Controlled Synthesis of Uniform NaxScF3+x Nanopolyhedrons

Subscriber access provided by NEW YORK UNIV

Article

Controlled Synthesis of Uniform NaxScF3+x Nanopolyhedrons, Nanoplates, Nanorods and Nanospheres Using Solvents Wenbo Pei, LiLi Wang, Jiansheng Wu, Bo Chen, Wei Wei, Raymond Lau, Ling Huang, and Wei Huang Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b00391 • Publication Date (Web): 05 May 2015 Downloaded from http://pubs.acs.org on May 10, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Crystal Growth & Design is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 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

Crystal Growth & Design

Controlled

Synthesis

Nanopolyhedrons,

of

Uniform

Nanoplates,

NaxScF3+x

Nanorods

and

Nanospheres Using Solvents Wen-Bo Pei,†§ Lili Wang,† Jiansheng Wu,‡ Bo Chen,† Wei Wei,† Raymond Lau,†* Ling Huang,§* Wei Huang§

† School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, 637459, Singapore. § Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM), Jiangsu National Synergistic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University (NanjingTech), 30 South Puzhu Road, Nanjing, 211816, P.R. China. ‡ School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Ave, 639672, Singapore

Tel.: +65 63168830 Fax: +65 67947553 Email: [email protected], [email protected]

ACS Paragon Plus Environment

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

Page 2 of 17

ABSTRACT: NaxScF3+x nanocrystals with controllable shapes were synthesized in the oleic acid/1-octadecene (OA/OD) coprecipitation reaction system. By adjusting the volume ratio of the solvents, well-defined NaxScF3+x nanopolyhedrons, nanoplates, nanorods and nanospheres with different sizes and phases could be selectively obtained. The as-prepared NaxScF3+x nanocrystals were well characterized and investigated. Based on the results obtained, it was found that the solvents influenced significantly the growth process of the NaxScF3+x nanocrystals. A change in the nucleus formation rate and the responsible crystal planes leads to different morphologies of the resulting nanocrystals. Further investigation on the upconversion (UC) luminescence of the Yb/Er co-doped NaxScF3+x nanocrystals showed that, NaxScF3+x nanostructures could serve as host matrices to give strong UC luminescence. In addition, their different phases and morphologies were responsible for the diverse luminescence intensity.


2

Page 3 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


Introduction Lanthanide ion (Ln3+) doped upconversion nanoparticles (LDUNs) have attracted increasing interests in the past decades.1-8 Arising from the abundant and unique 4f inner shell energy levels configurations of Ln3+, LDUNs show superior features including narrow emission band widths, long luminescence lifetime and high resistance to photobleaching, photoblinking and photochemical degradation.9-13 The above-mentioned features coupled with high chemical stability, low toxicity and low autofluorescence background make LDUNs a kind of substitution for conventional luminescent materials such as organic dyes and quantum dots, becoming highly promising optical materials.14, 15 Meanwhile, LDUNs were found to have potential applications in diverse fields such as catalysis, electronics, magnetics and biology.5, 16-20 Suitable applications normally require the LDUNs to be synthesized easily and have precise properties, such as specific morphology, size, crystallographic phase and luminescence property.21-27 Hence, the fundamental research on the controlled synthesis and understanding the nature of nanocrystal growth is of utmost importance. It provides insights for further applications of the nanocrystals in related blooming areas.24, 28-31 Among the literature on LDUNs, NaMF4 (M = Y, La, Gd or Lu) fluorides are one of the most widely studied host UC systems because of their efficient hosts for visible UC luminescence.17, 32-36

Fluorides have intrinsically low phonon energies, leading to a decrease in the non-radiative

relaxation rate and improvement of the UC efficiency.37, 38 However, it is noticed that NaxScF3+x fluorides have rarely been reported in the literatures. Scandium (Sc) is a unique rare earth element and has distinct electron configuration and much smaller ion radius compared with other Ln3+ ions. It is well known that the UC emission characteristic is related to the crystal field and


3


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 4 of 17

the distance between rare-earth ions in the host lattices.39 Therefore, unique optical properties different from other Ln3+-based UC systems can be expected from Sc3+-based UC system. It is encouraging to demonstrate for the first time that Sc3+-based UC system has unique characteristic that give strong emission with a large red to green ratio when co-doped with Yb/Er. Since our first report on the NaxScF3+x host UC system in 2012,40 additional studies on this system were also performed by other research groups.41-42 Chen and co-workers determined for the first time the crystal structure of NaScF4. They also demonstrated its applications as a heterogeneous UC luminescence bioprobe to detect avidin with a detection limit of 180 pM.42 Yang and co-workers reported the color-tunable and enhanced luminescence of well-defined sodium scandium fluoride nanocrystals.43 It is believed that further development of Sc3+-based LDUNs is highly promising, especially the fundamental research on controlled synthesis and understanding the nature of the NaxScF3+x nanocrystals growth process. In this paper, a facile strategy of adjusting the volume ratio of solvents to synthesize welldefined NaxScF3+x nanocrystals with different morphologies and phases was demonstrated. We aim to investigate the influence of solvents on the phase and shape evolution of the as-prepared nanocrystals. A systematic investigation of the UC emission process for the Yb/Er co-doped NaxScF3+x nanocrystals was also conducted. Experimental Section Chemicals and Materials All the starting chemicals and reagents used in the experiments were purchased from SigmaAldrich, which include ScCl3·6H2O (99.99%), YbCl3·6H2O (99.9%), ErCl3·6H2O (99.9%), NaF (99%), oleic acid (OA) (90%) and 1-octadecene (OD) (90%), alcohol (95%), cyclohexane (99.9%). They were used as received without further purification.


4

Page 5 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


Nanocrystals Synthesis A modified coprecipitation method was used for the synthesis of NaxScF3+x:Yb/Er nanocrystals. For a typical procedure, 0.5 mmol RECl3·6H2O (0.39 mmol ScCl3·6H2O, 0.1 mmol YbCl3·6H2O, 0.01 mmol ErCl3·6H2O) were added to a 50 mL flask. A mixture of proper amount of OA and OD with total volume of 25 mL was added to the flask. The solution was heated to 160 oC at argon protection under vigorous magnetic stirring. 1 mmol NaF was added directly at this temperature to the solution and kept stirring at 160 oC for 30 minutes. Thereafter, the solution was heated to 300 oC directly and kept for 1.5 h. Then the resulting solution was cooled down to room temperature and ethanol was added. The as-prepared nanocrystals were collected by centrifugation, washed with water and ethanol for several times, and finally re-dispersed in cyclohexane. Characterizations The morphology and structure of the nanocrystals were characterized by low resolution (JEOL JEM-1400) transmission electron microscopic (TEM) operating at an accelerating voltage of 100 kV. High resolution TEM (HRTEM) images were collected at an accelerating voltage of 200 kV on a JEOL JEM-2010 electron microscope. EDS measurement was collected by using JED-2300 analysis station operating at 20 kV. The crystallographic information of the samples was obtained by using XRD measurements, on a Bruker D2 Phaser X-ray diffractometer with Cu Kα radiation (λ = 1.5406 Å) from 10° to 70° at a step of 0.1°/s. The UC luminescence spectra were recorded on Horiba Jobin Yvon FluoroMax-4 system and an external MDL/MDL-H-980 nm CW laser system was used as the excitation source. Photostability test was recorded on F-4500 FL Spectrophotometer for 30 mins continuous laser irradiation. The nanocrystals were dispersed in


5


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 6 of 17

cyclohexane (1 wt%) in a standard quartz cuvette at room temperature to measure the photoluminescence spectra. Results and Discussion Morphologies and phases of NaxScF3+x:Yb/Er nanocrystals Solvent is commonly believed to play an important role in the formation of nanocrystals. Four typical OA:OD volume ratios of 1:4, 3:7, 1:1 and 7:3 with a total volume of 25 mL were selected to illustrate the details of the solvent effects on the NaxScF3+x:Yb/Er nanocrystals evolution. With the OA:OD volume ratio changing from 1:4 to 7:3, the amount of OA, the capping ligand as well as the polar surfactant solvent, increases gradually. All the other experimental parameters, such as the amount of chemicals, reaction temperature, reaction time and experimental procedure, were kept constant in order to eliminate the contribution from other potential parameters. EDS results shown in Figure S1 indicate that the as-prepared nanocrystals are mainly composed of Na, Sc, F, Yb and a small amount of Er element. It confirms the successful synthesis of the NaxScF3+x:Yb/Er nanocrystals. TEM images shown in Figure 1 indicate that, very uniform nanocrystals with dramatically different morphologies and sizes can be obtained at different solvent conditions. The low magnification images (a-d) demonstrate the uniform nanocrystals with good monodispersity. The high magnification images (e-h) give more details of the particular morphology of each nanocrystals. Fine nanopolyhedrons with mean size of 53.4 nm (a and e) can be synthesized at the lowest OA:OD volume ratio of 1:4. When OA:OD volume ratio was increased to 3:7, rectangular nanoplates could be acquired and their size was increased to 162.3 nm in length and 28.3 nm in diameter (b and f). In addition, it is noticed that the anisotropic rectangular nanoplates favor ‘side-to-side’ pattern along the long-axis direction on the substrate. Such pattern allows the


6

Page 7 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


minimal Gibbs free energy of the arrangement of OA molecules that attached on the surface of the nanocrystals under the current nonpolar dispersing solvent condition.30 When OA:OD volume ratio reached 1:1, the nanocrystals increased in size and highly uniform nanorods were obtained with mean size of 190.2 nm in length and 38.9 nm in diameter (c and g). Such uniform nanorods are rarely seen in the majority of the previous studies on Y3+/Ln3+-based nanomaterials. As OA became the dominant component of the solvents at OA:OD volume ratio of 7:3, the resulting nanocrystals changed dramatically to small nanospheres with mean size of 33.1 nm (d and h). The results indicated that the as-prepared NaxScF3+x:Yb/Er nanocrystals with different morphologies and sizes can be selectively synthesized by simply adjusting the OA:OD volume ratio.

Figure 1. TEM images of the NaxScF3+x:Yb/Er nanocrystals synthesized at different OA:OD volume ratio of 1:4 (a, e); 3:7 (b, f); 1:1 (c, g) and 7:3 (d, h).

XRD patterns were collected for the crystallographic phase confirmation of the resulting nanocrystals, which is helpful to understand the nanocrystals evolution. It can be seen from Figure 2 that all the peaks in the three XRD patterns (a, b and c) can be clearly indexed to the standard JCPDS card of monoclinic Na3ScF6 (JCPDS 20-1153) phase. No peaks from impurities


7


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 8 of 17

are observed. It indicates that these Na3ScF6 nanocrystals synthesized at OA:OD volume ratios of 1:4, 3:7 and 1:1 are of high purities and crystallinities. Moreover, pure hexagonal NaScF4 (JCPDS 20-1152) phase can be confirmed for nanocrystals synthesize at OA:OD volume ratio of 7:3 (d). The broadening feature of the diffraction peaks distinctly reveals the nanocrystalline nature of the samples. However, it is to note that the peak width for the nanorods samples (c) shows abnormal broadening. Such phenomenon suggests that the nanorods may be formed from aggregation and growth of small particles. HRTEM image for the nanorod in Figure S2 shows that the crystal lattice is not maintained. Fractures and flaws can be found on the surface of the nanorods, which give indirect evidence of the same conclusion. Similar phenomenon was also found in NaYF4 hexagonal prisms, which are comprised of small nanoparticles.22

Figure 2. XRD patterns of the as-prepared NaxScF3+x:Yb/Er nanocrystals synthesized at OA:OD volume ratio of 1:4 (a), 3:7 (b), 1:1 (c) and 7:3 (d). Red and black lines at the top and bottom are


8

Page 9 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


the standard XRD patterns of hexagonal phase NaScF4 crystals (JCPDS card No. 20-1152) and monoclinic phase Na3ScF6 crystals (JCPDS card No. 20-1153).

The above results indicate that the presence of low fraction of OA in the mixed solvents reaction system favors monoclinic Na3ScF6 phase. Once OA is excessive, hexagonal NaScF4 phase is formed. In order to confirm the interpretation, NaxScF3+x nanocrystals synthesized at OA:OD volume ratio of 2:3 and 3:2 were obtained for comparison. The corresponding XRD patterns are shown in Figure S3. The one synthesized at OA:OD volume ratio of 2:3 could be indexed to the monoclinic Na3ScF6 phase. The latter one shows the mixture phases of both monoclinic Na3ScF6 and hexagonal NaScF4 phases. In fact, solvent condition with OA:OD volume ratio of 4:1 was also applied but no visible nanocrystals could be collected. When the resulting NaxScF3+x:Yb/Er solution was exposed to the laser irradiation, weak emission could still be observed. It indicates the formation of extra small nanocrystalline core, which are hard to be collected by centrifugation but still able to show weak UC emissions. The results demonstrate clearly that the solvents, especially OA plays a critical role on the nanocrystals evolution. When the amount of OA is equal or less than OD, the reaction is a thermodynamically determined process, and the corresponding thermodynamically stable monoclinic Na3ScF6 phase is formed.44 The size and morphology of the resulting nanocrystals is dependent on the dynamic process. A low OA content increases the nucleation speed and leads to the formation of the small sized nanocrystals with isotropic characteristic. Otherwise, large anisotropic nanocrystals can be obtained. This explains the observation of having the nanorods to be the biggest size, and nanopolyhedrons to be the smallest size within the monoclinic Na3ScF6 nanocrystals. Moreover, an increase in the amount of OA reduces the rate of nucleation and nanocrystal growth that is favorable for the metastable hexagonal NaScF4 phase. When OA becomes the dominant


9


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 10 of 17

composite, pure NaScF4 with small size is formed. However, if the amount of OA is as much as 4 times of OD, only extra small nanocrystalline core can be formed. As the nanocrystals grow, competition between F- ions and rare earth oleate complex is restrained because of an excess amount of OA attached on the surfaces of the as-formed nanocrystalline core. Further growth of the nanocrystals at that solvent condition becomes impossible. Table 1 summarizes the experimental conditions, the corresponding morphologies and sizes, as well as the crystallographic phases of the resulting NaxScF3+x:Yb/Er nanocrystals. Shape-control mechanism of Na3ScF6:Yb/Er nanocrystals It is important to explore the morphology evolution process of the monoclinic Na3ScF6 phase with a change in the OA:OD volume ratio. It is known that the final shape of a nanocrystal is determined by the growing competition of different crystal planes under the given synthetic condition. In the OA/OD coprecipitation reaction system, the growth of the as-prepared nanocrystals is started with the reaction between F- ions and rare earth oleate complex.28 As the reaction proceeded, small particles formed can aggregate with each other to form bigger particles. Under the driving forces of free energy, thermal treatment and crystal lattice energy, the oleic attached on the particle surface were removed and the aggregated particles can merged to form single crystals generally. OA acts as both the polar surfactant solvent and capping ligand, which can arrest the growth of the nanoparticles and limits particle size. With different amount of OA in the reaction system, a change in the nucleus formation rate and the responsible crystal planes was present. A reduction in OA allows an increase in the nucleation rate, leading to an increase in the number of nucleation and hence more small sized nanocrystals with good crystallinity. On the other hand, an increase in OA in the system reduces the rate of nucleation and nanocrystals growth which may cause the formation of polycrystalline particles. HRTEM


10

Page 11 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


images for the single nanocrystals of nanopolyhedrons, nanoplates as well as polycrystalline nanorods shown in Figure S4 and S2 can support this interpretation to some extent. With the nucleation formation and nanocrystals growth, the adsorption effect of OA on different crystal planes is also different. The adsorption effect can further influence the chemical potential and the growth rate of the responsible crystal planes. Furthermore, NaF is far from insufficient compared with Ln3+ in our synthetic route (Ln3+:NaF = 1:2). Crystal growth takes precedence at particular crystalline planes happening. Last but not least, particle size has its own effect on the final shape, i.e., small particles prefer isotropic to anisotropic because of the increase in surface energy with decreasing particle size. Under the synergistic effect of these factors, the Na3ScF6 nanocrystals show the fastest nucleation formation rate and lead to the smallest particle size with isotropic characteristic at the lowest OA content (OA:OD = 1:4). On the contrary, the largest anisotropic nanorods were obtained at OA:OD volume ratio of 1:1. Different morphologies of the resulting Na3ScF6 nanocrystals are realized (scheme 1).

Scheme 1. Schematic illustration of the nanocrystal shape evolution at varying reaction solvents medium.


11


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 12 of 17

Upconversion emission characteristics of the different shaped nanocrystals To explore the capability of the NaxScF3+x nanostructures to serve as host matrices for UC properties, luminescence spectra were collected under 980 nm laser excitation for the resulting Yb/Er co-doped nanocrystals. On the basis of the emission spectra shown in Figure 3, three characteristic peaks of the doping Er3+ ions located at around 408 nm, 541 nm and 654 nm can be found for all the samples. The emissions can be ascribed to 2H9/2 → 4I15/2 transition; 2H11/2 → 4

I15/2 and 4S3/2 → 4I15/2 transitions as well as 4F9/2 → 4I15/2 transition respectively (Figure S4).45, 46

Moreover, it is found that the hexagonal phase NaScF4:Yb/Er nanospheres show obviously stronger UC luminescence than the monoclinic Na3ScF6:Yb/Er ones. This agrees well with our previously reported results.40 Due to the multiple independent sites exist for both Yb3+ and Er3+ in NaScF4, that increase the number of possible Yb3+ to Er3+ energy transfer processes. For the monoclinic Na3ScF6:Yb/Er nanoscrystals, the nanorods give the strongest UC luminescence, while the nanoplates give the weakest luminescence, and the nanopolyhedrons fall in the middle. The findings are reasonable. The nanorods have larger size than the other two, implying more active ions deeply inside being as luminescent centre. For the nanoplates, though the size is larger than those of the nanopolyhedrons, their high aspect ratio (particularly the thin thickness) enable a high surface area for many doped Er3+ ions to be exposed on the surface. Thus the exposed Er3+ ions cannot function as luminescent centers as those doped deep inside. In other words, the nanoplates have much more surface defects, which significantly reduced the fluorescence to a point even weaker than the smaller but with good crystalline nanopolyhedrons.


12

Page 13 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


Figure 3. UC luminescence spectra of the corresponding NaxScF3+x:Yb/Er nanocrystals.

Furthermore, the luminescence intensity dependence of the excitation power for NaScF4:Yb/Er nanocrystals was investigated to understand the number of photons involved in the UC process in detail. It is well known that the integrated UC luminescence intensity If is proportional to Pn, where P is the pumping laser power, and n is the number of laser photons required in populating the upper emitting state. Figure 4 shows the typical plot of pump-power dependence of UC luminescence. It can be found that the value of n is 2.84, 1.93, 1.95 and 1.94 for the corresponding 2H9/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 as well as 4F9/2 → 4I15/2 transitions of Er3+ ion. The results suggest that the transitions are of three-, two-, two- and twophoton UC processes respectively, which are coincident with the analysis of UC energy transfer mechanism shown in Figure S5. In addition, neither photobleaching nor blinking were found for the as-prepared nanoparticles over 30 min continuous laser excitation (Figure S6), demonstrating the good photostability.


13


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 14 of 17

Figure 4. In-In plots of the UC emission intensity versus NIR excitation power for the 2H9/2 → 4

I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2 transition of Er3+ ions.

Conclusions In summary, a facile route to synthesize NaxScF3+x nanocrystals with controllable shapes was demonstrated. The well-defined NaxScF3+x nanopolyhedrons, nanoplates, nanorods and nanospheres with different sizes and phases can be selectively obtained in the OA/OD coprecipitation reaction system through the adjustment of the OA:OD volume ratio. The influence of solvents, especially OA on the phase and shape evolution of the as-prepared nanocrystals was studied in detail. Based on the results obtained, the mechanism for the crystal evolution process is discussed. Furthermore, the different UC emission properties for these different shaped Yb/Er co-doped NaxScF3+x nanocrystals are investigated and the UC energy transfer mechanism is proposed.

Acknowledgements


14

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


R. L. thanks the financial support from NEA ETRP Grant (Ref No.: 1102 108). L. H. is grateful for the financial support from the National Natural Science Foundation of China (Grant: 21379105). It is also supported by China Postdoctoral Science Foundation (grant No: 2013M541655) and Natural Science Foundation of Jiangsu Province, China (grant No: BK20131404, 13KJB150016).

Supporting Information. EDS data, HRTEM images, XRD patterns, UC energy transfer mechanism and photostability for the resulting NaxScF3+x:Yb/Er nanocrystals. This material is available free of charge via the Internet at http://pubs.acs.org.

Corresponding Author * E-mail: [email protected], Tel.: +65 63168830, fax: +65 67947553 for Prof. Lau; E-mail: [email protected], Tel.: +86 25 83587980 for Prof. Huang.

Notes The authors declare no competing financial interest.

REFERENCES 1. 2. 3. 4. 5. 6. 201-212. 7. 8. 9. 10. 11.

Haase, M.; Schäfer, H. Angew. Chem. Int. Ed. 2011, 50, 5808-5829. Wang, G.; Peng, Q.; Li, Y. Acc. Chem. Res. 2011, 44, 322-332. Zhang, Y.; Zhang, L.; Deng, R.; Tian, J.; Zong, Y.; Jin, D.; Liu, X. J. Am. Chem. Soc. 2014, 136, 4893-4896. Gai, S.; Li, C.; Yang, P.; Lin, J. Chem. Rev. 2014, 114, 2343-2389. Zhou, J.; Liu, Z.; Li, F. Chem. Soc. Rev. 2012, 41, 1323-1349. Wang, X.; Chang, H.; Xie, J.; Zhao, B.; Liu, B.; Xu, S.; Pei, W.; Ren, N.; Huang, L.; Huang, W. Coord. Chem. Rev. 2014, 273–274, Wang, F.; Deng, R.; Wang, J.; Wang, Q.; Han, Y.; Zhu, H.; Chen, X.; Liu, X. Nat Mater 2011, 10, 968-973. Wang, Y.-F.; Liu, G.-Y.; Sun, L.-D.; Xiao, J.-W.; Zhou, J.-C.; Yan, C.-H. ACS nano 2013, 7, 7200-7206. Cheng, L.; Wang, C.; Liu, Z. Nanoscale 2013, 5, 23-37. Li, L.-L.; Wu, P.; Hwang, K.; Lu, Y. J. Am. Chem. Soc. 2013, 135, 2411-2414. Schietinger, S.; Aichele, T.; Wang, H.-Q.; Nann, T.; Benson, O. Nano Lett. 2009, 10, 134-138.


15


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 16 of 17

12. Qiao, X.-F.; Zhou, J.-C.; Xiao, J.-W.; Wang, Y.-F.; Sun, L.-D.; Yan, C.-H. Nanoscale 2012, 4, 4611-4623. 13. Li, L.-L.; Zhang, R.; Yin, L.; Zheng, K.; Qin, W.; Selvin, P. R.; Lu, Y. Angew. Chem. Int. Ed. 2012, 51, 6121-6125. 14. Wu, J.; Tian, Q.; Hu, H.; Xia, Q.; Zou, Y.; Li, F.; Yi, T.; Huang, C. Chem. Commun. 2009, 4100-4102. 15. Gorris, H. H.; Wolfbeis, O. S. Angew. Chem. Int. Ed. 2013, 52, 3584-3600. 16. Wang, F.; Liu, X. Chem. Soc. Rev. 2009, 38, 976-989. 17. Liu, Y.; Tu, D.; Zhu, H.; Chen, X. Chem. Soc. Rev. 2013, 42, 6924-6958. 18. Yang, Y.; Liu, F.; Liu, X.; Xing, B. Nanoscale 2013, 5, 231-238. 19. Zhou, J.; Deng, J.; Zhu, H.; Chen, X.; Teng, Y.; Jia, H.; Xu, S.; Qiu, J. J. Mater. Chem. C 2013, 1, 8023-8027. 20. Li, K.; Fan, J.; Mi, X.; Zhang, Y.; Lian, H.; Shang, M.; Lin, J. Inorg. Chem. 2014, 53, 12141-12150. 21. Yan, Z.-G.; Yan, C.-H. J. Mater. Chem. 2008, 18, 5046-5059. 22. Liang, X.; Wang, X.; Zhuang, J.; Peng, Q.; Li, Y. Adv. Funct. Mater. 2007, 17, 2757-2765. 23. Bogdan, N.; Vetrone, F.; Ozin, G. A.; Capobianco, J. A. Nano Lett. 2011, 11, 835-840. 24. Li, C.; Lin, J. J. Mater. Chem. 2010, 20, 6831-6847. 25. Tian, G.; Gu, Z.; Zhou, L.; Yin, W.; Liu, X.; Yan, L.; Jin, S.; Ren, W.; Xing, G.; Li, S.; Zhao, Y. Adv. Mater. 2012, 24, 1226-1231. 26. Zhou, J.; Zhu, X.; Chen, M.; Sun, Y.; Li, F. Biomaterials 2012, 33, 6201-6210. 27. Zhang, Y.; Wu, Z.; Geng, D.; Kang, X.; Shang, M.; Li, X.; Lian, H.; Cheng, Z.; Lin, J. Adv. Funct. Mater. 2014, 24, 6581-6593. 28. Ding, Y.; Teng, X.; Zhu, H.; Wang, L.; Pei, W.; Zhu, J.-J.; Huang, L.; Huang, W. Nanoscale 2013, 5, 11928-11932. 29. Qiu, H.; Chen, G.; Sun, L.; Hao, S.; Han, G.; Yang, C. J. Mater. Chem. 2011, 21, 17202-17208. 30. Boyer, J.-C.; Gagnon, J.; Cuccia, L. A.; Capobianco, J. A. Chem. Mater. 2007, 19, 3358-3360. 31. Bao, L.; Li, C.; Tao, Q.; Xie, J.; Mei, Y.; Xiong, Y. Nanotechnology 2013, 24, 145604. 32. Wang, F.; Liu, X. Acc. Chem. Res. 2014. 33. Chen, F.; Bu, W.; Zhang, S.; Liu, J.; Fan, W.; Zhou, L.; Peng, W.; Shi, J. Adv. Funct. Mater. 2013, 23, 298-307. 34. Heer, S.; Kömpe, K.; Güdel, H. U.; Haase, M. Adv. Mater. 2004, 16, 2102-2105. 35. Sivakumar, S.; van Veggel, F. C. J. M.; Raudsepp, M. J. Am. Chem. Soc. 2005, 127, 12464-12465. 36. Na, H.; Jeong, J.; Chang, H.; Kim, H.; Woo, K.; Lim, K.; Mkhoyan, K. A.; Jang, H. Nanoscale 2014, 6, 7461-8. 37. Deng, R.; Xie, X.; Vendrell, M.; Chang, Y.-T.; Liu, X. J. Am. Chem. Soc. 2011, 133, 20168-20171. 38. Xie, X.; Gao, N.; Deng, R.; Sun, Q.; Xu, Q.-H.; Liu, X. J. Am. Chem. Soc. 2013, 135, 12608-12611. 39. Auzel, F. Chem. Rev. 2003, 104, 139-174. 40. Teng, X.; Zhu, Y.; Wei, W.; Wang, S.; Huang, J.; Naccache, R.; Hu, W.; Tok, A. I. Y.; Han, Y.; Zhang, Q.; Fan, Q.; Huang, W.; Capobianco, J. A.; Huang, L. J. Am. Chem. Soc. 2012, 134, 8340-8343. 41. Pang, M.; Feng, J.; Song, S.; Wang, Z.; Zhang, H. CrystEngComm 2013, 15, 6901-6904. 42. Ai, Y.; Tu, D.; Zheng, W.; Liu, Y.; Kong, J.; Hu, P.; Chen, Z.; Huang, M.; Chen, X. Nanoscale 2013, 5, 6430-6438. 43. Fu, H.; Yang, G.; Gai, S.; Niu, N.; He, F.; Xu, J.; Yang, P. Dalton Transactions 2013, 42, 7863-7870. 44. Pei, W.-B.; Chen, B.; Wang, L.; Wu, J.; Teng, X.; Lau, R.; Huang, L.; Huang, W. Nanoscale 2015, 7, 4048-4054. 45. Wang, L.; Chen, H.; Zhang, D.; Zhao, D.; Qin, W. Mater. Lett. 2011, 65, 504-506. 46. Wang, L.; Xue, X.; Shi, F.; Zhao, D.; Zhang, D.; Zheng, K.; Wang, G.; He, C.; Kim, R.; Qin, W. Opt. Lett. 2009, 34, 2781-2783.

Table 1. Experimental conditions, the corresponding morphologies and sizes, as well as the crystallographic phases of the resulting NaxScF3+x:Yb/Er nanocrystals. OA:OD 1:4 3:7 2:3 1:1 3:2 7:3

Shape polyhedron nanoplate not regular nanorod not regular nanosphere

Size ( length × diameter) / nm 53.4 ± 1.0 (162.3 ±5.5) × (28.3 ± 1.2) (190.2 ± 7.4) × (38.9 ± 1.1) 33.1 ± 0.9

Crystallographic phase Monoclinic Na3ScF6 Monoclinic Na3ScF6 Monoclinic Na3ScF6 Monoclinic Na3ScF6 Mixture of both phases Hexagonal NaScF4


16

Page 17 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


For Table of Contents Use Only

Controlled Synthesis of Uniform NaxScF3+x Nanopolyhedrons, Nanoplates, Nanorods and Nanospheres Using Solvents Wen-Bo Pei,†§ Lili Wang,† Jiansheng Wu,‡ Bo Chen,† Wei Wei,† Raymond Lau,†* Ling Huang,§* Wei Huang§

Simultaneous control over the shape, size, as well as crystallographic phase of the NaxScF3+x:Yb/Er nanocrystals was successfully achieved simply by the adjustment of OA/OD volume ratio.


17

Controlled Synthesis of Uniform NaxScF3+x Nanopolyhedrons

Recommend Documents