CH3NH3PbBr3 Perovskite Nanocrystals Encapsulated in Lanthanide

Research Article Cite This: ACS Appl. Mater. Interfaces 2018, 10, 27875−27884

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CH3NH3PbBr3 Perovskite Nanocrystals Encapsulated in Lanthanide Metal−Organic Frameworks as a Photoluminescence Converter for Anti-Counterfeiting Diwei Zhang,† Wei Zhou,‡ Quanlin Liu,† and Zhiguo Xia*,† †

School of Materials Sciences and Engineering, University of Science and Technology Beijing, Beijing 100083, P. R. China Key Laboratory of Cosmetic, China National Light Industry, Beijing Technology and Business University, Beijing 100048, P. R. China

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‡

ABSTRACT: The increasing demands for optical anti-counterfeiting technology require the development of versatile luminescent materials with multiple models and tunable photoluminescence. Herein, the combination of luminescent perovskite nanocrystals and lanthanidebased metal−organic frameworks (Ln-MOFs) has been developed to offer such a high-tech anti-counterfeiting solution. The hybrid materials have been fabricated via the encapsulation of perovskite CH3NH3PbBr3 nanocrystals in europium-based metal−organic frameworks (EuMOFs) and they display multistage anti-counterfeiting behavior. CH3NH3PbBr3@Eu-MOF hybrids were developed in a two-step process, where the PbBr2@Eu-MOF precursor was formed first and, then, the composites can be formed quickly by the addition of CH3NH3Br into the precursors. Accordingly, the hybrid composites exhibited both excitation wavelength and temperature-dependent luminescence properties in the form of powders or films. Furthermore, the photoluminescence of the CH3NH3PbBr3@Eu-MOF composites can be quenched and recovered through water immersion and CH3NH3Br conversion, and the anticounterfeiting applications have also been discussed. Therefore, this finding will open the opportunity to fabricate the hybrid materials with controlled photoluminescence properties, and it also acts as the emerging anti-counterfeiting materials in versatile fields. KEYWORDS: CH3NH3PbBr3, lanthanide-based metal−organic frameworks, composite, photoluminescence conversion, anti-counterfeiting

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INTRODUCTION

models and tunable photoluminescence for the high-level anticounterfeiting protection. In recent years, the halide perovskite MPbX3 (M = CH3NH3, Cs; X = Cl, Br, I) NCs, appeared as fascinating luminescent materials due to the superior optoelectronic properties and versatile applications.19−21 In general, hybrid organic−inorganic CH3NH3PbX3 NCs demonstrate intensive photoluminescence (PL) intensity, relatively high PL quantum yields (PLQY), and tunable emission depending on halide anions.22,23 However, the CH3NH3PbX3 NCs often exhibit relative poor stability, which restricted their practical applications. On the contrary, it indicated that these perovskite NCs presented heat-dependent abilities, which emitted photoluminescence at room temperature and quenched when the temperature was heated to a certain temperature.24 By taking this for granted, the fluorescence quenching of perovskite NCs for polar solvents can also be used as the advantages of anti-counterfeiting applications, and it can be recombined by using a CH3NH3Br trigger.25,26 Thus, the perovskite CH3NH3PbX3 NCs reveal different PL functions

The development of anti-counterfeiting technologies has attracted particular attention to prevent the increasing counterfeits on the current market including the economic and security implications for different requirements and users including the government, industry, and consumers.1,2 However, the traditional methods were not very effective since some of them may be quickly outdated or duplicated elsewhere. To this end, new techniques are essential to show a high security level and many of these technologies have been made by combining two or more techniques to increase the security level.3−5 Fluorescence materials, owing to their high photoluminescence (PL) intensity/efficiency and tunable excitation/emission wavelength, were widely used in anticounterfeiting technologies.6,7 So far, inorganic semiconductor nanocrystals (NCs), organic dyes, transition-metal complexes, carbon dots, and upconversion nanoparticles have been extensively investigated as luminescent materials for targeted applications.8−15 To date, most advanced anti-counterfeiting materials and technologies were based on multiple excited sources including the ultraviolet (UV), IR, and near infrared light or thermal activation.16−18 Accordingly, it becomes a challenge to fabricate the composite materials with multiple © 2018 American Chemical Society

Received: June 24, 2018 Accepted: July 27, 2018 Published: July 27, 2018 27875

DOI: 10.1021/acsami.8b10517 ACS Appl. Mater. Interfaces 2018, 10, 27875−27884

Research Article

ACS Applied Materials & Interfaces

Figure 1. (a) Schematic illustration targeted the two-step fabrication of CH3NH3PbBr3@EuBTC composites including (1) the PbBr2@EuBTC precursor prepared by a solvothermal method. (2) CH3NH3PbBr3@EuBTC composites precipitated with the addition of CH3NH3Br solution. The two dotted frames give the crystal structures of the PbBr2@EuBTC (left) and CH3NH3PbBr3@EuBTC (right) along the b and c axes. Optical images of CH3NH3PbBr3@EuBTC powder under the 254 nm (b) and 365 nm (c) UV lamp are shown as a comparison.

CH3NH3PbBr3 NCs was quenched with intrinsic red emission of the Eu-MOFs. It is found that the photoluminescence conversion between green and red can be repeatedly realized in the CH3NH3PbBr3@Eu-MOF composite, suggesting a great potential in multimodal optical anti-counterfeiting applications.

demonstrating the potential for anti-counterfeiting applications, however, the direct use of perovskite NCs is infeasible for the stability issues. Porous crystalline materials, metal−organic frameworks (MOFs), possess versatile advantages including different coordination geometries, unique chemical functions (absorption/catalyst), and useful physical properties (luminescent/ magnetic), and so on.27−29 Recently, MOFs have been extensively investigated with special utilizations as host matrices for photoluminescence.30,31 In particular, lanthanide MOFs (Ln-MOFs) are getting much more attention and many guest members including the carbon dots, metal nanoparticles, and dye molecules, have also been incorporated into MOFs to design new multifunctional MOF-based composites.32−35 The unique luminescence properties of lanthanide MOFs are featured as strong and sharp emission bands, and the specific lanthanide ion has an inherent emission peak and is not dependent on the environment. The above advantages make them ideal candidates in optical anti-counterfeiting applications.36,37 Meanwhile, the combination of perovskite NCs and Ln-MOFs with an improved synergetic effect for developing advanced anti-counterfeiting materials is still in its infancy and many challenges exist. In this work, we fabricated the perovskite CH3NH3PbBr3 NCs encapsulated in the europium-based MOFs (Eu-MOFs) via a two-step synthesis method. The PbBr2@Eu-MOF precursor was firstly formed via a solvothermal method and, then, the CH3NH3PbBr3@Eu-MOF composites can be formed quickly using a CH3NH3Br solution that reacts with the precursors. Subsequently, the CH3NH3PbBr3@Eu-MOF composite displays outstanding green and red emissions under the 365 and 254 nm UV lamp, respectively. Intriguingly, obvious color evolution from green to red emission was observed when the excited wavelength changed from 365 to 254 nm. Furthermore, the same color variation was observed in a wide temperature range from 25 to 200 °C under the excitation wavelength of 317 nm. Finally, we utilized a mixture of PbBr2@Eu-MOF solution as an anti-counterfeiting ink to write some signals on the paper. Then the perovskite CH3NH3PbBr3 NCs in the Eu-MOF host were destroyed by water immersion, thus, the green luminescence of the

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EXPERIMENTAL SECTION

Materials. H3BTC (Purity of 98%, Aladdin Chemistry Co., Ltd), Eu(NO3)3·6H2O (Purity of 99.9%, Aladdin Chemistry Co., Ltd), CH3NH3Br (30 mL of methylamine 33% in methanol, Aladdin Chemistry Co., Ltd), HBr (48 wt % in water by weight, Aladdin Chemistry Co., Ltd), N,N-dimethylformamide (DMF) (Purity of 99.5%, Aladdin Chemistry Co., Ltd), and diethyl (Purity of 99%, Sinopharm Chemical Reagent Co., Ltd). Precursor Synthesis. As reported in the reference and our work on typical synthesis,38,39 0.5 mmol Eu(NO3)3·6H2O, 0.5 mmol 1,3,5trimesic acid (H3BTC), 20 mL N,N-dimethylformamide (DMF), and 5 mL ethanol were placed in a 50 mL Teflon-lined stainless steel autoclave, which was kept at 120 °C for 2 days to crystallize micronscale EuBTC composites. When the reaction is completed, the precipitates were isolated and washed with DMF/ethanol several times. Then, the samples were dried in a vacuum oven at 80 °C for 12 h. Different PbBr2@EuBTC composites were prepared by adjusting the concentrations of PbBr2, whereas other reaction parameters were fixed. Synthesis of CH3NH3PbBr3@EuBTC Composites. The PbBr2@ EuBTC precursors were added into 5 mL ethanol solution of CH3NH3Br (11.2 mg, 0.1 mmol) for 10 min which led to the formation of CH3NH3PbBr3@EuBTC composites as the precipitates. Fabrication of CH3NH3PbBr3@EuBTC Composite Polydimethylsiloxane (PDMS) Film. The PDMS containing CH3NH3PbBr3@EuBTC composites was added into the matrix and then heated at 80 °C to obtain flower patterns. When the heartshaped patterns were solidified, the PDMS was further coated onto the matrix surface. Then the film was formed after drying at 80 °C. Accordingly, the heart-shaped patterns were sandwiched and coated with PDMS on the other side of the film. Characterization. A PANalytical X’Pert3 Powder diffractometer was used to obtain the X-ray powder diffraction (XRD) patterns operated at 40 kV and 40 mA (Cu Kα radiation. λ = 0.15406 nm). The scanning angle range was 5−50° (2θ). A scanning electron microscope (SEM, JEOL JSM-6510A) was used to analyze the morphology and the corresponding elemental mapping images. A JEM-2010 transmission electron microscope (TEM) operated at 120 keV was used to observed the TEM images and the high-resolution 27876


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Figure 2. (a) XRD patterns of the as-prepared EuBTC, PbBr2@EuBTC, and CH3NH3PbBr3@EuBTC samples, and the simulated patterns of EuBTC and CH3NH3PbBr3 are also given as the comparison. (b) The absorption spectrum of the CH3NH3PbBr3@EuBTC composite (dotted line) and the normalized PL spectra of EuBTC, CH3NH3PbBr3, and CH3NH3PbBr3@EuBTC. XRD patterns (c) and PL spectra of CH3NH3PbBr3@EuBTC depending on the addition amounts of PbBr2. The inset in (d) shows the curve on the emission intensities relative to the PbBr2 amounts. (e) FTIR of EuBTC, PbBr2@EuBTC, CH3NH3PbBr3@EuBTC, and CH3NH3PbBr3. (f) N2 adsorption isotherms obtained for EuBTC and CH3NH3PbBr3@EuBTC.

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transmission electron microscopy (HRTEM) images. The gas adsorption measurements were performed by a Quantachrome Autosorb gas sorption analyzer (Autosorb-iQ-2MP), which was performed at 77 K in a liquid nitrogen bath. A Varian Cary 5 spectrophotometer was used to collect the UV−vis absorption spectra. A fluorescence spectrophotometer (F-4600, Hitachi, Japan) was used to measure the room temperature PL spectra and the temperature-dependent PL spectra, and a computer-controlled electric furnace was used in the latter. A Nicolet FTIR Impact 400 system was used to collect the Fourier transform infrared (FTIR) spectra over the wavenumber range of 500−4000 cm−1.

RESULTS AND DISCUSSION Clearly, Figure 1 shows the schematic synthesis details and the corresponding structural evolution of CH3NH3PbBr3@EuBTC composites. A two-step synthesis strategy is first depicted in Figure 1a. In such a process, a mixture of PbBr2, H3BTC, Eu(NO3)3·6H2O, ethanol, and DMF solvent in a solvothermal treatment is used for the formation of the PbBr2@EuBTC precursors (also see details in the Experimental Section). When the reaction is completed, the as-prepared PbBr2@ EuBTC precursor was collected and dispersed into the 27877


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Figure 3. (a) SEM image of EuBTC and the elemental mapping diagrams of Eu (b), C (c), and O (d) in EuBTC. (e) SEM image of the asprepared PbBr2@EuBTC and the elemental mapping diagrams of Pb (f), O (g), C (h), Eu (i), and Br (j) in PbBr2@EuBTC.

band peaking at 521 nm, and the PLQY value was determined to be 78%. EuBTC demonstrated that the characteristic emission peaks are located at about 593 and 617 nm, respectively. As a comparison, the CH3NH3PbBr3@EuBTC composite gives a series of typical emission peaks at 513, 593, and 617 nm under the excitation wavelength of 302 nm. The emission peak at 513 nm should be ascribed to the band-edge emission of CH3NH3PbBr3 NCs, whereas the red emission at 593 and 617 nm can be assigned to the inherent EuBTC emission. The PLQY values of this composite is determined to be 40.2%. Clearly, the band-edge emission of CH3NH3PbBr3 NCs shows a small blue shift from 521 to 513 nm, which is possibly related to the diameter difference of CH3NH3PbBr3 NCs. Moreover, the absorption spectrum of the CH3NH3PbBr3@EuBTC composite (black dotted line in Figure 2b) shows a band edge at 513 nm, as reported before.43 To obtain the controlled experimental details, we prepared the PbBr2@EuBTC composites containing different amounts (0.1, 0.5, 1, 1.5 and 2 mmol) of PbBr2, and the XRD patterns of this series of CH3NH3PbBr3@EuBTC composites are shown in Figure 2c. It is found that the crystal structure of EuBTC remain invariable and the diffraction peaks of CH3NH3PbBr3 NCs are still observed depending on the addition of different amounts of PbBr2. Figure 2d reveals the PL spectra of this series of samples recorded at the 365 nm excitation. One can find that the luminescence intensity of the CH3NH3PbBr3@EuBTC composite increased first and the maximum can be obtained for 1 mmol of PbBr2 with the increasing amounts of PbBr2. Therefore, the amount of 1 mmol PbBr2 added is selected as the best content in the following experiment. Figure 2e shows the FTIR spectra of the as-prepared samples. With respect to the EuBTC, PbBr2@ EuBTC, and CH3NH3PbBr3@EuBTC samples, there are strong bands in the range of 1615−1558 and 1435−1375 cm−1, which is related to the coordinated carboxylate groups with asymmetrical (ν) and symmetrical (δ) COO− vibrations, respectively. A band at 527 cm−1 is found to be ascribed to the Eu−O stretching vibration. The above results verified that Eu3+ have been coordinated with the 1,3,5-BTC ligands. The broad band centered at 3400 cm−1 was assigned to the hydrogenbonded νOH groups, which came from the adsorbed ethanol. The results verified that ethanol molecules were used as the solvent, and it simultaneously acted as the reactant during the formation of EuBTC. After PbBr2@EuBTC was immersed in CH3NH3Br for several minutes, a peak indicating N−H stretching appeared at 3180 cm−1, which was also verified by the IR of CH3NH3PbBr3 bulk, because of the transformation

CH 3 NH 3 Br ethanol solution to obtain the targeted CH3NH3Br@EuBTC composites. It is found that the colors of PbBr2@EuBTC precursors changed from white to yellow quickly demonstrating the phase formation of the CH3NH3PbBr3@EuBTC composite. Finally, the as-obtained powders can exhibit bright red or green emission, depending on the different excitation wavelengths of 254 or 365 nm, as is verified by the visual photos under the UV lamp shown in Figure 1b,c, respectively. During the synthesis of CH3NH3PbBr3@EuBTC composites, it was related to an in situ fabrication process mechanism. As also shown in Figure 1, the crystal structures of PbBr2@EuBTC and CH3NH3PbBr3@ EuBTC along the b and c axes are given in the two dotted frames, respectively. In the formation process of the PbBr2@ EuBTC precursor, Pb atoms tend to combine with O atoms, and only in the O4 position, which is derived from the hydroxyl group in ethanol, does not bond with the Eu atom in the EuBTC MOFs.40,41 So, the PbBr2 molecules will bond with the O4 atom and exist in the entire framework structure of EuBTC MOFs, which is clearly observed along with the b and c axes of the crystal structure in the black dotted box. Then, the green dotted box shows the in-site formation of the CH3NH3PbBr3 perovskite nanocrystals in the EuBTC matrix. Therefore, during the in situ fabrication process of CH3NH3PbBr3 perovskite nanocrystals in the metal−organic frameworks, the EuBTC matrix acts as a “ligand” dispersing the PbBr 2 molecules. Accordingly, the self-assembly of CH3NH3PbBr3 perovskite nanocrystals was reached at the EuBTC matrix with the introduction of the CH3NH3Br reagent. Figure 2 presents the XRD patterns and PL spectra of the typical CH3NH3PbBr3@EuBTC composites. Firstly, the XRD patterns of EuBTC, PbBr2@EuBTC, CH3NH3PbBr3 bulk, and CH3NH3PbBr3@EuBTC composites are comparatively shown in Figure 2a. Clearly, the diffraction pattern of the as-prepared EuBTC agree well with the simulated pattern of EuBTC. One can also only find the diffraction pattern of EuBTC for PbBr2@ EuBTC, suggesting the high crystallinity of EuBTC. As for CH3NH3PbBr3@EuBTC, the framework structure of EuBTC is well retained as verified by the as-observed diffraction patterns. Apparently, the existence of CH3NH3PbBr3 NCs encapsulated with EuBTC can be confirmed from the two diffraction peaks at 14.9 and 33.7°, corresponding to the (100) and (210) planes of simulated CH3NH3PbBr3.42 Secondly, Figure 2b shows the PL spectra of EuBTC, CH3NH3PbBr3 NCs, and CH3NH3PbBr3@EuBTC composites, respectively. CH3NH3PbBr3 NCs show a green emission 27878


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Figure 4. (a) TEM image of CH3NH3PbBr3@EuBTC suggesting the existence of CH3NH3PbBr3 NCs, as also confirmed by the HRTEM image of CH3NH3PbBr3 in the EuBTC matrix (b). (c, d) SEM images of EuBTC microcrystals at different magnifications, and the elemental mapping diagrams of Eu (e), N (f), Br (g), and Pb (h) in the CH3NH3PbBr3@EuBTC composite.

Figure 5. (a) Excitation wavelength-dependent emission spectra of CH3NH3PbBr3@EuBTC composites from 254 to 365 nm. (b) Correlation of the emission intensity and the excitation wavelength demonstrating a fitting line. (c) Zoomed in CIE diagram showing that the x (0.590−0.120) and y (0.357−0.573) coordinates upon different excitation wavelengths. (d) Photographs of CH3NH3PbBr3@EuBTC composites encapsulated in the PDMS film irradiated by a UV lamp at 254 and 365 nm, respectively. The decay curves for two different emission centers, 512 nm (e) and 617 nm (f) depending on different excitation wavelengths.

EuBTC MOFs have been formed, and this rod was about 3 μm wide, 5 μm thick, and the length range was about 20 μm. The uniform distribution of Eu, C, and O elements for EuBTC is clearly found from the elemental mapping diagram (Figure 3b−d). Moreover, as shown in Figure 3e, the crystalline morphology of EuBTC possessed similar assembled rod-like microstructures depending on the different amounts of PbBr2 added. Moreover, the uniform distribution of Pb, O, C, Eu, and Br elements in the PbBr2@EuBTC precursor can also be verified by the elemental mapping diagram (Figure 3f−j), which verified that PbBr2 can form the uniform composite with the EuBTC host. Figure 4a shows the TEM image of

from EuBTC into [email protected],45 Figure 2f comparatively shows the pore volume and surface areas of EuBTC and CH3NH3PbBr3@EuBTC, respectively, which were determined to be 0.91 nm and 253.55 m2 g−1 for EuBTC and 0.75 nm and 266.22 m2 g−1 for CH3NH3PbBr3@EuBTC according to the Barrett−Joyner−Halenda (BJH) method. It was found that the pore diameter decreases and the surface area increases after the composite was formed, also suggesting the successful in situ fabrication of the CH3NH3PbBr3 NCs in the pores of EuBTC. Figure 3a shows the typical SEM image of the EuBTC sample synthesized at 120 °C. As can be observed, the rod-like 27879


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Figure 6. (a) Temperature-dependent emission spectra measured at 25−200 °C (λex = 317 nm). (b) Variation of the emission intensity upon 317 nm excitation, with temperature variation for the peaks at 513 nm (CH3NH3PbBr3 NCs) and 617 nm (EuBTC MOFs). (c) Zoomed in CIE diagram showing the variation of the color coordinates depending on temperature (λex = 317 nm). (d) Correlation of the emission intensity and the temperature demonstrating a fitting line.

the maximum at about 513 nm (green emission). When the excitation wavelengths increased from 254 to 365 nm (254, 298, 317, 340, and 365 nm), the emission color of the CH3NH3PbBr3@EuBTC composite would change from red to green, accompanied by a decrease in the red emission peak and an increase in the green emission peak. To quantitatively determine whether the excitation wavelength-dependent color change in luminescence could be used for accurate excitationwavelength detection in anti-counterfeiting applications, we plotted the variation of the emission centers 512/617 nm in the logarithmic luminescence intensity of the CH3NH3PbBr3@ EuBTC composite as a function of excitation wavelength as shown in Figure 5b. A perfect linear relationship related to the luminescence intensity ratio and the excitation wavelength can be observed, which can be fitted to I = 0.02λ − 9.05, where I denotes the ratio of 513 and 617 nm peak intensities, and λ is the wavelength (nm). This linear relationship gives the correlation coefficient (R2) of 0.987, and this value verified that the CH3NH3PbBr3@EuBTC composites can work as a good luminescent wavelength meter in the range of the tested excitation wavelengths ranging from 254 to 365 nm. Figure 5c shows that the corresponding change from red to green luminescence color depending on the excitation wavelength from 254 to 365 nm can be observed in the Commission internationale de l’éclairage (CIE) chromaticity diagram. Meanwhile, the fluorescent photographs were also obtained at 254 (0.590, 0.357), 317 (0.257, 0.500), and 365 nm (0.120, 0.573), respectively. We further make a flower-pattern by mixing the CH3NH3PbBr3@EuBTC composite into a transparent polydimethylsiloxane (PDMS) film to assess their potential applications for anti-counterfeiting labeling. As

CH3NH3PbBr3@EuBTC prepared from the PbBr2@EuBTC precursor and the added CH3NH3Br solution, which revealed the distribution of CH3NH3PbBr3 NCs formed in the EuBTC matrix. Figure 4b shows the HRTEM image of the encapsulated CH3NH3PbBr3 NCs, suggesting that it possesses an interplanar crystal spacing of 3.2 nm, which agrees well with the in-plane lattice spacing of this targeted phase. SEM images of the as-prepared CH3NH3PbBr3@EuBTC composites at different magnifications are shown in Figure 4c,d respectively, which confirms the similar assembled rod-like morphology. Figure 4e−h shows the elemental mapping diagrams of the asprepared CH3NH3PbBr3@EuBTC composites. The result confirms that Pb, Br, N, and Eu elements are equally distributed suggesting the successful formation of the CH3NH3PbBr3@EuBTC composites. Therefore, one can find that the in situ fabrication of the CH3NH3PbBr3 NCs encapsulated into the EuBTC matrix can be realized by such a two-step strategy. Benefiting from the above advantage of in situ fabrication of the CH3NH3PbBr3 perovskite NCs in the EuBTC matrix, the composite is expected to possess multiple photoluminescence anti-counterfeiting technologies. Figure 5 shows the excitation/ emission spectra of the composites and the PDMS film containing CH3NH3PbBr3@EuBTC composites. The emission spectrum consists of a broad range, with well-matched excitation wavelengths ranging from 254 to 365 nm as shown in Figure 5a. When the CH3NH3PbBr3@EuBTC sample was pumped at 254 nm, it yielded strong and sharp emission peaks, which could be ascribed to the electric transitions of Eu3+ ions and resulted in red emission (617 nm). Meanwhile, excitation at 365 nm resulted in a broad band with 27880


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Figure 7. (a) PL spectra and the corresponding digital photos of CH3NH3PbBr3@EuBTC composites during the impregnation-recovery process reacted with water and CH3NH3Br. (b) The variation of emission intensities, peak wavelengths, and FWHM values of the composites during the impregnation-recovery cycles for several cycle numbers. (c) XRD patterns of the composites before and after water immersion, respectively. (d) N2 adsorption isotherms of CH3NH3PbBr3@EuBTC composites before and after water immersion.

shown in Figure 5d, bright red and green fluorescent emissions can be clearly observed as the flower-pattern was excited by 254 and 365 nm UV irradiations, which are ascribed to the characteristic emission of the Eu3+ ion and CH3NH3PbBr3 NC band-edge emission, respectively. We measured the decay curves for the two different emission centers (512 and 617 nm), as shown in Figure 5e,f, respectively, and the lifetime values of the two emission centers are also dependent on the excitation wavelength. The luminescence intensities are dependent on two independent-wavelength excitation sources. It is believed that this unique feature is not easy to be replicated and it represents a kind of advanced anticounterfeiting technology. In general, different luminescent materials can show different thermal stabilities since they should possess various nonradiative relaxation paths. Therefore, it may be a good method for anti-counterfeiting applications, utilizing the ratio of emission colors changing with temperature.46 To verify this, the temperature-dependent luminescence properties of CH3NH3PbBr3@EuBTC composites were investigated as given in Figure 6. PL spectra of the CH3NH3PbBr3@EuBTC composite were recorded over the temperature range of 25− 200 °C upon the excitation at 317 nm, as shown in Figure 6a. With the increase in the temperature, the total luminescence intensities decreased, and the red emission intensity originated from EuBTC was continuously stronger than that of the green emission from CH3NH3PbBr3 NCs at 50 °C. Compared to the rate of change in luminescence intensity between CH3NH3PbBr3 NCs and EuBTC MOFs, with temperature change, the luminescence intensity of CH3NH3PbBr3 NCs normally decreases much more than that of EuBTC, as shown

in Figure 6b. Also, the corresponding color change with temperature from 25 to 200 °C was observed in the CIE diagram shown in Figure 6c. As the luminescence intensity of CH3NH3PbBr3 NCs at 25 °C is slightly higher than EuBTC MOFs at 317 nm, the composite exhibits a green color luminescence. When the temperature changes from 25 to 200 °C, only the red peak can be finally observed. To quantify whether the temperature-dependent color changes of CH3NH3PbBr3@EuBTC composites could be used for accurate temperature detection in anti-counterfeiting applications, one can plot the curve of the luminescence intensity in the logarithmic mode depending on the temperature. Accordingly, Figure 6d gives a very good linear relationship between the luminescence intensity of I513+617/I513 and temperature T (°C), which can be fitted to I = 0.007T − 0.02, where I denotes the emission intensities of I617/I513. The as-calculated correlation coefficient (R2) of 0.947 indicates the excellent linear relationship, which further verified that the CH3NH3PbBr3@EuBTC composites can work as an excellent luminescent thermometer from 25 to 200 °C. In CH3NH3PbBr3@EuBTC system, we properly combine the thermal instability of perovskite CH3NH3PbBr3 NCs and good thermal stability of EuBTC MOFs to exhibit the color variation depending on temperature.38 The unique color change character of the CH3NH3PbBr3@EuBTC composite with temperature from 25 to 200 °C become another method for anti-counterfeiting applications. CH3NH3PbBr3 perovskite NCs is vulnerable and easily destroyed in many hostile conditions. Owing to this particular character, one can also find that the luminescence of the encapsulated CH3NH3PbBr3 member in the EuBTC matrix is 27881


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Figure 8. (a) Reversible fluorescence switching of the USTB pattern written on the paper at different stages and different excitation wavelengths of 254 nm and 365 nm. (b) SEM images of the enlarged paper with different scales of the USTB pattern on the paper.

diameter increases and the surface area decreases slightly with respect to water immersion, which is indicative that the porefilling of the perovskite CH3NH3PbBr3 NCs degraded in the EuBTC matrix. To further present the versatility and applications of the CH3NH3PbBr3@EuBTC composites, the mixed solvent including DMF and ethanol was applied to synthesize the PbBr2@EuBTC precursor solution ink. Then, we personally write the symbol of “USTB” (the abbreviation of the affiliation “University of Science and Technology Beijing”) on a sheet of paper, as shown in Figure 8. Under the excitation of the 365 nm UV lamp, the fluorescent green emission of USTB was quenched quickly by water immersion and appeared again with the addition of CH3NH3Br solution in the composite, which was similar to the powder mentioned above (Figure 8a). As a comparison, even after water immersion, under the 254 nm UV lamp, the red luminescence from the USTB pattern can be clearly observed which is ascribed to the emission of EuBTC MOFs. When the solvent was evaporated, there were some small PbBr2@EuBTC MOF crystals appearing on the paper surface. As shown in Figure 8b, the SEM images of the written USTB pattern, suggests that the USTB pattern contains some microscale CH3NH3PbBr3@EuBTC crystals with the size of nearly 5 μm. Thanks to the excellent optical performance, the CH3NH3PbBr3@EuBTC composite may be used on banknotes for anti-counterfeiting and other emerging practical applications.

quenched depending on water impregnation. PL spectra and the digital photographs of the CH3NH3PbBr3@EuBTC samples are shown in Figure 7a to demonstrate one cycle of the impregnation-recovery process. The as-prepared CH3NH3PbBr3@EuBTC composites exhibit a strong emission peak with the center at 513 nm under 365 nm excitation (curve 1 in Figure 7a). After impregnation with water, the emission of the CH3NH3PbBr3 NCs can be completely quenched. However, the inherent PL emission of EuBTC is still clearly observed (curve 2 in Figure 7a). However, the emission can appear again and the intensity returns to about the original value (curve 3 in Figure 7a) when we mixed the composites after water impregnation with the CH3NH3Br solution again. In the cycle process, the initial color of the asprepared powder is yellow and it changes to white upon immersion into water. Then, the reversion to yellow was accompanied by CH3NH3Br as is also shown in the inset of Figure 7a. Moreover, Figure 7b shows the variation of emission intensities, peak wavelengths, and full width at half-maximum (FWHM) values of the CH3NH3PbBr3@EuBTC composites during the impregnation-recovery cycles for nine cycles, and the stable reversible properties can be observed. Accordingly, the peak positions of the emission intensities remain nearly unchanged, whereas the FWHM values demonstrated the broadening of about 5−9 nm from CH3NH3PbBr3 to the final composite. In this regard, the stable PbBr2@EuBTC precursor plays an important role in the repeated formation of CH3NH3PbBr3@EuBTC composites. Therefore, we compared the XRD patterns and N2 adsorption−desorption isotherms of the CH3NH3PbBr3@EuBTC powder sample after water immersion to clearly show the degradation pathway, as shown in Figure 7c,d. Obviously, the distinct diffraction peaks at 14.9 and 22.5° ascribed to CH3NH3PbBr3 NCs disappeared quickly and changed to PbBr2@EuBTC. Furthermore, The N2 adsorption results verified that that the pore volume and surface areas were 0.752 nm and 266.224 m2 g−1 for the initial CH3NH3PbBr3@EuBTC composite, 0.757 nm and 155.426 m2 g−1 for the as-prepared sample after immersion into water, respectively, based on the BJH method. The pore

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CONCLUSIONS In conclusion, multiple anti-counterfeiting technologies based on the in situ fabrication of perovskite CH3NH3PbBr3 NCs encapsulated in the EuBTC MOF matrix to realize the luminescent CH3NH3PbBr3@EuBTC composites have been successfully developed. Through a two-step synthesis approach, the PbBr2@EuBTC precursor was prepared in the first step, and, then, it reacted with CH3NH3Br to form the CH3NH3PbBr3@Eu-MOF composite with bright emission. The CH3NH3PbBr3@EuBTC composite displays an outstanding excitation wavelength and temperature-dependent 27882


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ACS Applied Materials & Interfaces color transformation and the potential fluorescence mechanisms were elucidated. Additionally, CH3NH3PbBr3@EuBTC can realize controlled quenching and such a reversible luminescence switching can also be achieved between the green and red colors, which was ascribed to the emission of EuBTC MOFs and the CH3NH3PbBr3 NCs, respectively. We believe that our strategy of encapsulated CH3NH3PbBr3 NCs in EuBTC MOFs will open up a potential avenue for designing novel dual-emitting composites with the intriguing luminescent properties of perovskite NCs in anti-counterfeiting applications.

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(10) Wang, W.; Xie, N.; He, L.; Yin, Y. Photocatalytic Colour Switching of Redox Dyes for Ink-Free Light-Printable Rewritable Paper. Nat. Commun. 2014, 5, No. 5459. (11) Liu, J.; Zhuang, Y.; Wang, L.; Zhou, T.; Hirosaki, N.; Xie, R. J. Achieving Multicolor Long-Lived Luminescence in Dye-Encapsulated Metal-Organic Frameworks and Its Application to Anticounterfeiting Stamps. ACS Appl. Mater. Interfaces 2018, 10, 1802−1809. (12) Bao, B.; Li, M.; Li, Y.; Jiang, J.; Gu, Z.; Zhang, X.; Jiang, L.; Song, Y. Patterning Fluorescent Quantum Dot Nanocomposites by Reactive Inkjet Printing. Small 2015, 11, 1649−1654. (13) Li, F.; Wang, X.; Xia, Z.; Pan, C.; Liu, Q. Photoluminescence Tuning in Stretchable PDMS Film Grafted Doped Core/Multishell Quantum Dots for Anticounterfeiting. Adv. Funct. Mater. 2017, 27, No. 1700051. (14) Bai, L.; Xue, N.; Zhao, Y.; Wang, X.; Lu, C.; Shi, W. Dual-Mode Emission of Single-Layered Graphene Quantum Dots in Confined Nanospace: Anti-Counterfeiting and Sensor Applications. Nano Res. 2018, 11, 2034−2045. (15) Lou, Q.; Qu, S.; Jing, P.; Ji, W.; Li, D.; Cao, J.; Zhang, H.; Liu, L.; Zhao, J.; Shen, D. Water-Triggered Luminescent “Nano-Bombs” Based on Supra-(Carbon Canodots). Adv. Mater. 2015, 27, 1389− 1394. (16) Liu, Y.; Ai, K.; Lu, L. Designing Lanthanide-Doped Nanocrystals with Both Up and Down-Conversion Luminescence for AntiCounterfeiting. Nanoscale 2011, 3, 4804−4810. (17) Kang, H.; Lee, J. W.; Nam, Y. Inkjet-Printed Multiwavelength Thermoplasmonic Images for Anticounterfeiting Applications. ACS Appl. Mater. Interfaces 2018, 10, 6764−6771. (18) Zhang, Z.; Chang, H.; Xue, B.; Zhang, S.; Li, X.; Wong, W.-K.; Li, K.; Zhu, X. Near-Infrared and Visible Dual Emissive Transparent Nanopaper Based on Yb(III)−Carbon Quantum Dots Grafted Oxidized Nanofibrillated Cellulose for Anti-Counterfeiting Applications. Cellulose 2017, 25, 377−389. (19) Xuan, T.; Yang, X. F.; Lou, S. Q.; Huang, J. J.; Liu, Y.; Yu, J. B.; Li, H. L.; Wong, K. L.; Wang, C. X.; Wang, J. Highly Stable CsPbBr3 Quantum Dots Coated with Alkyl Phosphate for White LightEmitting Diodes. Nanoscale 2017, 9, 15286−15290. (20) Zhang, F.; Zhong, H. Z.; Chen, C.; Wu, X. G.; Zou, B. S.; Dong, Y. P.; et al. Brightly Luminescent and Color Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology. ACS Nano 2015, 9, 4533−4542. (21) Lee, S.; Park, J. H.; Nam, Y. S.; Lee, B. R.; Zhao, B.; Di Nuzzo, D.; Jung, E. D.; Jeon, H.; Kim, J. Y.; Jeong, H. Y.; Friend, R. H.; Song, M. H. Growth of Nanosized Single Crystals for Efficient Perovskite Light-Emitting Diodes. ACS Nano 2018, 12, 3417−3423. (22) Huang, H.; Susha, A. S.; Kershaw, S. V.; Hung, T. F.; Rogach, A. L. Control of Emission Color of High Quantum Yield CH3NH3PbBr3 Perovskite Quantum Dots by Precipitation Temperature. Adv. Sci. 2015, 2, No. 1500194. (23) Droseros, N.; Longo, G.; Brauer, J. C.; Sessolo, M.; Bolink, H. J.; Banerji, N. Origin of The Enhanced Photoluminescence Quantum Yield in MAPbBr3 Perovskite with Reduced Crystal Size. ACS Energy Lett. 2018, 3, 1458−1466. (24) Huang, S.; Li, Z.; Kong, L.; Zhu, N.; Shan, A.; Li, L. Enhancing the Stability of CH3NH3PbBr3 Quantum Dots by Embedding in Silica Spheres Derived from Tetramethyl orthosilicate in “Waterless” Toluene. J. Am. Chem. Soc. 2016, 138, 5749−5752. (25) Niu, G.; Guo, X.; Wang, L. Review of Recent Progress in Chemical Stability of Perovskite Solar Cells. J. Mater. Chem. A 2015, 3, 8970−8980. (26) Zhang, C.; Wang, B.; Li, W.; Huang, S.; Kong, L.; Li, Z.; Li, L. Conversion of Invisible Metal-Organic Frameworks to Luminescent Perovskite Nanocrystals for Confidential Information Encryption and Decryption. Nat. Commun. 2017, 8, No. 1138. (27) Zhou, H. C.; Long, J. R.; Yaghi, O. M. Introduction to MetalOrganic Frameworks. Chem. Rev. 2012, 112, 673−674. (28) Park, J.; Wang, Z. U.; Sun, L. B.; Chen, Y. P.; Zhou, H. C. Introduction of Functionalized Mesopores to Metal-Organic Frame-

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Quanlin Liu: 0000-0003-3533-7140 Zhiguo Xia: 0000-0002-9670-3223 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (No. 51722202, 91622125, and 51572023), the Natural Science Foundations of Beijing (2172036), and the Open Research Fund Program of Key Laboratory of Cosmetic (Beijing Technology and Business University), China National Light Industry.

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REFERENCES

(1) Yoon, B.; Lee, J.; Park, I. S.; Jeon, S.; Lee, J.; Kim, J. M. Recent Functional Material Based Approaches to Prevent and Detect Counterfeiting. J. Mater. Chem. C 2013, 1, 2388−2403. (2) Kumar, P.; Singh, S.; Gupta, B. K. Future Prospects of Luminescent Nanomaterial Based Security Inks: From Synthesis to Anti-Counterfeiting Applications. Nanoscale 2016, 8, 14297−14340. (3) Wu, Y.; Zhong, Y.; Chu, B.; Sun, B.; Song, B.; Wu, S.; Su, Y.; He, Y. Plant-Derived Fluorescent Silicon Nanoparticles Featuring Excitation Wavelength-Dependent Fluorescence Spectra for AntiCounterfeiting Applications. Chem. Commun. 2016, 52, 7047−7050. (4) Jiang, K.; Zhang, L.; Lu, J.; Xu, C.; Cai, C.; Lin, H. Triple-Mode Emission of Carbon Dots: Applications for Advanced Anti-Counterfeiting. Angew. Chem., Int. Ed. 2016, 55, 7231−7235. (5) Sun, T.; Xu, B.; Chen, B.; Chen, X.; Li, M.; Shi, P.; Wang, F. Anti-counterfeiting Patterns Encrypted with Multi-Mode Luminescent Nanotaggants. Nanoscale 2017, 9, 2701−2705. (6) Kumar, P.; Dwivedi, J.; Gupta, B. K. Highly Luminescent Dual Mode Rare-earth Nanorod Assisted Multi-Stage Excitable Security Ink for Anti-Counterfeiting Applications. J. Mater. Chem. C 2014, 2, 10468−10475. (7) Kumar, P.; Nagpal, K.; Gupta, B. K. Unclonable Security Codes Designed from Multicolor Luminescent Lanthanide-Doped Y2O3 Nanorods for Anticounterfeiting. ACS Appl. Mater. Interfaces 2017, 9, 14301−14308. (8) Zhang, K. Y.; Chen, X.; Sun, G.; Zhang, T.; Liu, S.; Zhao, Q.; Huang, W. Utilization of Electrochromically Luminescent TransitionMetal Complexes for Erasable Information Recording and Temperature-Related Information Protection. Adv. Mater. 2016, 28, 7137− 7142. (9) Jiang, Y.; Li, G.; Che, W.; Liu, Y.; Xu, B.; Shan, G.; Zhu, D.; Su, Z.; Bryce, M. R. A Neutral Dinuclear Ir(iii) Complex for AntiCounterfeiting and Data Encryption. Chem. Commun. 2017, 53, 3022−3025. 27883


Research Article

ACS Applied Materials & Interfaces works via Metal-Ligand-Fragment Coassembly. J. Am. Chem. Soc. 2012, 134, 20110−20116. (29) Li, M.; Li, D.; O’Keeffe, M.; Yaghi, O. M. Topological Analysis of Metal-Organic Frameworks with Polytopic Linkers and/or Multiple Building Units and the Minimal Transitivity Principle. Chem. Rev. 2014, 114, 1343−1370. (30) Rösler, C.; Fischer, R. A. Metal−Organic Frameworks as Hosts for Nanoparticles. CrystEngComm 2015, 17, 199−217. (31) Cui, Y.; Li, B.; He, H.; Zhou, W.; Chen, B.; Qian, G. MetalOrganic Frameworks as Platforms for Functional Materials. Acc. Chem. Res. 2016, 49, 483−493. (32) Dong, Y.; Cai, J.; Fang, Q.; You, X.; Chi, Y. Dual-Emission of Lanthanide Metal-Organic Frameworks Encapsulating Carbon-Based Dots for Ratiometric Detection of Water in Organic Solvents. Anal. Chem. 2016, 88, 1748−1752. (33) Kaur, R.; Vellingiri, K.; Kim, K. H.; Paul, A. K.; Deep, A. Efficient Photocatalytic Degradation of Rhodamine 6G with a Quantum Dot-Metal Organic Framework Nanocomposite. Chemosphere 2016, 154, 620−627. (34) Xia, T.; Song, T.; Cui, Y.; Yang, Y.; Qian, G. A Dye Encapsulated Terbium-Based Metal-Organic Framework for Ratiometric Temperature Sensing. Dalton Trans. 2016, 45, 18689−18695. (35) Xu, G. W.; Wu, Y. P.; Dong, W. W.; Zhao, J.; Wu, X. Q.; Li, D. S.; Zhang, Q. A Multifunctional Tb-MOF for Highly Discriminative Sensing of Eu3+/Dy3+ and as a Catalyst Support of Ag Nanoparticles. Small 2017, 13, No. 1602996. (36) Gu, Z. G.; Zhang, J. Epitaxial Growth and Applications of Oriented Metal−Organic Framework Thin Films. Coord. Chem. Rev. 2017, DOI: 10.1016/j.ccr.2017.09.028. (37) Kaczmarek, A. M.; Liu, Y.-Y.; Wang, C.; Laforce, B.; Vincze, L.; Van Der Voort, P.; Van Hecke, K.; Van Deun, R. Lanthanide “Chameleon” Multistage Anti-Counterfeit Materials. Adv. Funct. Mater. 2017, 27, No. 1700258. (38) Xu, B.; Guo, H.; Wang, S.; Li, Y.; Zhang, H.; Liu, C. Solvothermal Synthesis of Luminescent Eu(BTC)(H2O)DMF Hierarchical Architectures. CrystEngComm 2012, 14, 2914−2919. (39) Zhang, D.; Xu, Y.; Liu, Q.; Xia, Z. Encapsulation of CH3NH3PbBr3 Perovskite Quantum Dots in MOF-5 Microcrystals as a Stable Platform for Temperature and Aqueous Heavy Metal Ion Detection. Inorg. Chem. 2018, 57, 4613−4619. (40) Zhang, J.; Zeng, J.; Liu, Y.; Sun, L. X.; You, W. S.; Sawada, Y.; et al. Thermal Decomposition Kinetics of the Synthetic Complex Pb(1,4-BDC)(DMF)(H2O). J. Therm. Anal. Calorim. 2008, 91, 189− 193. (41) Chen, D.; Shen, W.; Wu, S.; Chen, C.; Luo, X.; Guo, L. Ion Exchange Induced Removal of Pb(ii) by MOF-Derived Magnetic Inorganic Sorbents. Nanoscale 2016, 8, 7172−7179. (42) Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V. Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut. Nano Lett. 2015, 15, 3692−3696. (43) Fang, X.; Zhai, W.; Zhang, K.; Wang, Y.; Yao, L.; Tian, C.; Wan, Y.; Hou, R.; Li, Y.; Chen, W.; Ran, G. Wide Range Tuning of the Size and Emission Color of CH3NH3PbBr3 Quantum Dots by Surface Ligands. AIP Adv. 2017, 7, No. 085217. (44) Medina-Velazquez, D. Y.; Alejandre-Zuniga, B. Y.; Loera-Serna, S.; Ortiz, E. M.; Morales-Ramirez, A. D. J.; Garfias-Garcia, E.; GarciaMurillo, A.; Falcony, C. An Alkaline One-Pot Reaction to Synthesize Luminescent Eu-BTC MOF Nanorods, Highly Pure and WaterInsoluble, under Room Conditions. J. Nanopart. Res. 2016, 18, No. 352. (45) Wang, S.; Huang, F.; Zhou, L.; Wei, J.; Xin, Y.; Jin, P.; Cai, Z.; Yin, Z.; Pang, Q.; Zhang, J. Z. Enhanced Photoluminescence and Stability of CH3NH3PbBr3 Perovskite Nanocrystals with Protonated Melamine. ChemNanoMat 2018, 4, 409−416. (46) Xu, L.; Chen, J.; Song, J.; Li, J.; Xue, J.; Dong, Y.; Cai, B.; Shan, Q.; Han, B.; Zeng, H. Double-Protected All-Inorganic Perovskite Nanocrystals by Crystalline Matrix and Silica for Triple-Modal Anti-

Counterfeiting Codes. ACS Appl. Mater. Interfaces 2017, 9, 26556− 26564.

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CH3NH3PbBr3 Perovskite Nanocrystals Encapsulated in Lanthanide

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