 66.5% and higher photostability. These advantages can facilitate their application in high-efficiency QD optical devices, such as lighting in the W-LEDs. This new kind of multiple cation exchange reaction beyond binary cation exchange may enable more flexible control of semiconductor nanocrystals with regard to their composition and surface engineering. Supporting Information Figure S1-S8, Table S1. This material is available free of charge via the Internet at http://pubs.acs.org AUTHOR INFORMATION Corresponding Author


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*E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grant No. 51872030, 51631001, 51702016, 51501010, 21643003), Fundamental Research Funds for the Central Universities. We acknowledge critical and quantity of testing work supported by Beijing Zhongkebaice Technology Service Co., Ltd. REFERENCES (1) Dai, X. L.; Zhang, Z. X.; Jin, Y. Z.; Niu. Y.; Cao. H. J.; Liang. X. Y.; Chen, L. W.; Wang. J. P.; Peng. X. G. Solution-Processed, High-Performance Light-Emitting Diodes Based on Quantum Dots. Nature 2014, 515, 96-99. (2) Zhang, W. J.; Lou, Q.; Ji, W. Y.; Zhao, J. L.; Zhong, X. H. Color-Tunable Highly Bright Photoluminescence of Cadmium-Free Cu-doped Zn-In-S Nanocrystals and Electroluminescence. Chem. Mater. 2014, 26, 1204-1212. (3) Klimov, V. I.; Mikhailovsky, A. A.; Xu, S.; Malko, A.; Hollingsworth, J. A.; Leatherdale, C. A. ; Eisler, H. -J.; Bawendi, M. G. Optical Gain and Stimulated Emission in Nanocrystal Quantum Dots. Science 2000, 290, 314-317. (4) Freeman, R.; Finder, T.; Bahshi, L.; Gill, R.; Willner, I. Functionalized CdSe/ZnS QDs for the Detection of Nitroaromatic or RDX Explosives. Adv. Mater. 2012, 24, 6416-6421. (5) Wei, Q. L.; Zhao, Y. H.; Di, Q. M.; Liu, J. J.; Xu, M.; Liu, J.; Zhang, J. T. Good Dispersion of Large-Stokes-Shift Heterovalent-Doped CdX Quantum Dots into Bulk



PMMA Matrix and Their Optical Properties Characterization. J. Phys. Chem. C 2017, 121, 6152-6159. (6) Li, H. B.; Wu, K. F.; Lim, J.; Song, H. J.; Klimov, V. I. Doctor-Blade Deposition of Quantum Dots onto Standard Window Glass for Low-Loss Large-Area Luminescent Solar Concentrators. Nat. Energy 2016, 1, 16157. (7) Meinardi, F.; Colombo, A.; Velizhanin, K. A.; Simonutti, R.; Lorenzon, M.; Beverina, L.; Viswanatha, R.; Klimov, V. I.; Brovelli, S. Large-Area Luminescent Solar Concentrators Based on ‘Stokes-Shift-Engineered’ Nanocrystals in a Mass-Polymerized PMMA Matrix. Nat. Photonics 2014, 8, 392-399. (8) Guria, A. K.; Dutta, S. K.; Adhikari, S. D.; Pradhan, N. Doping Mn2+ in Lead Halide Perovskite Nanocrystals: Successes and Challenges. ACS Energy Lett. 2017, 2, 1014-1021. (9) Liu, J.; Zhao, Y. H.; Liu, J. L.; Wang, S. G.; Cheng, Y.; Ji, M. W.; Zhou, Y. M.; Xu, M.; Hao, W. C.; Zhang, J. T. From Cu2S Nanocrystals to Cu Doped CdS Nanocrystals through Cation Exchange: Controlled Synthesis, Optical Properties and Their p-type Conductivity Research. Sci. China Mater. 2015, 58, 693-703. (10) Zhang, J. T.; Di, Q. M.; Liu, J.; Bai, B.; Liu, J.; Xu, M.; Liu, J. J. Heterovalent Doping in Colloidal Semiconductor Nanocrystals: Cation Exchange Enabled New Accesses to Tuning Dopant Luminescence and Electronic Impurities. J. Phys. Chem. Lett. 2017, 8, 4943-4953. (11) Norris, D. J.; Efros, A. L.; Erwin, S. C. Doped Nanocrystals. Science 2008, 319, 1776-1779. (12) Di, Q. M.; Zheng, J. J.; Bai, B.; Liu, J. J. ; Xu, M.; Zhang, J. T. Research Progress in Solution-Based Synthesis of Doped Collidal Semiconductor Nanocrystals. Chin. J. Rare Met. 2017, 41, 475-486.


Page 16 of 28

Page 17 of 28 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


(13) Whitham, P. J.; Knowles, K. E.; Reid, P. J.; Gamelin, D. R. Photoluminescence Blinking and Reversible Electron Trapping in Copper-Doped CdSe Nanocrystals. Nano Lett. 2015, 15, 4045-4051. (14) Jana, S.; Manna, G.; Srivastava, B. B.; Pradhan, N. Tuning the Emission Colors of Semiconductor Nanocrystals beyond Their Bandgap Tunability: All in the Dope. Small 2013, 9, 3753-3758. (15) Brovelli, S.; Galland, C.; Viswanatha, R.; Klimov, V. I. Tuning Radiative Recombination in Cu-Doped Nanocrystals via Electrochemical Control of Surface Trapping. Nano Lett. 2012, 12, 4372-4379. (16) Sahu, A.; Kang, M. S.; Kompch, A.; Notthoff, C.; Wills, A. W.; Deng, D.; Winterer, M.; Frisbie, C. D.; Norris, D. J. Electronic Impurity Doping in CdSe Nanocrystals. Nano Lett. 2012, 12, 2587-2594. (17) Liu, J.; Zhao, Q.; Liu, J. L.; Wu, Y. S.; Cheng, Y.; Ji, M. W.; Qian, H. M.; Hao, W. C.; Zhang, L. J.; Wei, X. J., Wang, S. G., Zhang, J. T. Heterovalent Doping Enabled Efficient Dopant Luminescence and Controllable Electronic Impurity Via a New Strategy of Preparing II-VI Nanocrystals. Adv. Mater. 2015, 27, 2753-2761. (18) Pinchetti, V.; Di, Q. M.; Lorenzon, M.; Camellini, A.; Fasoli, M.; Zavelani-Rossi, M.; Meinardi, F.; Zhang, J. T.; Crooker, S. A.; Brovelli, S. Excitonic Pathway to Photoinduced Magnetism in Colloidal Nanocrystals with Nonmagnetic Dopants. Nat. Nanotechnol. 2018, 13, 145-151. (19) Erwin, S. C.; Zu, L.; Haftel, M. I.; Efros, A. L.; Kennedy, T. A.; Norris, D. J. Doping Semiconductor Nanocrystals. Nature 2005, 436, 91-94. (20) Li. Z. C.; Yao, W.; Kong. L.; Zhao, Y. X.;

Li. L. General Method for the

Synthesis of Ultrastable Core/Shell Quantum Dots by Aluminum Doping. J. Am. Chem. Soc. 2015, 137, 12430-12433.



Page 18 of 28

(21) Reiss, P.; Protière, M.; Li, L. Core/Shell Semiconductor Nanocrystals. Small 2010, 5, 154-168. (22) Zhou, J. H.; Pu, C. P.; Jiao, T. Y.; Hou, X. Q.; Peng, X. G. A Two-Step Synthetic Strategy

toward

Monodisperse

Colloidal

CdSe

and

CdSe/CdS

Core/Shell

Nanocrystals. J. Am. Chem. Soc. 2016, 138, 6475-6483. (23) Hines, M. A.; Guyot-Sionnest, P. Synthesis and Characterization of Strongly Luminescing ZnS-Capped CdSe Nanocrystals. J. Phys. Chem. 1996, 100, 468-471. (24) Selvan, S. T.; Tan, T. T.; Ying, J. Y. Robust, Non-Cytotoxic, Silica-Coated CdSe Quantum Dots with Efficient Photoluminescence. Adv. Mater. 2005, 17, 1620-1625. (25) Cho, J.; Jung, Y. K.; Lee, J.-K.; Jung, H.-S. Surface Coating of Gradient Alloy Quantum Dots with Oxide Layer in White-Light-Emitting Diodes for Display Backlights. Langmuir 2017, 33, 13040-13050. (26) Gui, J.; Ji, M. W.; Liu, J. J.; Xu, M.; Zhang, J. T.; Zhu, H. S. Phosphine-Initiated Cation Exchange for Precisely Tailoring Composition and Properties of Semiconductor Nanostructures: Old Concept, New Applications. Angew. Chem. 2015, 54, 3754-3758. (27) Pearson, R. G. Chemical Hardness and Bond Dissociation Energies. J. Am. Chem. Soc. 1988, 110, 7684-7690. (28) Trizio, L. D.; Manna, L. Forging Colloidal Nanostructures via Cation Exchange Reactions. Chem. Rev. 2016, 116, 10852-10887 (29) Lee, D.; Kim, W. D.; Lee, S.; Bae, W. K.; Lee, S.; Lee, D. C. Direct Cd-to-Pb Exchange of CdSe Nanorods into PbSe/CdSe Axial Heterojunction Nanorods. Chem. Mater. 2015, 27, 5295-5304.


Page 19 of 28 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


(30) Blasse, G. Luminescence of Calcium Halophosphate-Sb3+, Mn2+ at Low Temperatures. Chem. Phys. Lett. 1984, 104, 160-162. (31) Sellaoui, L.; Soetaredjo, F. E.; Ismadji, S.; Bonilla-Petriciolet, A.; Belver, C.; Bedia, J.; Lamine, A. B.; Erto, A. Insights on the Statistical Physics Modeling of the Adsorption of Cd2+ and Pb2+ Ions on Bentonite-Chitosan Composite in Single and Binary Systems. Chem. Eng. J. 2018, 354, 569-576. (32) Wu, Y. F.; Xu, L. X.; Shen, Y. N.; Wang, Y.; Zou, L.; Wang, Q. C.; Jiang, X. Q.; Liu, J. S.; Tian, H. The Smallest Cucurbituril Analogue with High Affinity for Ag+. Chem. Commun. 2017, 53, 4070-4072. (33) Liu, L. G.; Zhong, H. Z.; Bai, Z. L.; Zhang, T.; Fu, W. P.; Shi, L. J.; Xie, H. Y.; Deng, L. G.; Zou, B. S. Controllable Transformation from Rhombohedral Cu1.8S Nanocrystals to Hexagonal CuS Clusters: Phase-and Composition-Dependent Plasmonic Properties. Chem. Mater. 2013, 25, 4828-4834. (34) Huang, L.; Zheng, J. J.; Huang, L. L.; Liu, J.; Ji, M. W.; Yao, Y.; Xu, M.; Liu, J. J.; Zhang, J. T.; Li, Y. D. Controlled Synthesis and Flexible Self-Assembly of Monodisperse Au@Semiconductor Core/Shell Hetero-Nanocrystals into Diverse Superstructures. Chem. Mater. 2017, 29, 2355-2363. (35) Bai, B.; Xu. M.; Li. N.; Chen, W. X.; Liu, J. J.; Liu, J.; Rong, H. P.; Fenske, D.; Zhang, J. T. Semiconductor Nanocrystal Engineering by Applying Thiol- and Solvent- Coordinated Cation Exchange Kinetics. Angew. Chem. Int. Ed. 2019, 58, 4852-4857. (36) Cao, Y. C.; Wang, J. H. One-Pot Synthesis of High-Quality Zinc-Blende CdS Nanocrystals. J. Am. Chem. Soc. 2004, 126 , 14336-14337. (37)

Zelaya-Angel,

O.;

Castillo-Alvarado,

F.

L.;

Avendaño-López,

J.;

Escamilla-Esquivel, A.; Contreras-Puente, G.; Lozada-Morales, R.; Torres-Delgado,



G. Raman Studies in CdS Thin Films in the Evolution from Cubic to Hexagonal Phase. Solid State Commun. 1997, 104 , 161-166. (38) Rossetti, R.; Nakahara, S.; Brus, L. E. Quantum Size Effects in the Redox Potentials, Resonance Raman Spectra, and Electronic Spectra of CdS Crystallites in Aqueous Solution. J. Chem. Phys. 1983, 79 , 1086-1088. (39) Song, L.; Zhang, S.; Wei, Q. Perfect, Sectorial, Branched Sb2O3 Microstructures Consisting of Prolate Microtubes: Controllable Seeded Growth Synthesis and Optical Properties. Crystal Growth & Design 2012, 12, 764-770. (40) Feng, J. W.; Liu, J.; Cheng, X. Y.; Liu, J. J.; Xu, M.; Zhang, J. T. Hydrothermal Cation Exchange Enabled Gradual Evolution of Au@ ZnS-AgAuS Yolk–Shell Nanocrystals and Their Visible Light Photocatalytic Applications. Adv. Sci. 2018, 5, 1700376. (41) Rockenberger, J.; Zum Felde, U.; Tischer, M.; Tröger, L.; Haase, M.; Weller, H. Near Edge X-Ray Absorption Fine Structure Measurements (XANES) and Extended X-Ray Absorption Fine Structure Measurements (EXAFS) of the Valence State and Coordination of Antimony in Doped Nanocrystalline SnO2. J. Chem. Phys. 2000, 112, 4296-4304. (42) Stavrinadis, A.; Pelli Cresi, J. S.; d’Acapito, F.; Magén, C.; Boscherini, F.; Konstantatos, G. Aliovalent Doping in Colloidal Quantum Dots and Its Manifestation on Their Optical Properties: Surface Attachment versus Structural Incorporation. Chem. Mater. 2016, 28, 5384-5393. (43) Tang, R. F.; Wang, X. M.; Jiang, C. H.; Li, S.; Liu, W. F.; Ju, H. X.; Yang, S. F.; Zhu, C. F.; Chen, T. n-Type Doping of Sb2S3 Light-Harvesting Films Enabling High-Efficiency Planar Heterojunction Solar Cells. ACS Appl. Mater. Interfaces 2018, 10, 30314-30321.


Page 20 of 28

Page 21 of 28 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


(44) Berenguer, R.; Sieben, J. M.; Quijada, C.; Morallon, E. Pt- and Ru-Doped SnO2-Sb Anodes with High Stability in Alkaline Medium. ACS Appl. Mater. Interfaces 2014, 6, 22778-22789. (45) Scholes, G. D. Insights into Excitons Confined to Nanoscale Systems: Electron–Hole Interaction, Binding Energy, and Photodissociation. ACS Nano 2008, 2, 523-537. (46) Hewa-Kasakarage, N. N.; Kirsanova, M.; Nemchinov, A.; Schmall, N.; El-Khoury, P. Z.; Tarnovsky, A. N.; Zamkov, M. Radiative Recombination of Spatially Extended Excitons in (ZnSe/CdS)/CdS Heterostructured Nanorods. J. Am. Chem. Soc. 2009, 131, 1328-1334. (47) Xie, R.; Peng, X. G. Synthesis of Cu-doped InP Nanocrystals (d-dots) with ZnSe Diffusion Barrier as Efficient and Color-Tunable NIR Emitters. J. Am. Chem. Soc. 2009, 131,10645-10651. (48) Deng, Z. T.; Tang, F. Q.; Chen, D.; Meng, X. W.; Cao, L.; Zou, B. S. A Simple Solution Route to Single-Crystalline Sb2O3 Nanowires with Rectangular Cross Sections. J. Phys. Chem. B 2006, 110 , 18225-18230 (49) Klimov, V. I.; Mcbranch, D. W.; Leatherdal, C. A.; Bawendi, M. G. Electron and Hole Relaxation Pathways in Semiconductor Quantum Dots. Phys. Rev. B 1999, 60, 13740-13749. (50) Wang, X. Y.; Qu, L. H.; Zhang, J. Y.; Peng, X. G.; Xiao, M. Surface-Related Emission in Highly Luminescent CdSe Quantum Dots. Nano Lett. 2013, 3, 1103-1106.



(51) Xia, Z. G.; Wang, X. M.; Wang, Y. X.; Liao, L. B.; Jing, X. P. Synthesis, Structure, and Thermally Stable Luminescence of Eu2+-Doped Ba2Ln (BO3) 2Cl (Ln= Y, Gd and Lu) Host Compounds. Inorg. Chem. 2011, 50, 10134-10142. (52) Varshni, Y. P. Temperature Dependence of the Energy Gap in Semiconductors. physica 1967, 34, 149-154. (53) Qiao, J. W.; Ning, L. X.; Molokeev, M. S.; Chuang, Y. C.; Liu, Q. L.; Xia, Z. G. Eu2+ Site Preferences in the Mixed Cation K2BaCa(PO4)2 and Thermally Stable Luminescence. J. Am. Chem. Soc. 2018, 140 , 9730-9736. (54) Yuan, X.; Zheng, J. J.; Zeng, R. S.; Jing, P. T.; Ji, W. Y.; Zhao, J. L.; Yang, W. Y.; Li, H. B. Thermal Stability of Mn2+ ion Luminescence in Mn-Doped Core-Shell Quantum Dots. Nanoscale 2014, 6 , 300-307. (55) Lee, G. Y.; Han, J. Y.; Im, W. B.; Cheong, S. H.; Jeon, D. Y. Novel Blue-Emitting NaxCa1-xAl2-xSi2+xO8: Eu2+ (x = 0.34) Phosphor with High Luminescent Efficiency for UV-Pumped Light-Emitting Diodes. Inorg. Chem. 2012, 51, 10688-10694. (56) Liu, T. C.; Cheng, B. M.; Hu, S. F.; Liu, R. S. Highly Stable Red Oxynitride =-SiAlON: Pr3+ Phosphor for Light-Emitting Diodes. Chem. Mater. 2011, 23, 3698-3705. (57) Liu, L. P.; Peng, Q.; Li, Y. D. An Effective Oxidation Route to Blue Emission CdSe Quantum Dots. Inorg. Chem. 2008, 39 , 3182-3187. (58) Meissner, D.; Benndorf, C.; Memming, R. Photocorrosion of Cadmium Sulfide: Analysis by Photoelectron Spectroscopy. Appl. Surf. Sci. 1987, 27, 423-436.


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Page 25 of 28

transform pattern. C) HRTEM image of pristine doped CdS QDs with line-profile analysis at central (C2) and edge part (C3), C4 shows the FFT pattern of a single particle(scale bar:5 nm). D) EDS elemental mapping of one doped CdS QD. E) Raman spectrum of pristine doped CdS QDs; F) XRD patterns of as prepared pristine (blue line) and aged CdS into Sb2O3 coated of Ag+ doped CdS QDs (red line); G) HRTEM image of one CdS:Ag@CdS QD (scale bar:5 nm). H) FTIR spectra of as prepared pristine doped CdS QDs (black line) and aged CdS:Ag@Sb2O3 QDs (red line).

0.6 0.4 0.2

25500

25520

25540

25560

25580

Ag-S 2

1

0

25600

0

Energy(eV)

E (k)|

Sb K-edge

4

R(Å)

6

Sb-S 9

Sb2S3 Pristine Aged

0.6 0.4

|FT k

0.8

380

378

376

374

372

370

368

366

364

F

Sb2S3 Pristine Aged

Sb-O

Ag+ 3d3/2

Binding Energy (eV)

3

1.0

XANES

2

12

1.4

D1.2

Ag+ 3d5/2

Intensity (a.u.)

(k)| Ag foil Ag2S Pristine Aged

Ag foil Ag2S Pristine Aged

3

0.8

Ag-Ag

3

|FT k

XANES

1.0

0.0 25480

C

4

B

Ag K-edge

Intensity (a.u.)

A 1.2

6

3

Sb 3d5/2 Sb3+ 3d3/2 O 1s oxid O 1s abs.

0.2

0 30480

30500

30520

30540

30560

0

30580

1

2

3

G1.2

H8

Cd K-edge

(k)|

1.0

|FT k

CdS Pristine Aged

0.6 0.4

5

542

6

6

540

538

536

534

Cd-S 4

532

530

528

526

Binding Energy (eV)

I

CdS Pristine Aged

3

0.8

Cd2+ 3d3/2 Cd2+ 3d3/2

2

0.2 0.0 26680

4

R(Å)

Energy(eV)

Intensity (a.u.)

0.0 30460

XANES

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


26700

26720

26740

Energy(eV)

26760

26780

0 0

1

2

3

4

5

R(Å)

6

420

415

410

405

400

Binding Energy (eV)

Figure 3. (A) Ag K-edge XANES spectra of as prepared pristine CdS QDs, aged

CdS:Ag@ Sb2O3 QDs and references of Ag2S and Ag foil. (B) Fourier transforms of the EXAFS at the Ag K-edge (C) High resolution XPS spectrum of Ag 3d. (D) Sb K-edge XANES spectra of Sb2S3, and as prepared pristine CdS QDs and aged


395


CdS:Ag@Sb2O3 QDs. (E) Fourier transforms of the EXAFS spectra at the Sb K-edge. (F) High resolution XPS spectrum of Sb 3d. (G) Cd K-edge XANES spectra of standard CdS, and as prepared doped CdS QDs. (H) Fourier transforms of the EXAFS spectra at the Cd K-edge. (I) High resolution XPS spectrum of Cd 3d in as prepared CdS:Ag@Sb2O3 QDs. 687nm

1.0

Normalized Intensity

em

687nm ex

PL

PLE

0.8

430nm

0.6

132nm FWHM

0.4

UV 0.2

0.0 300

C

ex

ex

400

500

600

700

800

600

700

Wavelength (nm)

B

560nm

D

C

PL intensity (a.u.)

A

400nm

800

Wavelength (nm)

0.010

E

10000

F

1 = 1.32 s 66.60 %

0.005

Intensity (a.u.)

2 = 4.37 s 33.40 % 1000

0.000

A

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 26 of 28

1ps 5ps 10ps 100ps 1ns 7ns

-0.005

-0.010

PL 687nm 100

-0.015 10

-0.020

450

500

550

600

650

Wavelength (nm)

700

750

0

5

10

15

20

25

Time ( s)

Figure 4. Optical properties of CdS:Ag@Sb2O3 QDs. (A) Optical absorption and PL spectra of as-prepared CdS:Ag@Sb2O3 QDs. The blue line represents the PLE spectrum of the Ag+-PL of 687nm. (B) TA spectra for CdS:Ag@Sb2O3 QDs in toluene. (C) PL spectra of the CdS:Ag@Sb2O3 QDs under different energy excitation. The dashed line represents the bandgap excitation. (D) CIE diagram of as prepared CdS:Ag@Sb2O3 QDs. (E) PL decay curve of Ag+-PL measured at E5Kd

using

>#3d L excitation. (F) A schematic diagram demonstrating Ag+-dopant PL in CdS:Ag@Sb2O3 QDs.


Page 27 of 28

1.2

25 oC 40 oC 50 oC 75 oC 100 oC 125 oC 150 oC 175 oC 200 oC

B

CdS:Ag o

Intensity (a.u.)

25 C 50 oC 75 oC 100 oC 125 oC 150 oC 175 oC 200 oC

C

1.0

PL intensity /a.u.

CdS:Ag@Sb2O3

Intensity (a.u.)

A

CdS:Ag@Sb2O3

0.8

CdS:Ag 0.6

45%

0.4

32%

0.2 0.0

D

700

800

500

900

CdS:Ag@Sb2O3 25 oC 150 oC 200 oC

1.0 0.8 0.6 0.4 0.2 0.0 500

600

700

800

700

800

1.0

E

0.8

700

o

200 C 0.6

0.4

0.2

500

600

700

CdS:Ag@Sb2O3

675

650

800

CdS:Ag

50

Wavelength (nm) Slope =

Ln [(I0/It)-1]

6.3

200

625

900

I

H Slope =

150

F

CdS:Ag 25 oC 150 oC

Wavelength (nm) G

100

T/ oC

0.0 600

50

Wavelength (nm)

Wavelength (nm) Normalized PL Intensity (a.u.)

Normalized PL Intensity (a.u.)

1.2

600

PL Peak (nm)

500

Ln[(I0-It)-1]

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


100

150

200

T/ oC

6.06

CdS:Ag

CdS:Ag@Sb2O3 2.2

2.4

2.6

2.8

1000/T(K-1)

3.0

3.2

2.0

2.2

2.4

2.6

2.8

3.0

3.2

1000/T(K-1)

Figure 5. (A-B) Temperature-dependent PL spectra of CdS:Ag@Sb2O3 QDs and CdS:Ag QDs in the temperature range of 25 oC-200 oC. (C) The evolution of integrated PL intensity from 25 to 200 oC for CdS:Ag and CdS:Ag@Sb2O3 QDs. (D-E) Normalized PL spectra of CdS:Ag@Sb2O3 QDs and CdS:Ag at 25 oC, 150

oC

and

200 oC. (F) PL peak variation at 25 oC, 150 oC and 200 oC. (G-H) Activation energies for thermal quenching in CdS:Ag@Sb2O3 QDs and CdS:Ag QDs. (I) Configurational coordinate diagram that presents possible mechanisms of thermal quenching of Ag+ in the CdS host.



B

Intensity (a.u.)

0h 12h 30h

CdS:Ag@Sb2O3

C

1.0

0h 12h 30h

Intensity (a.u.)

CdS:Ag

Remnant PL

A

0.9 0.8 0.7 CdS:Ag@Sb2O3

0.6

CdS:Ag

0.5 600

700

0

800

500

Wavelength (nm)

700

10

800

S 2p

CdS:Ag@Sb2O3

E

after irradation

20

30

Irradation Time/h

Wavelength (nm)

F

S 2p O 1s oxid

Intensity (a.u.)

CdS:Ag

D

600

after irradation

before irradation

Intensity (a.u.)

500

Intensity (a.u.)

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 28 of 28

Sb 3d3/2

Sb 3d5/2

O 1s abs.

After UV irradation O 1s oxid

Sb 3d5/2

Sb 3d3/2 O 1s abs.

before irradation Before UV irradation 160

165

170

Binding Energy (eV)

175

160

165

170

175

543

Binding Energy (eV)

540

537

534

531

Binding Energy (eV)

Figure 6. (A-B) PL spectra of CdS:Ag and CdS:Ag@Sb2O3 QDs under UV irradiation for 0, 12 and 30 h. (C) Photostability of the CdS:Ag and CdS:Ag@Sb2O3 QDs. (D-E) Comparison of XPS spectra of S 2p in CdS:Ag QDs and CdS:Ag@Sb2O3 QDs before and after UV irradiation. (F) Sb 3d and O 1s XPS spectra revolution for as prepared CdS:Ag@Sb2O3 QDs before and after UV irradiation.


High-Performance Quantum Dots with Synergistic Doping and Oxide

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