Growth Processes of LuF3 Upconversion Nanoflakes with the

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The Growth Processes of LuF3 Upconversion Nanoflakes with Assistance of Amorphous Nanoclusters Ting Wang, Yue Lin, Wei Lu, Xuyun Guo, Jianbei Qiu, Xue Yu, Qiuqiang Zhan, Siu Fung Yu, and Xuhui Xu ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.9b01106 • Publication Date (Web): 10 Jul 2019 Downloaded from pubs.acs.org on July 17, 2019

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ACS Applied Nano Materials

The Growth Processes of LuF3 Upconversion Nanoflakes with Assistance of Amorphous Nanoclusters Ting Wang1, 2, Yue Lin3*, Wei Lu2, Xuyun Guo2, Jianbei Qiu1*, Xue Yu1, Qiuqiang Zhan4, Siu Fung Yu2*, Xuhui Xu1* 1Faculty

of Materials Science and Engineering, Kunming University of Science and Technology, Kunming, Yunnan Province 650093, People’s Republic of China

2Department 3Hefei

4Centre

of Applied Physics, The Hong Kong Polytechnic University, Hong Kong, People’s Republic of China

National Laboratory for Physical Science at the Microscale, University of Science and Technology of China, Hefei, Anhui Province 230026, People’s Republic of China for Optical and Electromagnetic Research, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou Province, 510006 People’s Republic of China

*corresponding author: Xuhui Xu: [email protected]; Siu Fung Yu: [email protected]; Jianbei Qiu: [email protected]; Yue Lin: [email protected]

Abstract: Improvement of facile synthesis strategy is an effective way to tune the optical properties of lanthanide-doped upconversion nanoparticles. However, it is necessary to directly study the growth process in order to control the formation structure of the nanoparticles. Here, we propose to use in situ TEM imaging technique to observe the growth kinetics of LuF3 upconversion nanoflakes. It is discovered that the suppression of surface amorphous clusters, which act as the quenching centers, during the flake-to-flakes growth process of nanoflakes can significantly improve the upconversion efficiency. Therefore, by controlling the concentration of amorphous nanoclusters in the precursor solution, we can manipulate the morphology and fabricate LuF3 nanoflakes with maximized upconversion emission intensity. Keywords: upconversion, LuF3 nanoflakes, amorphous nanoclusters, in situ TEM imaging

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Introduction Lanthanide ions (Ln3+= Er3+, Tm3+, Yb3+, etc.) doped upconversion nanoparticles have attracted enormous attention for the applications in optical imaging-guided bioimaging, therapeutics, anti-counterfeiting, and active photonic devices.1-5 Despite the desirable optical features of these nanoparticles, there have been no investigations on the relationship between the growth kinetics and upconversion emission characteristics. If the growth process of the nanoparticles can be observed directly, we can obtain a facile synthesis strategy to control the structural formation of nanoparticles with desired upconversion emission properties. Recently, in situ transmission electron microscopy (TEM) techniques, which provide a direct image platform to visualize nanomaterials on the nanometer scale, is used to study the growth process of metallic and metal-oxide nanomaterials.6-8 However, in situ TEM imaging can provide only highresolution 2D images due to the shallow depth of field so that imaging of nanoparticles with a curved surface is not preferred. Here, we study the growth kinetics of Er3+, Yb3+ co-doped LuF3 nanoflakes via in-situ TEM imaging. The reasons to choose nanoflakes are 1) the nanoflakes have a flat surface which can be focused to a sharp image9 and 2) the nanoflakes have a thickness of ~5 nm which is thick enough to accommodate Ln3+. For real-time observation of the growth process of the nanoflakes in high resolution, a small drop of precursor solution is placed on a copper mesh to perform in situ TEM imaging. Furthermore, we apply electron-beam irradiation to stimulate the growth of nanoflakes from the dried precursor in a vacuum environment at room temperature. Here, it is observed that the amorphous clusters, which act as the metastable state of the nanoparticles, can be crystallized under electron beam irradiation. On the other hand, we use the wet-chemical heat-treatment method to remove the surface amorphous clusters of the upconversion nanoflakes during the annealing process.10 It can be shown that the upconversion nanoflakes exhibit perfectly crystallized structure even over large surface area with upconversion emission intensity to be improved by more than 10 times at room temperature under 980 nm continue wavelength laser pump. We verify that the consumption of surface amorphous cluster, which acts as impurity and quenching centers, enhances the upconversion energy transfer process and upconversion efficiency.

Results and discussion 2


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Figure 1 TEM images LuF3: Yb3+, Er3+ upconversion nanoflakes at 290 oC for (a) 60, (b) 90, (c) 120, and (d) 150 mins reaction time. Scale bars, 50nm. (e) Photoluminescence spectra of the LuF3: Yb3+, Er3+ upconversion nanoflakes under 980 nm excitation at room temperature. The LuF3: Yb3+, Er3+ upconversion nanoflakes were synthesized at different temperatures via co-precipitation method11. It is found that the monodispersed nanoflakes with good upconversion properties and well-morphology were obtained at an optimum reaction temperature of 290 oC. Furthermore, we repeated synthesizing the LuF3 nanoflakes at 290 oC for different reaction time and the corresponding TEM images are shown in Figure 1. When the reaction time is 60 min, the LuF3 nanoflakes with different sizes are obtained. For reaction time increase to 90 min, uniform distribution of LuF3 nanoflakes is achieved. With further increase of reaction time, the nanoflakes growth and agglomerate together. The photoluminescence (PL) spectra shown that the sample synthesized at 290 oC for 90 min have the highest emission intensity, see Figure 1e. Hence, the optimum temperature and time to grow LuF3:Yb3+, Er3+ nanoflakes with uniform size and high-optical-quality is found to be 290 oC and 90 min respectively. Figure 2 shows the TEM and selected area electron diffraction (SAED) images of a LuF3:Yb3+, Er3+ nanoflake obtained from the optimized growth conditions (i.e. 290 oC, 90 min). The HR-TEM image (Figure 2a) clearly shows the lattice fringes at the interior and edges of the nanoflake. The lattice fringes display the typical D-spacing of ~0.361 and ~0.338 nm which corresponding to the (101) and (020) crystal planes of LuF3 respectively. The concentric 3



diffraction spots observed from the SAED pattern (Figure 2b) correspond to the specific (101) and (020) planes of the LuF3 lattice. These demonstrate the monocrystalline nature of the nanoflake. X-ray diffraction (XRD) (Figure S1) and EDS spectra (Figure S2) have indicated that the nanoflakes, which have a thickness of about 4 nm (Figure S3), are made from LuF3. The average size (i.e. maximum diagonal length) of the nanoflakes obtained from the optimized growth conditions is found to be about 23 nm, see Figure 2c. In order to further depict the morphology of the as-synthesized LuF3 nanoflake, HAADF-STEM image was measured (Figure 2d). It is observed that there are some amorphous nanoclusters adhered to the edge of the nanoflake. Figure 2e-2g show the atomic models related to the regions of the nanoflakes as indicated by the arrows (Figure 2d). The well-organized atoms crystalize with (101) plane (green arrow) is observed in the interior of the nanoflake (Figure 2g). However, crystallization is partially achieved at the edge of the nanoflake at the (020) crystal plane (cyan arrow) with some disordered amorphous clusters (magenta arrow) or even single atoms (orange circles). The high density of impurities and imperfect crystal lattices at the surface could result in the low upconversion energy transfer efficiency and high frequency of nonradioactive transitions.12 Thus, we conclude that the amorphous clusters at the surface are the dominant impurities which need to be eliminated.

Figure 2 (a) HRTEM and (b) SAED images of a LuF3: Yb3+, Er3+ nanoflake obtained under the optimized fabrication conditions. (c) The size distribution of the nanoflakes obtained at the optimized condition; (d) Atomic-resolution crystal structure image of the as-synthesized LuF3 nanoflake. The inset is the magnifying diagram of olive rectangular and the orange circles 4


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present the single atoms. The atomic model of (e), (f) and (g) is the corresponding regions as indicated by arrows in (d), respectively.

In order to study the growth process of the LuF3 nanoflakes, precursor state of LuF3 (amorphous clusters without crystallizing) were obtained by the co-precipitation method with shorter reaction time (i.e. 30 min). According to the high-angle annular dark-field (HAADF) scanning transmission electron microscope (STEM) and fast-Fourier transform (FFT) images given in Figure 3a, the amorphous structure of LuF3 shows no information of crystal-lattice fringes and the energy-dispersive X-ray spectroscopy (EDS) spectrum displays mainly Lu, F, Yb, Er elements (Figure S4 and Table S1). The precursors were then dispersed in absolute ethyl alcohol and dripped onto the copper mesh for TEM observation. Under electron-beam radiation, crystallization of LuF3 nanostructure was realized (Figure 3b, movie S1). Figure 3b shows the high-resolution (HR) TEM image of a LuF3 amorphous nanocluster. By prolonging the exposure time, the amorphous nanocluster gradually crystallizes and grows to form a nanoflake. These have been verified by their corresponding FFT and inverse FFT (IFFT) images. (Figure S5-S7). We found that the amorphous nanocluster undergoes crystallizing in both horizontally and longitudinally direction under the influence of electron-beam irradiation. Furthermore, the surrounding amorphous nanoclusters attach to the edges of the crystallized region of the nanoflake (Figure 3c and see movie S2 for details) is recognized. These studies clearly manifest that the growth of LuF3 nanoflakes is mainly determined by the presence of amorphous nanoclusters. It must be noted that electron-beam irradiation has influence on the crystallization rate of the LuF3 nanoflakes if the electron beam density is greater than 2.5 A/cm2 (Figure S8).The dynamic process of amorphous clusters joining two adjacent upconversion nanoflakes together to promote the growth which can be studied by in situ TEM technology as shown in Figure 3d (movie S3). At the initial stage, amorphous clusters attach to the edge at the lowerright direction of nanoparticle 3 and then crystallize under the electron-beam irradiation. Subsequently, the nanoparticle 3 gradually conjugates with nanoparticle 4 and finally get together to accomplish edge-to-edge attachment process. The insignificant distance change between the nanoflakes 4 and 5 suggests these nanoflakes are stationary. The decrease in distance between upconversion nanoflakes 3 and 4 indicates that the amorphous nanocluster acts as a ‘glue’ to fill the gap between two nanoflakes together to form a bigger nanoparticle. 5



The connection can also be proved by Figure S9 and S10. These results demonstrate that the amorphous clusters which can be regarded as a binder between two nanoflakes play a key role in the growth process. This phenomenon can be also proved by ref.13

Figure 3 (a) HAADF-STEM image of the LuF3 amorphous cluster, the inset is the corresponding fast Fourier transform (FFT). (b) Sequential time-resolved in-situ TEM images showing the nucleation process of LuF3 nanoparticle from the metastable state. (c) Sequences of in situ TEM images indicate the growth of LuF3. Scale bar is 2nm. (Electron beam density 4.8 A/cm2). (d) Sequential in situ HRTEM images shown the details particle attachment process of the two upconversion nanoflakes with the assistance of the amorphous nanoclusters at the edges of the upconversion nanoflakes. Scale bar is 5nm.

We propose to use the wet-chemical heat-treatment method to manipulate the morphology of the LuF3 upconversion nanoflakes (Figure 4a). It is necessary to avoid random attachment of amorphous nanoclusters in term of the flakes growth process(Figure S11-S12), so the sample of LuF3 upconversion nanoflakes were centrifuged and washed for 4~5 times, and then treated by the same wet chemical heat treatment to fabricate the uniform upconversion nanoflakes. 6


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The as-synthesized LuF3 upconversion nanoflakes, which were obtained at the optimized growth conditions, were centrifuged and washed before performing wet-chemical heattreatment at 240 oC for 90 min (Figure 4a). The required LuF3 upconversion nanoflakes were synthesized by co-precipitation – step. The reaction solution was centrifuged and washed for several times to separate supernatant fluid and precipitated upconversion nanoflakes – step . It be noted that redundant amorphous nanoclusters in the liquid solution are need to be washed in step. Subsequently, the LuF3 upconversion nanoflakes were annealed by wet chemical heat treatment method at 240 oC for 90 min – step . Finally, the upconversion nanoflakes with larger in size are obtained after self-assembly in step . The XRD pattern (Figure S13) show that after the wet-chemical heat-treatment, there is no phase changes. Figure 4b shows the TEM image of the LuF3 upconversion nanoflakes with perfect crystallization configuration without any impurities (Figure 4c) after wet-chemical heat-treatment. The TEM image displays that the well mono-dispersed regular flaky LuF3 possess an average size around 40 nm (Figure 4d). The crystallinity of the LuF3 flakes is improved and there is no extra amorphous clusters after wet-chemical heat-treatment method, especially at the edge of LuF3 flakes.

Figure 4 (a) Schematic illustration of the co-precipitation and the wet chemical heat treatment method for the synthesis of LuF3 upconversion nanoflakes. Typical (b) low resolution, (c) HRTEM images, and (c) corresponding size distribution of LuF3: Yb3+, Er3+ upconversion 7



nanoflakes after wet-chemical heat-treatment at 240 oC for 90 min. (e) Raman spectra; (f) emission spectra of LuF3 upconversion nanoflakes before and after wet-chemcail heattreatment method under 980 nm excitation at room temperature.

In Figure 4c, the HADDF-STEM image of the single LuF3 shows different orientations, ~0.361, ~0.338 ~0.361 nm which corresponding to the (101), (020) and (410) respectively, which may be due to insufficient energy of the system. In addition, the amorphous clusters at edges of flakes have been crystallized, this is because that the amorphous clusters around the flakes is converted from the metastable state (amorphous state) to the stability state (crystal state) during the wet-chemical heat-treatment method. Hence, concentration of the amorphous clusters in the liquid can be used to manipulate the morphology of the upconversion nanoflakes. Raman spectra of the LuF3: Yb3+, Er3+ upconversion nanoflakes shown in Figure 4e demonstrates that the total vibration frequencies of oleic acids molecules and (Yb···O) coordination is greatly reduced due to the complete exhaustion of amorphous nanoclusters after the attachment process.14 The edge-to-edge attachment process between two adjacent upconversion nanoflakes underwent wet-chemical heat-treatment is based on the consumption of amorphous nanoclusters. Figure 4f plots the PL spectra of the LuF3:Yb3+, Er3+ before and after wetchemical heat-treatment method under 980 nm excitation at room temperature. The LuF3:Yb3+, Er3+ upconversion nanoflakes after the wet-chemical heat-treatment exhibit enhancement of PL emission intensity when compared to that before the wet-chemical heat-treatment. This is due to the removal of the amorphous structure, which acts as the quenching center at the surface.

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Figure 5. (a) The mechanism of the wet-chemical heat treatment method on the revised the surface defect, green and orange spheres are the amorphous cluster and crystallized phase respectively. (b) and (c) show super-resolution image of Yb3+-Er3+ co-doped LuF3 nanocrystal before and after the wet-chemical heat-treatment method captured by using super-resolution microscopy and the three-dimensional representation of the wide-field upconversion emission image under 980nm excitation. (d) and (e) show the intensity recording over the number of scans under 980nm excitation solely for the selected areas.

The detail growth mechanism of the nanoflakes can be explained in Figure 5a. In the initial stage (), upconversion nanoflakes without aggregation are obtained, however, amorphous clusters adhered to the edge of upconversion nanoflakes and randomly dispersed in the asobtained solution are also observed. After the removal of the dissociative amorphous cluster in the solution, while the amorphous clusters adhered to the flakes is removed ( ② ), particles 9



attachment process lead the nanoparticles attachment with the assistance of amorphous clusters (③). Finally, uniform nanoflakes are realized (④). Therefore, the wet-chemical heat-treatment method is explored to control the LuF3 nanoflakes growth process. In this process, the amorphous clusters can transform from metastable state to stability stage, which may contribute to the improvement of optical properties. So, the upconversion single upconversion nanoflake emission are measured under 980nm excitation by using the high resolution microscopy (Figure S15). According to the compared three-dimensional representation of the wide-field upconversion emission image of the nanoparticle as well as the intensity recording for the selected area before and after the wet-chemical heat-treatment, the upconversion emission intensity of the single nanoflakes can be increased more than 10 times during the wet-chemical heat-treatment (Figure 5b-4e).

Conclusions In summary, we demonstrate the enhancement of upconversion emission intensity from the lanthanide doped LuF3 upconversion nanoflakes via the use of wet-chemical heattreatment method. The improvement of optical emission can be explained by the crystallization of surface amorphous clusters of the nanoflakes. This is because the surface amorphous clusters, which act as quenching centers, can be crystallized after the wet-chemical heat-treatment. In fact, this explanation is verified by direct observation on the growth process of nanoflakes throught the use of in situ TEM imaging technique.Here, by controlling the concentration of amorphous nanoclusters in the precursor solution, we can manipulate the morphology of LuF3 upconversion nanoflakes. Under 980 nm CW laser excitation, the upconversion emission intensity can be increased by an order of magnitude.

Acknowledgment This work was supported by Science and Technology Projects of Shenzhen (JCYJ20170818105010341), National Nature Science Foundation of China (61775187, 10


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61565009, 11664022), the Foundation of Natural Science of Yunnan Province (2016FB088), the Reserve talents project of Yunnan Province (2017HB011), and the Young Talents Support Program of Faculty of Materials Science and Engineering, Kunming University of Science and Technology (14078342).

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Ref: 1.

Zhou, B.;

Shi, B.;

Jin, D.; Liu, X., Controlling upconversion nanocrystals for emerging

applications. Nature Nanotechnology 2015, 10, 924. 2.

Wang, H.-Q.;

Batentschuk, M.;

Osvet, A.; Pinna, L.; Brabec, C. J., Rare-Earth Ion Doped Up-

Conversion Materials for Photovoltaic Applications. Advanced Materials 2011, 23 (22‐23), 2675-2680. 3.

Heer, S.;

Kömpe, K.;

Güdel, H. U.; Haase, M., Highly Efficient Multicolour Upconversion

Emission in Transparent Colloids of Lanthanide-Doped NaYF4 Nanocrystals. Advanced Materials 2004,

16 (23‐24), 2102-2105. 4.

Lin, M.;

Zhao, Y.;

Wang, S.;

Liu, M.;

Duan, Z.;

Chen, Y.;

Li, F.;

Xu, F.; Lu, T., Recent

advances in synthesis and surface modification of lanthanide-doped upconversion nanoparticles for biomedical applications. Biotechnology Advances 2012, 30 (6), 1551-1561. 5.

Suyver, J. F.;

Aebischer, A.;

Biner, D.;

Gerner, P.;

Grimm, J.;

Heer, S.;

Krämer, K. W.;

Reinhard, C.; Güdel, H. U., Novel materials doped with trivalent lanthanides and transition metal ions showing near-infrared to visible photon upconversion. Optical Materials 2005, 27 (6), 1111-1130. 6.

Evans, J. E.;

Jungjohann, K. L.;

Browning, N. D.; Arslan, I., Controlled Growth of Nanoparticles

from Solution with In Situ Liquid Transmission Electron Microscopy. Nano Letters 2011, 11 (7), 28092813. 7.

Qian, D.; Dickey, E. C., In-situ transmission electron microscopy studies of polymer–carbon

nanotube composite deformation. Journal of Microscopy 2001, 204 (1), 39-45. 8.

McDowell, M. T.; Ryu, I.; Lee, S. W.; Wang, C.; Nix, W. D.; Cui, Y., Studying the Kinetics of

Crystalline Silicon Nanoparticle Lithiation with In Situ Transmission Electron Microscopy. Advanced

12


Page 13 of 14 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


Materials 2012, 24 (45), 6034-6041. 9.

Wang, F.; Wang, X., Mechanisms in the solution growth of free-standing two-dimensional inorganic

nanomaterials. Nanoscale 2014, 6 (12), 6398-6414. 10. Bian, W.;

Lin, Y.;

Wang, T.;

Yu, X.;

Qiu, J.;

Zhou, M.;

Luo, H.;

Yu, S. F.; Xu, X., Direct

Identification of Surface Defects and Their Influence on the Optical Characteristics of Upconversion Nanoparticles. ACS Nano 2018, 12 (4), 3623-3628. 11. Xiang, G.;

Zhang, J.;

Hao, Z.;

Zhang, X.;

Pan, G.-H.;

Chen, L.;

Luo, Y.;

Lü, S.; Zhao,

H., Solvothermal synthesis and upconversion properties of about 10nm orthorhombic LuF3: Yb3+, Er3+ rectangular nanocrystals. Journal of Colloid and Interface Science 2015, 459, 224-229. 12. Chen, G.;

Ohulchanskyy, T. Y.;

Kumar, R.; Ågren, H.; Prasad, P. N., Ultrasmall Monodisperse

NaYF4:Yb3+/Tm3+ Nanocrystals with Enhanced Near-Infrared to Near-Infrared Upconversion Photoluminescence. ACS Nano 2010, 4 (6), 3163-3168. 13. Ma, Y.; Deng, T.;

Gao, W.;

Shan, H.;

Chen, W.;

Shang, W.;

Tao, P.;

Song, C.;

Addiego, C.;

Pan, X.; Wu, J., Platinum-Based Nanowires as Active Catalysts toward Oxygen Reduction

Reaction: In Situ Observation of Surface-Diffusion-Assisted, Solid-State Oriented Attachment.

Advanced Materials 2017, 29 (46), 1703460. 14. Zhou, J.; Wen, S.;

Liao, J.;

Clarke, C.; Tawfik, S. A.; Ren, W.; Mi, C.; Wang, F.; Jin, D.

J. N. P., Activation of the surface dark-layer to enhance upconversion in a thermal field. 2018, 12 (3), 154.

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Abstract Graphic

Figure caption: Growth process of LuF3 nanoflakes, the corresponding TEM images and upconversion emission spectra.

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Growth Processes of LuF3 Upconversion Nanoflakes with the

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