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Near-Infrared Upconversion Transparent Inorganic Nanofilm: ConfinedSpace Directed Oriented Crystal Growth and Distinctive Ultraviolet Emission Xiaoxia Liu, Yaru Ni, Cheng Zhu, Liang Fang, Song Hu, Zhitao Kang, Chunhua Lu, and Zhongzi Xu Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b00874 • Publication Date (Web): 13 Sep 2016 Downloaded from http://pubs.acs.org on September 18, 2016

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Crystal Growth & Design

Near-Infrared Upconversion Transparent Inorganic Nanofilm: Confined-Space Directed Oriented Crystal Growth and Distinctive Ultraviolet Emission Xiaoxia Liu,†,§,┴ Yaru Ni,*,†,§, ┴,ǁ Cheng Zhu, †,§, ┴ Liang Fang,†,§, ┴ Song Hu, †,§, ┴ Zhitao Kang,‡ Chunhua Lu,*,†,§, ┴ and Zhongzi Xu†,§, ┴ †

State Key Laboratory of Materials-Orient Chemical Engineering, College of Materials Science

and Engineering, Nanjing Tech University, Nanjing 210096, P. R. China. §

Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing

Tech University, Nanjing 210009, P. R. China. ┴

The synergetic innovation center for advanced material, Nanjing Tech University, Nanjing

210009, PR China. ǁ

Key Laboratory of MEMS of Ministry of Education, Southeast University, Nanjing 210009, P.

R. China. ‡

Electro-Optical Systems Laboratory, Georgia Tech Research Institute, Georgia Institute of

Technology, Atlanta, GA 30332, United States.

ACS Paragon Plus Environment

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ABSTRACT: A well-designed efficient one-step assembly strategy is implemented in this work by constructing a confined nanospace to manufacture an about 120 nm thick inorganic UC nanofilm with highly (101) oriented and morphology-controllable crystal grains, as well as transparent and robust characteristics. The morphology and distribution density of crystal grains of the film can be tuned by varying space heights and precursor concentrations. The confined space incubates a stable growing environment for crystal grains to decrease crystal defects and grow bigger. Therefore, there are high populations of doped Tm ions and high efficiencies of radiation transitions to realize multi-photons ultraviolet (UV) (monitoring range: 300-400 nm) emissions under laser excitation with wide power range. Quantum yields (QYs) of the film in UV region are 4.7 and 16.1 times higher than those of UC nanoparticles (UCNPs) synthesized by the typical thermal decomposition method and hydrothermal method, respectively. The UVenhanced UC film is demonstrated to have the ability to serve as a medium to realize nearinfrared (NIR) induced undersurface photochemical reaction, which may inspire broad applications, such as the UC 3D printing. KEYWORDS: confined-space, upconversion, film, ultraviolet, oriented, photochemical Introduction Upconversion (UC), a distinct anti-Stokes process, with unique properties, has gained lots of reputation and popularity among researchers for the wide range of potential applications in display, anti-counterfeiting, solid-state laser, photovoltaic devices and so on1-7. The desire to fabricate functional composite UC materials with excellent photoluminescence (PL) performances has therefore become a major interest to promote the application3,

8-13

which

demands the transparent and robust characteristics. By far, many strategies require two steps such as UC sol-gel thin films14 and UC nanoparticles (UCNPs) composited functional polymer3,


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8, 15

. The former causes worry about weak adhesion. The latter is frequently-applied but sacrifices

fluorescence intensity because of the necessary small usage and small size normally smaller than 100 nm of UCNPs to reduce the light scattering16, 17. Besides, the absorption of organic groups on photons with specific wavelength can lead to the consumption of UC fluorescence. In recent years, self-assembly films with UCNPs have been reported and attracted many researchers’ interest

15, 16

. However, the hard to be extended assembly area and weak adhesion have limited

their further development. One-step synthesis of UC films is also reported such as by pulsed laser deposition18 and molecular beam epitaxy19, which however demand expensive devices. UC films prepared by electrodeposition20-22 are popular and can alleviate these problems, but still have some drawbacks such as selective ITO substrates and unreachable UC fluorescence until prior annealing at a high temperature18, 22. Therefore, to further improve properties of composite UC films and explore their novel and intrinsic functions, it is necessary to develop a new and simple one-step preparation approach to meet demands of at least inexpensive, robust, available fluorescence and additionally transparent, controllable growth. In our work, an easily constructed confined space between superimposed silica glass substrates which only demand cleaning with ethanol is utilized to fabricate a composite inorganic UC nanofilm characteristic as transparent, robust, oriented, and controllable of morphology based on hydrothermal reaction. Besides, the crystal grain size of the as-prepared space-confined film is micro/nano scale, which means the available high transmittance does not need to sacrifice the UC fluorescence. On the contrary, the large size brings about the high crystallinity to contribute to strong photoluminescence. The confined space plays an important role to influence the formation and properties of the film. The environment for the growth of the space-confined synthetic film is totally different from traditional ones due to the limited growth space. Therefore,


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the inhaling of precursors into the space is really important and has a great effect on the crystal grain density of the film, which is discussed in the paper. In the following growth process of the film, the confined space plays an indispensable role to limit the fluid flow. The impact of fluid flow on atoms is decreased, which makes adatoms not easy to be washed away. Therefore crystal grain of the film tends to grow bigger and is approximately 3 times larger than hydrothermal UCNPs counterparts. Besides, adatoms are energetic to jump into existing defect sites due to the stable growing environment, which thus reduces crystal defects. The two surprise windfalls promote populations of doped Tm ions, particularly of 3P2, 1I6 and 1D2 energy levels, and make the film possess enhanced overall fluorescence intensity and especially multiphoton ultraviolet (UV) emissions. The relative quantum yield (RQY) is introduced in the work to assess the UC efficiency of the space-confined film because the measurement inaccuracy of the absolute QY which is normally measured with a commercial fluorometer and an integrating sphere23 is still large because the excitation power is required to be much stronger than the emission one and consequently the test system is often not the first choice of most reports24. The QYs of typical hexagonal NaYF4:20%Yb,2%Er UCNPs with the size ranging from 10 to 100 nm are measured at a radiation power density of 20 W/cm2 to be in the range of 0.005% to 0.3%23. QYs of UCNPs are normally low because of a mass of quenching centers and the larger size of crystal grain makes the higher QY. Compared with UCNPs counterparts with the same stoichiometric ratio synthesized by thermal decomposition method and hydrothermal method, QYs in 300-850 nm of the space-confined film are 3.4 and 15.4 times higher and QYs in 300-400 nm are 4.7 and 16.1 times higher, respectively. Furthermore, in comparison with the PDMS composite UC film


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which is widely researched, the space-confined film is found to have 32.6 times enhanced overall (300-850 nm) fluorescence and 67.1 times enhanced UV (300-400 nm) fluorescence. The UV-enhanced UC film is demonstrated to be able to serve as a medium to realize NIRinduced undersurface photochemical reaction for the novel optical switches and data memory devices24. The emitted sightless UV photons contribute to the polymerization of oligomers with the assistance of photoinitiator and the visible blue emissions serve as the indicator lights. Complex patterns are able to be painted with the NIR laser “pen” on the film. This may inspire broad applications of UC materials, such as the preparation of UC 3D printing. Experimental Materials and Methods Materials. YCl3·6H2O (99.99%), YbCl3·6H2O (99.99%), and TmCl3·6H2O (99.95%) were provided by Beijing Founde Star Science & Technology Co., Ltd.. Sodium oleate (NaOA, 98.0%), Oleic acid (OA, 90%), 1-octadecene (ODE, 90%), and Ethylene glycol dimethacrylate (EDMA, 98%) were bought from Aladin. NaOH (96%) was purchased from Xilong Chemical Co., Ltd.. Sodium citrate (Na3Cit, 99.0%), xylene (99.0%) and methyl methacrylate (MMA, 98%) were obtained from Shanghai Lingfeng Chemical Reagent Co., Ltd.. Sodium fluoride (NaF, 98.0%), NH4F (98%), ethanol (99.7%) and methanol (99.5%) were all purchased from Sinopharm Chemical Reagent Co., Ltd.. Acrylate modified oligomer was purchased from Zhongshan Ketian Electronic Materials Co., Ltd.. 2-Hydroxy-2-methylpropiophenone (1173, 96%) was obtained from TCI. 2,2'-Azo-bis-iso-butyronitrile (AIBN, CP) was bought from Shanghai Shisi Hewei Chemical Co., Ltd.. All the chemicals mentioned above are used as received without further purification.


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Synthesis of hydrothermal precursor solution of NaYF4:Yb,Tm. In a typical hydrothermal synthesis of NaYF4: 20%Yb3+, 0.5%Tm3+ UC precursor, 2 mmol hexahydrate rare earth (RE) chloride including 1.59 mmol YCl3·6H2O, 0.40 mmol YbCl3·6H2O, and 0.01 mmol TmCl3·6H2O were firstly dissolved in 10 mL of distilled water to form the rare earth chloride solution. 2 mmol NaOA and 50 mmol NaF were dissolved in 20 ml and 30 ml of distilled water with magnetic stirring, respectively. The rare earth chloride solution was then added dropwise into NaOA solution along with vigorous stirring for 40 min to form the RE-oleate complex. NaF solution was then added and the mixture was stirred for another 30 min to form the precursor solution. Space-confined growth of NaYF4:Yb,Tm films. In a hydrothermal synthesis of spaceconfined β-NaYF4: 20%Yb3+, 0.5%Tm3+ UC film, standard 1.35 × 1.35 × 1 mm3 silica glasses were ultrasonic cleaned with ethanol repeatedly. 3 superimposed silica glass substrates (labelled as Us, Ms, and Ds up to down, respectively) were placed on the bottom of a PPL vessel and fixed with a customized Teflon support. Precursor solution was transferred into the PPL vessel, which was then sealed in a stainless steel autoclave. Films grow in the confined space constructed between superimposed silica glasses at 220 °C for 24 h. After the autoclave was cooled to room temperature naturally, the composite films were ultrasonic cleaned with distilled water and ethanol for 4 times and dried at 60 °C. The precipitates inside the vessel were collected by centrifugation and washed with distilled water and ethanol for 4 times and then dried at 60 °C for 12 h. NIR-induced synthesis of acrylate modified polymer. A certain amount of acrylate modified oligomer was dispersed in MMA and small amount of photoinitiator 1173 was then added. The mixture was stirred for a while to form a homogeneous solution. The


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solution was then transferred into a customized Teflon vessel. The as-prepared composite UC film was placed into the solution. The 980 nm laser was utilized as the light source illuminating the film to emit UV photons to realize the photochemical reaction. Characterization Crystal structure of UC film was characterized on X-ray diffraction (XRD, SmartLab-9KW, Rigaku) with the constant incident angle of 0.5° at a scanning rate of 5°/min in the 2θ range from 10° to 80° and crystal structure of powders was performed on X-ray diffraction (XRD, SmartLab-3KW, Rigaku) at a scanning rate of 20°/min in the 2θ range from 10° to 80° with Cu Kα radiation (λ = 0.15406 nm). The luminescence spectra were recorded with a fluorescence spectrophotometer (Jobin Yvon FL3-221, HORIBA) equipped with a power-adjustable 980 nm laser (K98SA3M-54W, China) as the excitation source. A pulsed 980 nm laser was used as the excitation source for temporal investigations. The morphology of UC film was acquired from a field emission scanning electron microscope (FESEM, JSM-7600F, JEOL). The cross section images of polymer sheets were obtained from a scanning electron microscope (SEM, JSM6360LV, JEOL). Optical transmittance spectra of UC film was obtained by UV-VIS-NIR scanning spectrophotometer (UV3101PC, Shimadzu). Refractive indexes of silica glass and UC film were measured with Abbe refractometer (WYA-2D). The FT-IR spectra were performed on a Perkin-Elmer FT-IR/FIR Spectrophotometer. Micro-structure of a silica glass surface was observed with an atomic force microscopy (AFM, Dimension Icon, Bruker) at ambient conditions (air, room temperature). Transmission electron microscopy (TEM) of UC film was obtained with JEOL JEM-2100. The substrate was polished till with the thickness of about 50 µm. Composite film was then treated with Ar ion beam cutting. The degree α of Ar ion beams


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was set as 7° to remove the lower glass and then set as 4° to smooth the glass. TEM images can be obtained in the selected thin area as shown in Schematic S1. Results and Discussion Confined spaces can be constructed by superimposing three silica glass substrates with nanoscale surface roughness (Schematic S2, Figure S1, the three superimposed substrates are labelled as Us, Ms, and Ds, up to down). UC films can grow on every substrate (Figure 1, S2 and S3, the three UC composite films up to down are labelled as Uf, Mf, and Df, respectively). The objective substrate Ms is located between the two constructed confined spaces and the space-confined synthetic composite nanofilm Mf with double films is endowed with both unique morphology and outstanding performance and is studied in the work (unless otherwise stated, the film mentioned below means Mf). The space-confined growth of UC inorganic films can be applied to NaYF4, NaLuF4 and NaGdF4 hosts (Figure 1 and S4). Formation mechanism and intrinsic properties of space-confined film are demonstrated with NaYF4 host in the following sections, which is widely researched and has acknowledged remarkable UC fluorescence properties25-27 and doped with 20% Yb3+ ions and 0.5% Tm3+ ions. Since UC fluorescence properties are very dependent on the morphology, the surface ligand sodium oleate (NaOA) which can control the morphology is adjusted and an excellent fluorescence property can be obtained when the molar ratio of NaOA and RE is 1 with the corresponding ribbon-like crystal grain (Figure S5). The UC film is able to complete its growth in the confined space as shown in Figure 1. Firstly, abundant as-prepared precursors composed of REOA3, Na-, F-, Cl- ions along with tiny cubic NaYF4 seeds (Figure S6 and S7) are inhaled into the confined space under the driven of capillary force when heating up. Precursors from all directions into the space will encounter with each


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other or the substrate and then well assemble. Assembled aggregates react to merge and form abundant cubic NaYF4 crystal nucleus as temperature and time increase. Nucleus will grow and transform to hexagonal grains28 and then turn bigger (Figure S8) to form the smooth nanofilm with the thickness of about 120 nm, which has high transmittance (Figure 1b, d).

Figure 1 (a) Schematic diagram of the formation mechanism of space-confined growth of UC film. Step 1: abundant precursors are inhaled into the confined space under the drive of capillary force when heating up. Step 2: precursors in the confined space collide with each other or substrate and combine to form aggregations. Step 3: the nucleation and further grow of crystal grains occur under reaction condition (b) FESEM image of cross section of space-confined synthetic UC films. (c) Schematic diagram of the bonding mechanism of space-confined film with the silica glass substrate (ligand serves as the link to connect the substrate and film) to form the robust film. (d) Transmittance spectra of a composite UC film and a silica glass with an inserted digital photo of the film.


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Furthermore, the film is robust for the still strong fluorescence even after ultrasonic cleaning for 12 h (Figure S10) and ligand NaOA plays an indispensable role to connect the inorganic UC film with the silica glass substrate due to additive reaction. It can be inferred from Figure S9 that RE atoms and carboxylate radicals are not able to be directly bonded with the substrate. Because when surfactants are not utilized or replaced by Na3Cit (which has four binding sites, including three COO− and one hydroxyl group, among which three sites are bonded with RE3+ ion with one unassociated COO−29) in the formation of the UC film, there are both almost no crystal grains grown on the substrate. When the film is prepared with surfactant NaOA, it is tightly bonded with the substrate. The carboxyl of the oleate has already chelated with a RE atom30. So the remaining unassociated carbon-carbon double bond of oleate is a rational candidate for the bonding with the substrate.

Figure 2 (a) FT-IR spectra of Silica Glass and OA/Silica Glass. (b) Photoluminescence spectra of OA/ Silica Glass, OA and Silica Glass excited at 320 nm. OA-Y complex film combined with a quartz glass is then prepared for verifying the bonding. OA-Y complexes suspension obtained from stirring NaOA and YCl3 aqueous solution are


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transferred into a 100 ml PPL vessel in which two superimposed silica glasses are placed. The vessel is then sealed and heated up to 220 °C for 24 h (Supporting information methods). The obtained “silica glasses” is named as OA/Silica Glass. Figure 2 shows the FTIR spectra and PL spectra of a referential silica glass and the lower surface of the upper piece of OA/Silica Glass which is placed in the confined space. The OA/Silica Glass sample for FTIR measurement is obtained by scraping the surface and grinding the obtained particles with KBr and then tableting. Figure 2 (a) shows that the absorption peak centred at around 3450 cm-1 of Silica Glass corresponds to the overlapped two O-H stretching bands of absorbed water molecules and SiO-H. The band appearing at 1630 cm-1 is assigned to water molecules. The band at 1100 cm-1 represents stretching vibration absorption of Si-O. A broad band of OA/Silica Glass appearing at 3130-3290 cm-1 shows up and can be assigned to associated O-H of carboxyl, which exactly corresponds to complexation of OA and Y atom. Therefore, OA is proved linked with the substrate. Meanwhile, the PL spectra are tested as shown in Figure 2(b) to further demonstrate the existence of OA on substrate. When excited with 320 nm incident light, 420 nm emission of the silica glass is obtained. The OA and OA/Silica Glass possess the same 404 nm emissions, which shows the existence of OA on substrate. Besides, the FTIR spectrum of OA/Silica Glass shows that the absorption peaks of water molecules at 3440 cm-1 and 1630 cm-1 are weaken, which declares the decrease of hydrophilic Si-O-H groups on the surface. Therefore, it is inferred that Si-O-H bond and carbon-carbon double bond participate in the additive reaction to realize the link of OA and substrate. Meanwhile, it is worth mentioning that ion product of water rapidly increases with the increase of temperature and pressure and H+ ions are produced. An H+ ion as the electrophilic reagent may participate in the electrophilic addition with the assistance of a hanging oxygen atom with a redundant electron on the surface of silica glass. Therefore, the


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bonding mechanism can be assigned to both the additive reaction of Si-O-H bond and carboncarbon double bond and H+ ions participated electrophilic addition (Figure 1c).

Figure 3 Central FESEM images of (a) U0.5, (b) U0.8, (c) U1, (d) U1.5, (e) U2, (f) U3, (g) C1, (h) C2, and (i) C3 with inserted corresponding marginal images. During the film-formation process the inhaling of precursor solution is a crucial step because it is closely related to the advancing distance of precursors in the confined space, which will influence the density of film. The inhaling of precursor solution is controlled by the dimension of confined space and the concentration of precursors, which therefore both regulate the formation of the UC film and are discussed as follows.


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Space heights between Us and Ms can be regulated by the vertical displacement of Us, which is realized by the equilibrium between complicated fluid impact on Us and weights of Us. So weights of Us are adjusted with different heights (i.e. weights) of Us (set as 0.5 cm, 0.8 cm, 1 cm, 1.5 cm, 2 cm, and 3 cm; as-prepared corresponding Mf are labelled as U0.5, U0.8, U1, U1.5, U2, and U3, respectively) to regulate the space heights. Figure 3a-f shows the distributions of films composed of crystal grains (Figure S11) which is different as the space heights changing. U1 and U1.5 are the densest among the set of the films and are almost overspread. Densities of crystal grains will however decrease no matter the heights of substrate Us decrease or increase. The space heights need to be quantified to analysis the influence of space height on the inhaling of precursor solution. Therefore, the typical space heights for the growth of U0.5, U1 and U3 (between 0.5 mm Us and 1 mm Ms, 1 mm Us and 1 mm Ms, 3 mm Us and 1 mm Ms, respectively) are measured based on the heights of PMMA sheets labelled as H0.5-1, H1-1, and H3-1 produced inside these spaces (Supporting information methods). Marginal heights of H0.51, H1-1, and H3-1 are 7.10 µm, 10.40 µm, and 5.76 µm, respectively as shown in Figure S12. Therefore, U1 with the densest crystal grains is prepared in the highest space and U3 with the sparsest crystal grains is in the minimum one of the three and it is obvious that the higher space within a certain range causes the more dense crystal grains. This is helpful for the confirmation of the influence mechanism of space height on the inhaling of precursor solution. It can be seen from Figure 3a-f that the distribution density of crystal grains of the marginal area is close to that of the central region no matter how high is the space. So it can be inferred that the concentration of precursors inside the space is not that different at different positions of a space. Considering that the given concentration of the outside space is constant, it is surmised that different space heights dramatically change the precursor concentrations into the space due to the complicated


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fluid movement at the space entrance and precursor interactions, which then lead to the different distribution density of U0.5, U1 and U3. Therefore, the space height directly effects the concentration of precursors which are inhaled into the space and the distribution density of crystal grains is concentration-dependent. As a proof of concept test, space-confined UC films are synthesised with increasing precursor concentrations c1, c2, and c3 (Supporting information methods, as-prepared Mf are labelled as C1, C2, and C3). The evolution of crystal grain distribution along with the concentration is demonstrated in Figure 3g-i. The increasing concentration pushes more precursors to enter the space and makes films denser and increasing densities from C1 to C3 therefore lead to the corresponding increasing fluorescence intensities (Figure S14). Therefore, the higher space within a certain range firstly causes the higher concentration, and then the denser crystal grains. As stated, the concentration of inside precursors has a great effect on the density of the film, so does the ambient one and is worth exploring. As shown in Figure S12, central heights of H0.5-1, H1-1 and H3-1 account for 69%, 78% and 71% of corresponding marginal heights, respectively. Therefore, the diffusion of precursor solution from hydrothermal environment to the confined space submits to Fick′ second law (Formula (1)), where the diffusion flux varies at different position as follows:

∂C ∂ 2C =D 2 ∂t ∂x

(1)

Here, C , t , D , and x are concentration, time, diffusion coefficient and position. The precursor concentration decreases as the diffusion distance increases and the thickness of the film decreases accordingly from marginal area to central region (Figure S13). Therefore, if initial precursor concentration is higher, the concentration at central region is higher after precursors


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advance the same distance (Figure S15) and there is going to be more as-prepared crystal grains in central region as shown in Figure 3g-i. When the concentration is small (c1), little crystal clusters composed of crystal grains can be found. When the concentration rises 3 times, the surface of the C3 film is overspread with crystal grains.

Figure 4 (a) The FESEM image of space-confined synthetic UC films. (b) The partial enlarged detail of (a) as arrows marked. (c) XRD pattern of NaYF4:20Yb, 0.5Tm UC films with the standard cubic phase NaYF4 (JCPDS 06-0342) and hexagonal phase NaYF4 (JCPDS 16-0334) as references. Insert: schematic diagram of (101) orientated atoms arrangement of hexagonal NaYF4. (d) Corresponding inverse fast Fourier transform (FFT) image of marked area in (e). Insert: corresponding FFT image in [001] incidence. (e) The TEM image of space-confined synthetic UC film. (f) Crystal lattice fringe image and lattice spacing is 0.195 nm corresponding to the (210) crystal planes of hexagonal phase NaYF4. Insert: selected diffraction spots.


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The special method for the fabrication of nanofilm endows films with unique features closely related to the confined space. Figure 4 presents particular morphology of the NaYF4 UC film Mf, which is stitched by many flower-like crystal druses and a crystal druse is constituted by tightly coupled vein-like distributed crystal grains. The EDS pattern proves the film is mainly constituted by Na, RE and F elements (Figure S16). The XRD pattern (Figure 4) confirms hexagonal phase NaYF4 and the film is highly (101) orientated even with different precursor concentration (Figure S17). The TEM image obtained as shown in Schematic S1 offers a further evidence of the hexagonal structure. Crystalline interplanar spacing is 0.195 nm corresponding to the (210) crystal planes of hexagonal phase NaYF4. The inverse fast Fourier transform image presents the regular arrangement of crystal lattice points. However, XRD patterns of UCNPs prepared under the same hydrothermal parameters present the mixed hexagonal and cubic crystalline phases (Figure S18). It seems that the confined space is advantageous for the crystal growth of thermodynamically stable hexagonal phase. It is because that the fluid impact on atoms inside the space is limited. When atoms are deposited as adatoms onto the surface of existing islands on the substrate31, the weaken fluid impacts make adatoms nearly insusceptible and energetic to assemble in thermodynamically stable way at appropriate temperature and time. Therefore, the regular assembly leads to the orientation of the film. Meanwhile, the layer-layer growth of well-assembled atoms helps to bring about smooth surface32 and the thickness is only about 120 nm (Figure 1). Besides, the smooth surface of the film and matched refractive indexes of the silica glass and the composite film (both about 1.46 obtained from Abbe refractometer) contribute to the high transmittance of Mf (Figure 1) which makes it comes into being of optionally practical use of the composite film without considering forward or reverse placements (Figure S19). Furthermore, the transparent composite film may be coupled with a reflecting layer


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at the rear to enhance the absorption of exited photons and to improve the overall fluorescence (Figure S20). The device is maybe able to serve in photovoltaic system for the desire of enhancing solar cell efficiency4. Besides, it is found that the space-confined synthetic method has great influence on the crystal crystallinity of the film. Wang et al reports that packing manners of atoms is limited by the dimensionality of space33. So comparing TEM images of hexagonal NaYF4 crystal grains with the size of both about 10 nm of the space-confined film Mf (Figure 4) and the film Uf directly grown in the hydrothermal environment (Figure S2), the former shows the straight lattice fringe and the regular arrangement of crystal lattice points, and the latter however shows lots of crystal lattice distortions and inserted atomic planes in marked circles, i.e. lattice defects. Therefore, the confined space has the advantage to push atoms to jump into the existing defect sites when moving along a step edge to decrease crystal defects and improve the lattice perfection of the crystal grain rather than stay above the island or move somewhere else.


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Figure 5 (a) Schematic diagram of the compacted arrangement of atoms arising from confined assembling space and resulted enhanced fluorescence emissions. (b, c, d) are UC fluorescence spectra of space-confined synthetic UC film and (b) hydrothermal UCNPs, (c) PDMS composite film, (d) self-assembly film with inserted corresponding schematic diagrams of films, respectively. The displayed signals in 300-320 nm are 3000 times magnified. Excitation is from 980 nm laser with the power density of 7.7 W/cm2. As a photoluminescence material, fluorescence performances of space-confined UC NaYF4:20Yb, 0.5Tm film needs to be stated and is compared with PDMS composite UC film and self-assembly UC film (Supporting Information Methods, Figure 5) which both have acquired lots of favour3, 34-36. Functional luminescence units in the two films are hexagonal NaYF4 UCNPs


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synthesised by thermal decomposition method (Figure S21) which is widely applied in recent researches3, 10, 37, 38. UCNPs with the same stoichiometry as the space-confined film possess the size of about 37 nm. The transmittance differences of all the three films are small especially at 980 nm to decrease the influence on fluorescence performances caused by absorbance differences (Figure S22). Table 1. Upconversion intensity ratios of confined-space film and self-assembly film, PDMS composite film, hydrothermal UCNPs, and upconversion quantum yield ratios. Intensity ratios

UC RQY

λ (nm) Ic-F/Iself-F

Ic-F/IPDMS-F

Ic-F/IHNPs

QYc-F/QYTNPs

QYc-F/QYHNPs

300-850

2.8

32.6

4.3

3.4

15.4

300-400

3.9

67.1

4.5

4.7

16.1

346

5.3

66.2

5.6

6.4

20.0

361

4.2

54.6

6.8

5.1

24.3

* c-F represents space-confined film, self-F and TNPs both represent thermal decomposition UCNPs self-assembled on a silica glass, PDMS-F represents PDMS composition film and HNPs represents hydrothermal UCNPs deposited on a silica glass.

The space-confined film is found to have enhanced overall intensities (300-850 nm, Figure S23). Table 1 lists the intensities ratio of space-confined film (labelled as c-F) and other UC systems (self-F or TNP: self-assembly film, PDMS-F: PDMS composition film and HNPs: hydrothermal UCNPs). The integral intensities ratio of space-confined film and self-assembly film is 2.8, and the ratio of space-confined film and PDMS composite film is up to 32.6. Besides, the spaceconfined film is found to have enhanced short-wave, especially ultraviolet (UV) fluorescence (Figure 5). Fluorescence enhancements of the space-confined film increase with the decreasing of the wavelength, which are up to 5.3 and 66.2 times at 346 nm relative to self-assembly film and PDMS composite film, respectively. Fluorescence enhancements ratios in 300-400 nm are


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3.9 and 67.1, respectively. These fluorescence enhancements can be ascribed to the larger crystal grains sizes along with the decreased defects17. Besides, the direct-emission mode avoids the loss arising from the scattering medium compared with the PDMS composite film. Since UCNPs employed in these two references are synthesised by thermal decomposition method. The fluorescence performance of the space-confined film needs to be compared with hexagonal hydrothermal UCNPs counterparts to reveal the contribution of the confined space. In comparison with hexagonal hydrothermal UCNPs which are obtained under higher reaction temperature and deposited on a silica glass, the space-confined film possesses enhanced integral and UV emission intensities as well and the enhancement ratios are 4.3 and 4.5, respectively. The FESEM images show crystal grains of the film are 3 times larger than hydrothermal UCNPs (Figure S24). So the confined growing space incubates a stable environment for the crystal grains to grow bigger which is beneficial for the fluorescence enhancement. The UC quantum yield (QY) which evaluates the photon conversion abilities needs to be considered to grade the space-confined film. However, the present measurement inaccuracy by utilizing an integrating sphere and a commercial fluorometer23 is still large because the excitation photons is much more than the emitted ones24. A modified relative QY is calculated according to the report of Chen et al39. The QY of the UC material can be calculated based on a known QY of a reference as shown in Formula (2):

QYUC

E = QYref  UC E  ref

  Aref  I ref      AUC  IUC

  nUC     nref

  

2

(2)

Here, E, A, I, n are numbers of the emitted photons, numbers of the absorbed photons, relative intensity of the exciting light and the average refractive index of the solvent. The subscripts ref


20

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and UC refer to the reference and the objective UC material. Due to the complicacy of comparing a film with dispersion solution, the QY of c-F is compared with TNPs and HNPs according to Formula (3): QYUC1  EUC1   AUC 2   IUC 2   nUC1  =     QYUC 2  EUC 2   AUC1   IUC1   nUC 2 

2

(3)

Here, the subscripts 1 and 2 refer to two objective UC materials. TNPs and HNPs are selfassembled and deposited on silica glasses, respectively. Absorptions can be obtained from Figure S22. The dispersive mediums for the three systems can be assigned to the air with the refractive index of 1. The intensities of the exciting light are considered as the same in one PL measurement. The calculated RQYs are listed in Table 1. The overall QY enhancements of the space-confined film in 300-850 nm are also obtained. QYc-F/QYTNPs and QYc-F/QYHNPs are 3.4 and 15.4. The QYc-F in the UV region are 4.7 and 16.1 times enhanced relative to QYTNPs and QYHNPs and the enhancement ratios are up to 6.4 and 20.0 at 346 nm. The space-confined synthetic UC film possesses enhanced UC fluorescence, especially the UV segment, which needs to be illustrated. The surface morphology as a typical influence is firstly investigated. Morphology of the films is regulated by adjusting the molar ratio of NaOA and RE (Figure S5) set as 0.5, 1 and 1.5 (labelled as NaOA-0.5, NaOA-1 and NaOA-1.5), which are pine-like, ribbon-like and ellipsoid-like. The morphology does have an effect on UV performance because INaOA-1/INaOA-0.5 and INaOA-1/INaOA-1.5 are 2.0 and 1.3 in 300-400 nm, respectively, but INaOA-1/INaOA-0.5 and INaOA-1/INaOA-1.5 are 1.1 and 0.7 in 300-850 nm, respectively. Therefore in spite of the ability to adjust emitted wavelengths40, 41, the surface morphology may be not a key factor because it is not adequate for the remarkable fluorescence enhancement of the space-confined space relative to UCNPs. Additionally, the thickness of film as a usual factor is


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considered. As shown in Figure S13, thicknesses of the marginal area and central region of C3 are about 200 nm and 123 nm, respectively. The fluorescence spectra show that even though the thickness difference is up to about 80 nm nearly half of the thickness of the marginal area, the fluorescence intensities present small difference. Therefore the thickness fails to serve as a great effect on the fluorescence enhancement. Consequently, the larger sizes of crystal grains of the film along with less crystal defects contribute to the high populations of high energy levels which are closely related to the crystallinity. It is acknowledged that surface characteristics of UCNPs are important for the UC efficiency42, because numerous RE dopants are exposed to surface deactivations caused by such as surface defects and lattice strains with high phonon energy29, 43. The large size minimizes the migration of energy to defects, which favors the high populations of high energy levels to realize strong emissions of high-energy photons44. Besides, the low intrinsic defect density also reduces the possibility for excited dopants being deactivated directly by adjacent quenching centers. Table 2. Upconversion intensity ratios of confined-space film, thermal deposition UCNPs and hydrothermal UCNPs after normalized at 802 nm of each radiative transitions of Tm. Radiative Transition 1 1

1

3

λ (nm)

Normalized Intensity ratios Ic-F/ITNPs

Ic-F/IHNPs

I6

→

3

F4

346

2.1

1.3

D2

→

3

H6

361

1.7

1.6

→

3

F4

452

1.5

1.2

→

3

H5

510

1.8

1.2

→

3

H4

578

6.6

1.9

→

3

H6

475

0.7

1.0

→

3

F4

646

0.9

1.1

→

3

H6

802

1.0

1.0

G4

H4


22

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The space-confined synthetic UC film which possesses higher UV QY provides a positive environment for high population of 3P2, 1I6 and 1D2 energy levels of Tm ions. Among all these UC material systems mentioned above, only the space-confined film has the 5-photons 3P2→3F4 (309 nm) transition (Figure 5) due to the efficient 3P2 population as Wang et al45 found. Besides, strong multiphoton transitions are observed, including 5-photons 1I6→3F4 (346 nm) and 4photons 1D2→3H6 (362 nm), 1D2→3F4 (452 nm) transitions. After normalized at 802 nm (3H4→3H6) (Figure S23), 346 nm, 362 nm and 452 nm emissions of the space-confined film are still stronger than thermal decomposition UCNPs (i.e. the self-assembly film) and hydrothermal UCNPs (the PDMS composite film are not included in the compare considering the influence of polymer matrix on fluorescence). Table 2 lists the relative fluorescence intensity ratios. Radiation transitions from 1I6 and 1D2 energy levels of the space-confined film are relatively stronger than the two kinds of UCNPs. But radiation transitions from 1G4 and 3H4 states corresponding to 1G4→3H6 (475 nm), 1G4→3F4 (646 nm) and 3H4→3H6 (802 nm) transition are not stronger. Because the cross relaxation 1G4+3H4→3F4+1D2 is more inclined to occur in the space-confined film, which causes the relatively sacrificial emissions from 1G4 and 3H4 levels and increased populations of 1D2 level45 to emit 362 nm and 452 nm photons and further increased populations of 3P2 and 1I6 energy states.


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Figure 6 Log - log plots of the UC emission intensity versus the excitation power for spaceconfined synthetic UC film. The numbers indicate the slope at low and high pump power, respectively. The dot dash lines correspond to the highest power of Figure S27. The excitation power dependence of the space-confined film is then discussed. Figure 6 shows the photon numbers of the film absorbed for radiative transitions. Calculated photon numbers for 476 nm and 647 nm (Figure S25) are smaller than its actual value 3 due to the cross relaxation. Calculated photon numbers of other emissions are nearly consistent with their actual values and present small difference under wide range of excitation power except 346 nm emission which is a little smaller than actual value because of the inevitable nonradiative transition at the high excitation state. However, absorbed photons numbers for UV transitions of hydrothermal and thermal decomposition UCNPs both deviate from their actual values and decrease within narrow range of excitation powers (Figure S26 and S27), which indicates the serious nonradiative relaxation45. So the construction of space-confined film provides a way for pursuing the more effective radiative transition under wide range of excitation powers.

Figure 7 UC fluorescence lifetime spectra of space-confined synthetic UC film, hydrothermal UCNPs and thermal decomposition UCNPs.


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As the fingerprints of energy transfer process, decay lifetimes need to be analyzed to uncover the energy evolvement under excitation. Figure 7 shows the UC fluorescence lifetime spectra of space-confined synthetic UC film, hydrothermal UCNPs and thermal decomposition UCNPs. Decay lifetimes are determined by radiative and nonradiative transition lifetimes and any process competing with the radiative transition causes the decrease of excited state lifetimes. The lifetimes of 3H4 (→3H6, 802 nm), 1G4 (→3F4 and 3H6, 647 nm and 476 nm), 1D2 (→3F4 and 3H6, 451 nm and 361 nm) and 1I6 (→3F4, 345 nm) levels of the space-confined film are 1.05 ms, 0.70 ms, 0.34 ms and 0.29 ms, respectively. It is apparent that the decay lifetimes of higher excitation states are shorter, which is because that the population of higher excitation state needs more absorbed photons. Therefore, high population of higher excitation states is harder to be achieved. However, the lifetimes of 1I6 and 1D2 levels of the space-confined film are longer than those of the two kinds of UCNPs, which indicates that the film has the ability to realize higher population of high energy levels and higher probabilities of radiation transitions to emit UV photons with high energies. Besides, decay lifetimes of all the excitation states of the space-confined film are longer than the two kinds of UCNPs (Figure 7 and S28). Therefore, the film is demonstrated to be an excellent UC material for the more efficient radiative transitions.


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Figure 8 (a) Schematic diagram of undersurface NIR-induced photochemical synthesis of acrylate modified polymer. (b) The transmittance spectrum of photoinitiator 1173. (c) The photograph of hand painted Taiji pattern by NIR-induced photochemical reaction of acrylate modified polymer. As a demonstration, the UV-enhanced space-confined UC film is able to serve as a medium to trigger the NIR-induced undersurface photochemical reaction. As shown in Figure 8, the homogeneous mixture solution composited of acrylate modified oligomer, MMA and photoinitiator 1173 is poured into a customized Teflon vessel. The as-prepared composite UC film is placed into the solution cushioned with two pieces of glass on both sides. The emitted UV fluorescence from the UC film under a 980 nm laser excitation can be absorbed by the photoinitiator 1173. Active radicals are then formed and trigger the quick polymerization of oligomers and it can almost be finished within about 5 min (Figure S29). The visible blue emissions serve as the indicator lights. Besides, intricate patterns can be obtained on the UC film


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by slowly hand painting with a 980 nm laser as shown in Figure 8c and the extra unreacted organic molecules on the film can be easily washed away by alcohol. Therefore, the UVenhanced UC film has a great potential for 3D printing. Conclusion In summary, a space-confined synthetic UC film is successfully prepared and is highly transparent, robust, oriented, and the morphology of the film is controllable. The formation mechanism of the film is clearly illustrated in this paper. Confined space provides a stable environment for atoms to assembly in a more orderly way and is beneficial for the crystal grains of the film to grow bigger. Therefore, the film is more inclined to be thermodynamically-stable hexagonal phase with decreased crystal defects. What is more meaningful is that the UC film grown in the special environment is found to have higher populations of high energy levels and higher QYs than UCNPs synthesized with hydrothermal and thermal decomposition methods. Therefore, the film possesses enhanced short-wave (300-460 nm) relative fluorescence within wide range of excitation powers. Besides, such an efficient UC film with enhanced UV fluorescence is able to realize undersurface photochemical reaction and has a great potential for 3D printing, as well as composite photocatalyst materials, all-solid short-wavelength lasers and photovoltaic materials. ASSOCIATED CONTENT Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.” Method details, schematic diagram, additional FESEM and TEM images, UC fluorescence, PL decay lifetimes, FT-IR spectra, XRD and EDS patterns.


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AUTHOR INFORMATION Corresponding Author *E-mail: [email protected], *E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT The authors thank Professor Feng Xu of Southeast University for the guidance of the paper. This work was financially supported by the Program for the National Natural Science Foundation of China (No. 51303079), the Natural Science Foundation of Jiangsu Province (No. BK20141459), the Key University Science Research Project of Jiangsu Province (No. 10KJA430016), and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) is gratefully acknowledged. REFERENCES (1) Saboktakin, M.; Ye, X.; Chettiar, U. K.; Engheta, N.; Murray, C. B.;Kagan, C. R. ACS Nano 2013, 7, 7186-7192. (2) Meruga, J. M.; Baride, A.; Cross, W.; Kellar, J. J.;May, P. S. J Mater Chem C 2014, 2, 22212227. (3) Deng, R.; Qin, F.; Chen, R.; Huang, W.; Hong, M.;Liu, X. Nature Nanotechnology 2015, 10, 237-242. (4) Huang, X.; Han, S.; Huang, W.;Liu, X. Chem Soc Rev 2013, 42, 173-201. (5) Chen, X.; Xu, W.; Zhang, L.; Bai, X.; Cui, S.; Zhou, D.; Yin, Z.; Song, H.;Kim, D.-H. Adv Funct Mater 2015, 25, 5462-5471. (6) Shen, J.; Chen, G.; Vu, A.-M.; Fan, W.; Bilsel, O. S.; Chang, C.-C.;Han, G. Adv Optical Mater 2013, 1, 644-650. (7) Ding, M.; Chen, D.; Wan, Z.; Zhou, Y.; Zhong, J.; Xia, J.;Ji, Z. J Mater Chem C 2015, 3, 5372-5376. (8) Yan, L.; Chang, Y.-N.; Yin, W.; Tian, G.; Zhou, L.; Hu, Z.; Xing, G.; Gu, Z.;Zhao, Y. Adv Eng Mater 2015, 17, 523-531.


28

Page 29 of 31

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


(9) Watanabe, S.; Asanuma, T.; Sasahara, T.; Hyodo, H.; Matsumoto, M.;Soga, K. Adv Funct Mater 2015, 25, 4390-4396. (10) Chen, X.; Xu, W.; Zhang, L.; Bai, X.; Cui, S.; Zhou, D.; Yin, Z.; Song, H.;Kim, D.-H. Adv Funct Mater 2015, 25, 5462-5471. (11) Saboktakin, M.; Ye, X.; Oh, S. J.; Hong, S.-H.; Fafarman, A. T.; Chettiar, U. K.; Engheta, N.; Murray, C. B.;Kagan, C. R. ACS Nano 2012, 6, 8758-8766. (12) Yin, Z.; Zhou, D.; Xu, W.; Cui, S.; Chen, X.; Wang, H.; Xu, S.;Song, H. ACS applied materials & interfaces 2016, 8, 11667-11674. (13) Wagata, H.; Wakabayashi, T.; Suzuki, S.; Tanaka, M.; Nishikiori, H.; Oishi, S.;Teshima, K. Crystal Growth & Design 2013, 13, 1187-1192. (14) Que, W.; Kam, C. H.; Zhou, Y.; Lam, Y. L.;Chan, Y. C. J Appl Phys 2001, 90, 4865. (15) Huang, W.; Lu, C.; Jiang, C.; Wang, W.; Song, J.; Ni, Y.;Xu, Z. J Colloid Interface Sci 2012, 376, 34-39. (16) Yuan, D.; Tan, M. C.; Riman, R. E.;Chow, G. M. J Phys Chem C 2013, 117, 13297-13304. (17) Wang, F.; Wang, J.;Liu, X. Angew Chem Int Ed 2010, 49, 7456-7460. (18) He, C.; Qin, G.; Zhao, D.; Chuai, X.; Wang, L.; Zheng, K.;Qin, W. J Nanosci Nanotechnol 2014, 14, 3831-3833. (19) Uda, S.; Adachi, K.; Inaba, K.;Fukuda, T. Jpn J Appl Phys 1997, 36, 41-44. (20) Jia, H.; Xu, C.; Wang, J.; Chen, P.; Liu, X.;Qiu, J. CrystEngComm 2014, 16, 4023. (21) Jia, H.; Zheng, S. H.; Xu, C.; Chen, W. B.; Wang, J. C.; Liu, X. F.;Qiu, J. R. Adv Energy Mater 2015, 5, 1401041. (22) Tian, L.; Wang, P.; Wang, H.;Liu, R. RSC Advances 2014, 11, 1-3. (23) Boyer, J. C.;van Veggel, F. C. Nanoscale 2010, 2, 1417-1419. (24) Zhou, J.; Liu, Q.; Feng, W.; Sun, Y.;Li, F. Chemical reviews 2015, 115, 395-465. (25) Chen, G.; Ohulchanskyy, T. Y.; Kumar, R.; Ågren, H.;Prasad, P. N. ACS Nano 2010, 4, 3163-3168. (26) Bogdan, N.; Vetrone, F.; Ozin, G. A.;Capobianco, J. A. Nano Lett 2011, 11, 835-840. (27) Chen, G.; Damasco, J.; Qiu, H.; Shao, W.; Ohulchanskyy, T. Y.; Valiev, R. R.; Wu, X.; Han, G.; Wang, Y.; Yang, C.; Agren, H.;Prasad, P. N. Nano Lett 2015, 15, 7400-7407. (28) Ding, M.; Lu, C.; Song, Y.; Ni, Y.;Xu, Z. CrystEngComm 2014, 16, 1163-1173. (29) Sun, Y.; Chen, Y.; Tian, L.; Yu, Y.; Kong, X.; Zhao, J.;Zhang, H. Nanotechnology 2007, 18, 275609. (30) Ye, X.; Chen, J.; Engel, M.; Millan, J. A.; Li, W.; Qi, L.; Xing, G.; Collins, J. E.; Kagan, C. R.; Li, J.; Glotzer, S. C.;Murray, C. B. Nature Chem 2013, 5, 466-473. (31) Ratsch, C.;Venables, J. A. Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 2003, 21, S96. (32) Levi, A. C.;Kotrla, M. Journal of Physics: Condensed Matter 1997, 9, 299–344. (33) Wang, Z.; Shi, Z.;Gu, Z. Chemistry, an Asian journal 2010, 5, 1030-1038. (34) Wang, F.; Han, Y.; Lim, C. S.; Lu, Y.; Wang, J.; Xu, J.; Chen, H.; Zhang, C.; Hong, M.;Liu, X. Nature 2010, 463, 1061-1065. (35) Zheng, T.; Sun, L.-D.; Zhou, J.-C.; Feng, W.; Zhang, C.;Yan, C.-H. ChemComm 2013, 49, 5799-5801. (36) Ye, X.; Collins, J. E.; Kang, Y.; Chen, J.; Daniel T. N. Chen; Yodh, A. G.;Murray, C. B. PNAS 2010, 107, 22430-22435. (37) Feng, A. L.; You, M. L.; Tian, L.; Singamaneni, S.; Liu, M.; Duan, Z.; Lu, T. J.; Xu, F.;Lin, M. Scientific reports 2015, 5, 7779.


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Page 30 of 31

(38) Ding, M.; Ni, Y.; Song, Y.; Liu, X.; Cui, T.; Chen, D.; Ji, Z.; Xu, F.; Lu, C.;Xu, Z. J Alloys Compd 2015, 623, 42-48. (39) Chen, G.; Ohulchanskyy, T. Y.; Liu, S.; Law, W.-C.; Wu, F.; Swihart, M. T.; gren, H. A.;Prasad, P. N. Acs Nano 2012, 6, 2969-2977. (40) Ding, M.; Chen, D.; Yin, S.; Ji, Z.; Zhong, J.; Ni, Y.; Lu, C.;Xu, Z. Scientific reports 2015, 5, 12745. (41) Ding, M.; Yin, S.; Ni, Y.; Lu, C.; Chen, D.; Zhong, J.; Ji, Z.;Xu, Z. Ceram Int 2015, 41, 7411-7420. (42) Ding, M.; Chen, D.; Ma, D.; Dai, J.; Lia, Y.;Ji, Z. J Mater Chem C 2016, 4, 2432-2437. (43) Chen, G.; Qiu, H.; Prasad, P. N.;Chen, X. Chemical reviews 2014, 114, 5161-5214. (44) Wang, J.; Deng, R.; MacDonald, M. A.; Chen, B.; Yuan, J.; Wang, F.; Chi, D.; Hor, T. S. A.; Zhang, P.; Liu, G.; Han, Y.;Liu, X. Nature materials 2013, 1-6. (45) Wang, G.; Qin, W.; Wang, L.; Wei, G.; Zhu, P.;Kim, R. Opt Express 2008, 16, 1907-1914.


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For Table of Contents Use Only

Near-Infrared Upconversion Transparent Inorganic Nanofilm: Confined-Space Directed Oriented Crystal Growth and Distinctive Ultraviolet Emission Xiaoxia Liu,†,§,┴ Yaru Ni,*,†,§, ┴,ǁ Cheng Zhu, †,§, ┴ Liang Fang,†,§, ┴ Song Hu, †,§, ┴ Zhitao Kang,‡ Chunhua Lu,*,†,§, ┴ and Zhongzi Xu†,§, ┴

The space-confined synthetic UC film with orderly atoms assembly is successfully prepared and the as-prepared film is highly transparent, robust, orientated, and controllable of morphology, and possesses enhanced ultraviolet fluorescence.


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Confined-Space Directed Oriented Crystal Growth ... - ACS Publications

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