Ligand-Free Nanocrystals of Highly Emissive Cs4PbBr6 Perovskite

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Ligand-Free Nanocrystals of Highly Emissive CsPbBr Perovskite Yuhai Zhang, Lutfan Sinatra, Erkki Alarousu, Jun Yin, Ahmed M. El-Zohry, Osman M. Bakr, and Omar F. Mohammed J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b01735 • Publication Date (Web): 23 Feb 2018 Downloaded from http://pubs.acs.org on February 24, 2018

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The Journal of Physical Chemistry

Ligand-Free Nanocrystals of Highly Emissive Cs4PbBr6 Perovskite Yuhai Zhang,†,‡ Lutfan Sinatra, §,† Erkki Alarousu,† Jun Yin,† Ahmed M. El-Zohry,† Osman M. Bakr,§, † Omar F. Mohammed*,† †

KAUST Solar Center, Division of Physical Sciences and Engineering, King Abdullah

University of Science and Technology, Thuwal,23955-6900, Kingdom of Saudi Arabia ‡Institute

for Advanced Interdisciplinary Research (IAIR), University of Jinan, Jinan, 250022,

Shandong Province, China §KAUST

Catalysis Center, Division of Physical Sciences and Engineering, King Abdullah

University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia

AUTHOR INFORMATION Corresponding Authors [email protected]

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ABSTRACT

Although ligands of long carbon chains are very crucial to form stable colloidal perovskite nanocrystals (NCs), they create a severe barrier for efficient charge injection or extraction in quantum dot based optoelectronics, such as light emitting diode (LED) or solar cell. Here, we report a new approach to prepare ligand-free perovskite NCs of Cs4PbBr6 with retained high photoluminescence quantum yield (PLQY: 44%). Such an approach involves a polar solvent (acetonitrile) and two small molecules (ammonium acetate and cesium chloride) which replace the organic ligand and still protect the nanocrystals from dissolution. The successful removal of hydrophobic-long ligands was evidenced by Fourier transform infrared (FTIR) spectroscopy, zeta potential analysis, and thermogravimetric analysis (TGA). Unlike conventional perovskite NCs that are extremely susceptible to polar solvents, the ligand-free Cs4PbBr6 NCs show robust resistance to polar solvents. Our ligand-free procedure opens many possibilities not only in material hybridization perspective, but also in optimizing charge injection and extraction in semiconductor quantum dot based optoelectronics applications.


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Introduction

All-inorganic perovskite NCs have garnered a broad range of interests in optoelectronic community due to their versatile electronic and optical properties,1-3 such as high photoluminescence (PL) quantum yield (>90%), tunable bandgap, and narrow full width at half maximum (FWHM, 170 meV) make a 5 ACS Paragon Plus Environment


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mystery of PL origin. Akkerman et al. and Quan et al. have argued that the impurity of CsPbBr3 phase (~10 nm in size) might be the origin of PL.24-27 However, none of them has provided any direct evidence of CsPbBr3 phase in either XRD or selective area electron diffraction (SAED) measurement, partially due to the labile nature of Cs4PbBr6 under electron irradiation. With the assistance of a Gatan K2 direct-detection camera, SAED (Figure 1, c and e) and high-resolution TEM (HRTEM) measurement were performed (Figure 1d, Figure S1) on a single Cs4PbBr6 NC under ultra-low dose of electrons (~1 electron.Å-2.s-1). All of the diffraction spots can be well assigned to hexagonal phase of Cs4PbBr6, indicating the absence of CsPbBr3 phase. The HRTEM image of a single emissive Cs4PbBr6 NC excludes the possibility of any inclusion of CsPbBr3 impurity on single-particle level, suggesting that the PL at 515 nm is inherent to these NCs which is consistent with the recent reports.28-31


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Figure 1. (a) Transimission electron microscopic (TEM) image of as-prepared Cs4PbBr6 NCs and (b) ligand-free NCs. Scale bars represent 500 nm. (c) Electron diffraction pattern of a cluster of ligand-free NCs. The brown dashed arrows represent those forbidden peaks in XRD measurement. (d) High-resolution K2-camera TEM image of a single Cs4PbBr6 NC. Scale bar is 5 nm. Its fast Fourior transformation (FFT) image was shown in (e), revealing a singlecrystal nature. (f) Photograph of a layered suspension of Cs4PbBr6 NCs in octane (OCT) and acetonitrile (ACN), respectively, under ambient light (left) and UV lamp (right) illumination. A clear interface indicates the immisable nature of non-polar (OCT) and polar solvent (ACN). The intense photoluminescene suggests a retained high PLQY after ligand removal. (g) XRD patterns of the as-prepared and ligand-free Cs4PbBr6 NCs, respectively, showing an identical phase indexed to a centrosymetric space group R-3c (167).

Figure 1g presents the XRD patterns of Cs4PbBr6 NCs before and after washing, revealing an identical phase of trigonal system with space group of R-3c (167). The retained pure phase indicates the robust resistance of Cs4PbBr6 NCs towards our washing procedure. It is worth noting that the XRD data again confirms the absence of CsPbBr3 phase. Akkerman et al., have argued that the quantity of CsPbBr3 impurity might be too minor (< 2 %) to be observed from XRD.24 To this end, we deliberately mixed 0.5 wt% CsPbBr3 NCs into Cs4PbBr6 NCs and performed XRD measurement. The characteristic peaks of CsPbBr3 NCs can be clearly observed



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(Figure S2), indicating that the absence of CsPbBr3 NCs in XRD can’t be ascribed to their minor quantity. To probe the surface property of Cs4PbBr6 NCs, a set of measurements, including FTIR, zetapotential, and TGA, were conducted with Cs4PbBr6 NC samples before and after the washing procedure (Figure 2, Figure S7). FTIR spectrum of oleic acid shows three characteristic peak at 1705 cm-1, 2852 cm-1 and 2922 cm-1, which are shared by the as-prepared Cs4PbBr6 NC, indicating the OA molecule as the ligand identity. After washing, all three peaks vanished, proving the successfully removal of OA. Along with the ligand removal, the surface charge was also changed from slight positive (3.9 ± 2.2 mV) to negative (-6.4 ± 3.4 mV) according to zetapotential measurement. The negative value indicates the replacement of OA by Cl- ions from the washing agent CsCl. It is worth noting that dichloromethane of medium polarity was used for zeta-potential measurement of both as-prepared and ligand-free Cs4PbBr6 NCs. Due to the small zeta-potential (< 10 mV), the colloidal stability of NC suspension is substantially low, which may pose barrier on making high-quality thin films. It should be noted that the ligand-free NCs become more hygroscopic when exposed in air (Figure S3), leading to less stability and faster PLQY decay as compared to their ligand-protected counterpart. To quantify the ligand removal efficiency, we conducted the TGA measurement in a temperature range from 20 oC to 500 oC (Figure 2c). The weight loss of samples from 240 oC to 460 oC is 1.94% and 0.12% for as-prepared and ligand-free NCs, respectively. Based on sphere assumption of NC shape, the ligand number density on surface was determined to be 0.5 /nm2 and 0.03 /nm2, suggesting a ligand removal efficiency as high as 94%. The minor weight loss of ligand-free NCs confirms that the negative charge of surface was induced by adhesion of Clinstead of acetate ions. It is worth pointing out that this washing procedure is not a universal


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Figure 2. (a) Fourier transform infrared (FTIR) spectra of oleic acid, as-prepared and ligandfree Cs4PbBr6 NCs, clearly showing the removal of oleic acid after washing procedure. (b) zeta potential of Cs4PbBr6 NCs before and after washing procedures, indicating opposite charging on nanocrystal surface. (c) Thermogravimetric analysis of as-prepared and ligand-free Cs4PbBr6 NCs. Dashed lines denote the temperature interal from 260 oC to 460 oC. (d) UV-Vis absorption (dashed curve) and PL (solid curve) spectra of Cs4PbBr6 NCs suspensions before and after removal of capping ligands; note that both of the suspensions show an extended Urbach tail. strategy for other perovskite NCs. In an attempt to remove OA ligands from CsPbBr3 NCs, we found that this washing procedure decomposed CsPbBr3 into non-emissive Cs4PbBr6 in the sonication stage (Figure S4). To probe the optical properties of Cs4PbBr6 NCs, UV-Vis absorption and PL spectra measurement was conducted (Figure 2d). The absorption peak of as-prepared NC shows a 12-nm blue shift from 315 to 303 nm after ligand removal, which might be induced by partial alloying of mixed Br-Cl halides.24 Interestingly, the PL peak position at 515 nm remains unaltered. Such inconsistency between absorption and PL behavior indicates that the intrinsic bandgap transition of Cs4PbBr6 does not directly give rise to the green emission. Besides, we have excluded the existence of CsPbBr3 impurity based on the aforementioned measurements. Therefore, we speculate that the PL of Cs4PbBr6 NCs might originate from other “color centers” such as Br9 ACS Paragon Plus Environment


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Figure 3. 2D pseudo-color transient emission map of (a) as-prepared Cs4PbBr6 NCs and (b) ligand-free NCs, showing a decreased lifetime after ligand removal. (c) Histogram of particle size of as-synthesized, fresh ligand-free (1 hour storage), and aged ligand-free NCs (24 hour storage). 200 particles were counted for each sample. The increase of particle size indicates that the ligand-free NCs experience Ostwald ripening when keeping in polar solvent. (d) Schematic shows a possible Br- vacancy (VBr-) in lattice (left panel, detailed DFT calculation for vacancy level is ongoing), and the possible distribution of color centers (r2 < r1) in particles before and after ligand removal (right panel). vacancies or the self-trapping states (Pb23+).32-35 It is worth noting that a long Urbach tail was observed in absorption spectra, indicating the presence of vacancy or possible lattice disorder. Importantly, the structural integrity of Cs4PbBr6 NCs ensures a retained high PLQY after ligand removal. Due to the severe light scattering of NC suspension, the PLQY was measured by the use of an integrated sphere (Figure S5). The PLQY was determined to be 68% and 44% before and after ligand removal. To understand the deactivation pathway of excited self-trapping states, PL lifetimes were measured using Streak camera with picosecond temporal resolutions 10 ACS Paragon Plus Environment

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(Figure 3, a and b, Figure S8). The lifetime of as-prepared Cs4PbBr6 NCs can be well fitted with bi-exponential function, including a short component of 2.6 ns and a long component of 13.9 ns. The short one is ascribable to the aggregation of color centers (defect levels) where cross relaxation effectively increases the deactivation rate (Figure 3d), alike to the concentration quenching in lanthanide doped nanocrystals;36 meanwhile, the long one is likely the intrinsic decay of discrete individual color center. The ligand removal process decreases the short component from 2.6 ns to 1.6 ns, while the long component remains unchanged (13.9 ns) which evidenced its intrinsic nature of individual color center.

Discussion

The shorten lifetime indicates a closer distance amongst color centers, and an ensuing higher concentration of those emitting centers in ligand-free Cs4PbBr6 NCs. To understand how the particles evolve before and after ligand removal, size histogram of NCs was analyzed against storage time in acetonitrile (Figure 3c, Figure S6). The average size of as-prepared NCs is about 90 nm, which increased to 97 nm after ligand removal in 1 hour. Further storage of 24 hour leads to an even larger particle size of 139 nm, which indicates that the ligand-free NCs experience severe Ostwald ripening in polar solvent. It is likely that polar-solvent storage gives rise to the higher concentration of emitting centers (r2 < r1) and an ensuing shorten lifetime (Figure 3d). This proposition is in line with the fact that all those emissive Cs4PbBr6 phases, including powers and NCs, are generated in the presence of a polar solvent (i.e. DMF) while those non-emissive are synthesized in an environment of non-polar solvent (i.e. octadecene).25, 28-29



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Conclusion

In conclusion, we developed an efficient washing procedure to generate ligand-free Cs4PbBr6 perovskites NCs with retained high PLQY. Both the surface and the optical properties of the NCs were systematically investigated using both steady-state and time-resolved techniques. Additionally, the mystery of

the PL origin of insulating Cs4PbBr6 was also explained with a

color center proposition. Our work removes one barrier of charge transport in optoelectronic devices associating with quantum dots with long carbon-chain ligands, and may also inspire that work in perovskite based material hybridization.

AUTHOR INFORMATION Corresponding Authors *O.F.M: Email: [email protected] Notes The authors declare no competing financial interests. ACKNOWLEDGMENT This work was financially supported by King Abdullah University of Science and Technology (KAUST). ASSOCIATED CONTENT


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Supporting Information. Experimental details for material synthesis, large area HRTEM image, XRD data, and TEM images showing the size evolution during storage. REFERENCES (1) Akkerman, Q. A.; D'Innocenzo, V.; Accornero, S.; Scarpellini, A.; Petrozza, A.; Prato, M.; Manna, L. Tuning the Optical Properties of Cesium Lead Halide Perovskite Nanocrystals by Anion Exchange Reactions. J. Am. Chem. Soc. 2015, 137, 10276-10281. (2) Ravi, V. K.; Markad, G. B.; Nag, A. Band Edge Energies and Excitonic Transition Probabilities of Colloidal CsPbX3 (X = Cl, Br, I) Perovskite Nanocrystals. ACS Energy Lett. 2016, 1, 665-671. (3) Shamsi, J.; Dang, Z. Y.; Ijaz, P.; Abdelhady, A. L.; Bertoni, G.; Moreels, I.; Manna, L. Colloidal CsX (X = CI, Br, I) Nanocrystals and Their Transformation to CsPbX3 Nanocrystals by Cation Exchange. Chem. Mater. 2018, 30, 79-83. (4) Chung, H.; Jung, S. I.; Kim, H. J.; Cha, W.; Sim, E.; Kim, D.; Koh, W. K.; Kim, J. Composition ‐ Dependent Hot Carrier Relaxation Dynamics in Cesium Lead Halide (CsPbX3, X= Br and I) Perovskite Nanocrystals. Angew. Chem. 2017, 129, 4224-4228. (5) Swarnkar, A.; Chulliyil, R.; Ravi, V. K.; Irfanullah, M.; Chowdhury, A.; Nag, A. Colloidal CsPbBr3 Perovskite Nanocrystals: Luminescence Beyond Traditional Quantum Dots. Angew. Chem. 2015, 127, 15644-15648. (6) Begum, R.; Parida, M. R.; Abdelhady, A. L.; Murali, B.; Alyami, N. M.; Ahmed, G. H.; Hedhili, M. N.; Bakr, O. M.; Mohammed, O. F. Engineering Interfacial Charge Transfer in CsPbBr3 Perovskite Nanocrystals by Heterovalent Doping. J. Am. Chem. Soc. 2017, 139, 731-737. (7) Nedelcu, G.; Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Grotevent, M. J.; Kovalenko, M. V. Fast Anion-Exchange in Highly Luminescent Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, I). Nano Lett. 2015, 15, 5635-5640. (8) Yin, J.; Maity, P.; De Bastiani, M.; Dursun, I.; Bakr, O. M.; Brédas, J.-L.; Mohammed, O. F. Molecular Behavior of Zero-Dimensional Perovskites. Sci. Adv. 2017, 3, e1701793.



Page 14 of 17

(9) Gonzalez-Pedro, V.; Juarez-Perez, E. J.; Arsyad, W.-S.; Barea, E. M.; Fabregat-Santiago, F.; Mora-Sero, I.; Bisquert, J. General Working Principles of CH3NH3PbX3 Perovskite Solar Cells. Nano Lett. 2014, 14, 888-893. (10) Swarnkar, A.; Marshall, A. R.; Sanehira, E. M.; Chernomordik, B. D.; Moore, D. T.; Christians, J. A.; Chakrabarti, T.; Luther, J. M. Quantum dot–induced phase stabilization of α-CsPbI3 perovskite for high-efficiency photovoltaics. Science 2016, 354, 92-95. (11) Li, J.; Xu, L.; Wang, T.; Song, J.; Xue, J.; Dong, Y.; Cai, B.; Shan, Q.; Han, B.; Zeng, H. 50 ‐ Fold EQE Improvement up to 6.27% of Solution ‐ Processed All ‐ Inorganic Perovskite CsPbBr3 QLEDs via Surface Ligand Density Control. Adv. Mater. 2017, 29, 1603885-1603894. (12) Rong, Y.; Hu, Y.; Ravishankar, S.; Liu, H.; Hou, X.; Sheng, Y.; Mei, A.; Wang, Q.; Li, D.; Xu, M. Tunable Hysteresis Effect for Perovskite Solar Cells. Energy Environ. Sci 2017, 10, 2383-2391. (13) Liu, Z.; Bekenstein, Y.; Ye, X.; Nguyen, S. C.; Swabeck, J.; Zhang, D.; Lee, S.-T.; Yang, P.; Ma, W.; Alivisatos, A. P. Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals to Lead Depleted Cs4PbBr6 Nanocrystals. J. Am. Chem. Soc. 2017, 139, 5309-5312. (14) Quan, L. N.; Yuan, M.; Comin, R.; Voznyy, O.; Beauregard, E. M.; Hoogland, S.; Buin, A.; Kirmani, A. R.; Zhao, K.; Sargent, E. H. Ligand-Stabilized Reduced-Dimensionality Perovskites. J. Am. Chem. Soc. 2016, 138, 2649-2655. (15) Sun, S.; Yuan, D.; Xu, Y.; Wang, A.; Deng, Z. Ligand-Mediated Synthesis of ShapeControlled Cesium Lead Halide Perovskite Nanocrystals via Reprecipitation Process at Room Temperature. ACS Nano 2016, 10, 3648–3657. (16) Pan, J.; Quan, L. N.; Zhao, Y.; Peng, W.; Murali, B.; Sarmah, S. P.; Yuan, M.; Kim, D. H.; H. Sargent, E.; M. Bakr, O. Highly Efficient Perovskite‐Quantum‐Dot Light‐Emitting Diodes by Surface Engineering. Adv. Mater. 2016, 28, 8718-8725. (17) Ning, Z.; Gong, X.; Comin, R.; Walters, G.; Fan, F.; Voznyy, O.; Yassitepe, E.; Buin, A.; Hoogland, S.; Sargent, E. H. Quantum-Dot-in-Perovskite Solids. Nature 2015, 523, 324332.


Page 15 of 17 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


(18) Kim, Y.; Yassitepe, E.; Voznyy, O.; Comin, R.; Walters, G.; Gong, X.; Kanjanaboos, P.; Nogueira, A. F.; Sargent, E. H. Efficient Luminescence from Perovskite Quantum Dot Solids. ACS Appl. Mater. Interfaces 2015, 7, 25007-25013. (19) Zhang, Y.; Saidaminov, M. I.; Dursun, I.; Yang, H.; Murali, B.; Alarousu, E.; Yengel, E.; Alshankiti, B. A.; Bakr, O. M.; Mohammed, O. F. Zero-Dimensional Cs4PbBr6 Perovskite Nanocrystals. J. Phys. Chem. Lett. 2017, 8, 961-965. (20) Chen, D.; Wan, Z.; Chen, X.; Yuan, Y.; Zhong, J. Large-scale Room-Temperature Synthesis and Optical Properties of Perovskite-Related Cs4PbBr6 Fluorophores. J. Mater. Chem. C 2016, 4, 10646-10653 (21) Yang, H.; Zhang, Y.; Pan, J.; Yin, J.; Bakr, O. M.; Mohammed, O. F. Room-temperature Engineering of All-inorganic Perovskite Nanocrsytals with Different Dimensionalities. Chem. Mater. 2017, 29, 8978-8982. (22) Finsy, R. On the Critical Radius in Ostwald Ripening. Langmuir 2004, 20, 2975-2976. (23) Saidaminov, M. I.; Almutlaq, J.; Sarmah, S.; Dursun, I.; Zhumekenov, A. A.; Begum, R.; Pan, J.; Cho, N.; Mohammed, O. F.; Bakr, O. M. Pure Cs4PbBr6: Highly Luminescent ZeroDimensional Perovskite Solids. ACS Energy Lett. 2016, 1, 840-845. (24) Akkerman, Q. A.; Park, S.; Radicchi, E.; Nunzi, F.; Mosconi, E.; De Angelis, F.; Brescia, R.; Rastogi, P.; Prato, M.; Manna, L. Nearly Monodisperse Insulator Cs4PbX6 (X = Cl, Br, I) Nanocrystals, Their Mixed Halide Compositions, and Their Transformation into CsPbX3 Nanocrystals. Nano Lett. 2017, 17, 1924-1930. (25) Quan, L. N.; Quintero-Bermudez, R.; Voznyy, O.; Walters, G.; Jain, A.; Fan, J. Z.; Zheng, X.; Yang, Z.; Sargent, E. H. Highly Emissive Green Perovskite Nanocrystals in a Solid State Crystalline Matrix. Adv. Mater. 2017, 29, 1605945. (26) Xu, J.; Huang, W.; Li, P.; Onken, D. R.; Dun, C.; Guo, Y.; Ucer, K. B.; Lu, C.; Wang, H.; Geyer, S. M. Imbedded Nanocrystals of CsPbBr3 in Cs4PbBr6: Kinetics, Enhanced Oscillator Strength, and Application in Light‐Emitting Diodes. Adv. Mater. 2017, 29, 1703703. (27) Palazon, F.; Urso, C.; De Trizio, L.; Akkerman, Q.; Marras, S.; Locardi, F.; Nelli, I.; Ferretti, M.; Prato, M.; Manna, L. Postsynthesis Transformation of Insulating Cs4PbBr6



Page 16 of 17

Nanocrystals into Bright Perovskite CsPbBr3 through Physical and Chemical Extraction of CsBr. ACS Energy Lett. 2017, 2, 2445-2448. (28) Hu, M.; Ge, C.; Yu, J.; Feng, J. Mechanical and Optical Properties of Cs4BX6 (B = Pb, Sn; X = Cl, Br, I) Zero Dimension Perovskites. J. Mater. Chem. C 2017, 121, 27053-27058. (29) Zhang, H.; Liao, Q.; Wu, Y.; Chen, J.; Gao, Q.; Fu, H. Pure Zero-Dimensional Cs4PbBr6 Single Crystal Rhombohedral Microdisks with High Luminescence and Stability. Phys. Chem. Chem. Phys. 2017, 19, 29092-29098. (30) Yang, L.; Li, D.; Wang, C.; Yao, W.; Wang, H.; Huang, K. Room-Temperature Synthesis of Pure Perovskite-Related Cs4PbBr6 Nanocrystals and Their Ligand-Mediated Evolution into Highly Luminescent CsPbBr3 Nanosheets. J. Nanopart. Res. 2017, 19, 258-271. (31) Seth, S.; Samanta, A. Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related Cs4PbBr6 Microdisks: Synthesis and Single-Particle Imaging Study. J. Phys. Chem. Lett. 2017, 8, 4461-4467. (32) Yamasaki, Y.; Ohno, N. Self-Trapped Excitons in Orthorhombic SnBr2. Int. J. Mod. Phys. B 2001, 15, 4009-4012. (33) Kitaura, M.; Nakagawa, H. Luminescence due to Dimer Type Self-Trapped Excitons in Lead Halides. J. Electron. Spectrosc. Relat. Phenom. 1996, 79, 171-174. (34) Yin, J.; Zhang, Y.; Bruno, A.; Soci, C.; Bakr, O. M.; Brédas, J.-L.; Mohammed, O. F. Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals. ACS Energy Lett. 2017, 2, 2805-2811. (35) Zhou, C.; Tian, Y.; Wang, M.; Rose, A.; Besara, T.; Doyle, N. K.; Yuan, Z.; Wang, J. C.; Clark, R.; Ma, B. Low-Dimensional Organic Tin Bromide Perovskites and Their Photoinduced Structural Transformation. Angew. Chem. Int. Ed. 2017, 56, 9018-9022. (36) Lu, Y.; Zhao, J.; Zhang, R.; Liu, Y.; Liu, D.; Goldys, E. M.; Yang, X.; Xi, P.; Sunna, A.; Lu, J. Tunable Lifetime Multiplexing Using Luminescent Nanocrystals. Nat. Photonics 2014, 8, 32-36.


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Ligand-Free Nanocrystals of Highly Emissive Cs4PbBr6 Perovskite

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