Synthesis and Application in Anticounterfeiting of RGB Upconversion Nanoparticles

Zhang, Yongling; Lv, Peng; Qin, Zhengkun

doi:https://doi.org/10.1155/2019/3872591

Journal of Nanomaterials

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Abstract Introduction Experimental Results and Discussion Conclusion Data Availability Conflicts of Interest Acknowledgments Supplementary Materials References Copyright Related Articles

Research Article | Open Access

Volume 2019 | Article ID 3872591 | https://doi.org/10.1155/2019/3872591

Synthesis and Application in Anticounterfeiting of RGB Upconversion Nanoparticles

Yongling Zhang,¹Peng Lv,¹and Zhengkun Qin¹

Academic Editor: Domenico Acierno

Received18 Aug 2019

Accepted30 Nov 2019

Published20 Dec 2019

Abstract

In this paper, we synthesized nm cubic phase KMnF₃:Yb³⁺,Er³⁺ NPs, nm hexagonal phase NaYF₄:Yb³⁺,Tm³⁺ NPs, and nm hexagonal phase NaYF₄:Yb³⁺,Er³⁺ NPs. Under the excitation of 980 nm, the strong red upconversion luminescence (⁴F_9/2⟶⁴I_15/2, the peak is located at ~653 nm) of Er³⁺ ions of KMnF₃:Yb³⁺,Er³⁺ NPs can be seen, the strong blue upconversion luminescence (¹D₂⟶³F₄, ¹G₄⟶³H₆; the peaks are located at ~451 nm and ~477 nm, respectively) of Tm³⁺ ions of NaYF₄:Yb³⁺,Tm³⁺ NPs can be observed, and the strong green upconversion luminescence (⁴I_11/2⟶⁴I_15/2, ⁴S_3/2⟶⁴I_15/2; the peaks are located at ~524 nm and ~541 nm, respectively) of Er³⁺ ions of NaYF₄:Yb³⁺,Er³⁺ NPs can be found. The mixed white upconversion luminescent materials can be obtained by adjusting the doping ratio of the above NPs. Cyclohexane solution of red, blue, green, and the mixed white NPs can be used as ink, and “JLNU” is written on paper with a pen. Without 980 nm radiation, nothing could be seen. Under 980 nm irradiation, the colored letters “JLNU” can be seen. Red, blue, green, and the mixed white upconversion NPs can be used in security anticounterfeiting.

1. Introduction

Lanthanide-doped nanoparticles (NPs) have been widely used in many fields due to sharp emission peaks, stable chemical properties, and a long fluorescence lifetime, such as optical waveguide amplifiers, biomarkers, bioimaging, and three-dimensional display [1–7]. In recent years, lanthanide-doped NPs have shown great application prospects in anticounterfeiting applications [8–10]. Li et al. [11] synthesized NaGdF₄:Yb,Er@NaYF₄:Yb@NaGdF₄:Yb,Nd@NaYF₄@NaGdF₄:Yb,Tm@NaYF₄ NPs by high temperature thermal decomposition. Excited at 980 nm, the prepared NPs show ultraviolet and blue upconversion luminescence coming from Tm³⁺ ions. Under the excitation of 796 nm, the prepared NPs show green and red upconversion luminescence coming from Er³⁺ ions. The multishell NPs can be applied to dual anticounterfeiting security design. Lei et al. [12] prepared Na₃ZrF₇:Yb,Er NPs and Na₃ZrF₇:Yb,Ho NPs. Under the excitation of 980 nm, these NPs can display upconversion luminescence of Er³⁺ and Ho³⁺ ions, which can be applied to security anticounterfeiting. Han et al. [13] fabricated NaYF₄:2%Er,0.5%Tm@NaYF₄ core-shell NPs, and the prepared NPs show different fluorescent colors by controlling the pulse duration and repetition frequency of the pump light. This optical property of NaYF₄:2%Er,0.5%Tm@NaYF₄ core-shell NPs can be applied to antifake printing. Based on the application of lanthanide-doped NPs in anticounterfeiting, we have done the following research work. In our work, cubic KMnF₃:18%Yb³⁺,1%Er³⁺ NPs, hexagonal NaYF₄:18%Yb³⁺,0.5%Tm³⁺ NPs, and hexagonal NaYF₄:18%Yb³⁺,2%Er³⁺ NPs with oleic acid functional groups on the surface were successfully fabricated. We characterize the crystalline phases (XRD) and morphologies (SEM) of the three NPs. Meanwhile, we also monitored the fluorescence spectra of the three NPs under 980 nm excitation. Interestingly, we obtained the mixed white NPs by adjusting the doping ratio of the three NPs. The fluorescence spectra of white NPs stimulated by 980 nm can be obtained. These four NPs, which emit upconversion luminescence of red, blue, green, and mixed white, can be applied to anticounterfeiting.

2. Experimental

2.1. Preparation of Red, Blue, and Green Nanoparticles

The preparation process of red upconversion KMnF₃:Yb³⁺,Er³⁺ NPs is shown as follows: oleic acid, ethanol, and deionized water were poured into 50 ml beakers as reaction solvents with volumes of 10 ml, 5 ml, and 5 ml, respectively. 12 mmol KOH was poured into the aforementioned beaker, and the reaction solution was stirred for half an hour. Next, YbCl₃·6H₂O, ErCl₃·6H₂O, and MnCl₂ with moles of 0.072 mmol, 0.008 mmol, and 0.32 mmol, respectively, were poured into the aforementioned beaker in sequence. Then, the reaction solution was stirred for another half an hour. 3.5 mmol KF was poured into the aforementioned beaker under stirring conditions. Finally, all the solutions in the beaker were placed in the hydrothermal reactor and kept at 200 degrees for 12 hours. The reaction product was centrifugally washed with a mixture of ethanol and cyclohexane [14, 15].

The preparation process of blue upconversion NaYF₄:Yb³⁺,Tm³⁺ NPs and green upconversion NaYF₄:Yb³⁺,Er³⁺ NPs is the same. The specific preparation process is shown below: 4 ml oleic acid, 6 ml octadecene, and 0.4 mmol ReCl₃·6H₂O were poured into a 50 ml two-necked flask with round bottom and kept at 150 degrees for an hour with stirring. Argon needed to be introduced into the reaction system. After the reaction solution was cooled, 8 ml methanol solution containing 1 mmol NaOH and 1.2 mmol NH₄F was poured into the aforementioned round bottom. The reaction system was stirred for half an hour. And the temperature of the reaction solution was raised to 50 degrees with stirring. In this process, argon was needed to flow into the atmosphere. Finally, the reaction solution was heated to 300 degrees and kept an hour with stirring. Argon was needed to flow into the atmosphere. The reaction product was centrifugally washed with a mixture of ethanol and cyclohexane [16, 17].

2.2. Characterizations

The X-ray powder diffraction (XRD) of red, blue, and green NPs was achieved via Rigaku RU-200B ( Å, scanning range: 10°-70°). The scanning electron microscope (SEM) of red, blue, and green NPs was obtained through JSM-7500F, JEOL, Japan. All upconversion spectra in this paper were collected via the Hitachi F-4500 fluorescence spectrophotometer. All color photographs of this paper were taken by Nikon D3200.

3. Results and Discussion

The solvothermal strategy was used to synthesize KMnF₃:18%Yb³⁺,1%Er³⁺ NPs, and the detailed synthesis steps of KMnF₃:Yb³⁺,Er³⁺ NPs have been given in the experimental part (Section 2.1). Figure 1 displayed the XRD and SEM of KMnF₃:Yb³⁺,Er³⁺ NPs. From the analysis of the results, synthetic KMnF₃:Yb³⁺,Er³⁺ NPs are cubic KMnF₃ crystals, because all diffraction peaks of synthetic KMnF₃:Yb³⁺,Er³⁺ NPs and the cubic KMnF₃ standard card (JCPDS: 82-1334) are in the same position (Figure 1(a)). The synthetic KMnF₃:Yb³⁺,Er³⁺ NPs could be assigned a cubic structure, and its size is nm (Figure 1(b)). The high temperature thermal decomposition strategy was adopted to prepare NaYF₄:18%Yb³⁺,0.5%Tm³⁺ NPs, and the operation steps of the experiment were introduced in the experimental part (Section 2.1). Figure 2 exhibits the XRD and SEM of NaYF₄:Yb³⁺,Tm³⁺ NPs. As can be seen from Figure 2(a), the prepared NaYF₄:Yb³⁺,Tm³⁺ NPs could be assigned a hexagonal structure. That is because the positions of all diffraction peaks of NaYF₄:Yb³⁺,Tm³⁺ NPs and the hexagonal NaYF₄ standard card (JCPDS: 28-1192) are identical. Besides, the morphology of NaYF₄:Yb³⁺,Tm³⁺ NPs is hexagonal, and its size is nm (Figure 2(b)). The synthesis process of NaYF₄:18%Yb³⁺,2%Er³⁺ NPs is the same as that of NaYF₄:Yb³⁺,Tm³⁺ NPs. Figure 3 shows the XRD and SEM of NaYF₄:18%Yb³⁺,2%Er³⁺ NPs. It has been found from Figure 3(a) that the position of the diffraction peak of NaYF₄:Yb³⁺,Er³⁺ NPs is exactly the same as that of the hexagonal NaYF₄ standard card (JCPDS: 28-1192), hereby certifying that the prepared NaYF₄:Yb³⁺,Er³⁺ NPs could be assigned a hexagonal structure. Another conclusion can be drawn from Figure 3(b) that NaYF₄:Yb³⁺,Er³⁺ NPs are nm.

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Upconversion fluorescence spectra of KMnF₃:18%Yb³⁺,1%Er³⁺ NPs, NaYF₄:18%Yb³⁺,0.5%Tm³⁺ NPs, and NaYF₄:18%Yb³⁺,2%Er³⁺ NPs excited by 980 nm are shown in Figures 4(a)–4(c). The fluorescence photographs of the corresponding NP cyclohexane solution are embedded in each figure. Figure 4(d) displays the CIE color coordinates of the corresponding NPs excited by 980 nm. In the fluorescence spectra of KMnF₃:18%Yb³⁺,1%Er³⁺ NPs, an emission peak at ~653 nm can be clearly seen as a result of ⁴F_9/2⟶⁴I_15/2 radiation transition, which is due to the existence of efficient energy transfer between Er³⁺ and Mn²⁺: ²H_11/2, ⁴S_3/2+⁶A₁⟶⁴I_15/2+⁴T₁, ²H_9/2+⁶A₁⟶⁴I_13/2+⁴T₁, and ⁴I_15/2+⁴T₁⟶⁴F_9/2+⁶A₁ [14, 15] (the energy-level diagram of KMnF₃:Yb³⁺,Er³⁺ NPs excited with a 980 nm laser is shown in Figure S1). Therefore, KMnF₃:Yb³⁺,Er³⁺ NPs can emit red fluorescence, which can be demonstrated by digital photos and the CIE color coordinates of KMnF₃:Yb³⁺,Er³⁺ NPs. From Figure 4(b), it appears that NaYF₄:Yb³⁺,Tm³⁺ NPs have three emission peaks: a strong emission peak at 477 nm (¹G₄⟶³H₆) and two weak emission peaks at 451 nm (¹D₂⟶³F₄) and 644 nm (³F₃⟶³H₆). All emission peaks come from radiation transition of Tm³⁺ ions in NaYF₄:Yb³⁺,Tm³⁺ NPs (the energy-level diagram of NaYF₄:Yb³⁺,Tm³⁺ NPs excited with a 980 nm laser is shown in Figure S2). Compared with the fluorescence emission intensity at 477 nm, the emission at 451 and 644 nm can be neglected, so NaYF₄:Yb³⁺,Tm³⁺ NPs show blue fluorescence emission, which can be seen from the photographs and the CIE color coordinates of NaYF₄:Yb³⁺,Tm³⁺ NPs. As you can see in Figure 4(c), in the fluorescence spectra of NaYF₄:Yb³⁺,Er³⁺ NPs, a strong green upconversion emission peak (~541 nm) can be seen, which is attributed to the energy-level transition process of ⁴S_3/2⟶⁴I_15/2. Three weak upconversion emission peaks (~524 nm, ~410 nm, and ~657 nm) can be seen, which are attributed to the energy-level transition process of ⁴I_11/2⟶⁴I_15/2, ²H_9/2⟶⁴I_15/2, and ⁴F_9/2⟶⁴I_15/2 (the energy-level diagram of NaYF₄:Yb³⁺,Er³⁺ NPs excited with a 980 nm laser is shown in Figure S3). Because these three emission peaks are too weak, the fluorescence color of NaYF₄:Yb³⁺,Er³⁺ NPs show a green upconversion fluorescence. It can be proven in the digital photos and the CIE color coordinates of NaYF₄:Yb³⁺,Er³⁺ NPs.

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In the following experiments, we first mixed KMnF₃:Yb³⁺,Er³⁺ NPs, NaYF₄:Yb³⁺,Tm³⁺ NPs, and NaYF₄:Yb³⁺,Er³⁺ NPs in the mass ratio of 42 : 54 : 4, respectively, and then dissolved the mixed NPs into cyclohexane. Under 980 nm irradiation, the mixed NPs can emit white upconversion luminescence; the fluorescence spectra are shown in Figure 5(a). Three distinct emission peaks can be observed in Figure 5(a); comparing with Figure 4, we can see that the first fluorescent emission is from Tm³⁺ ions of NaYF₄:Yb³⁺,Tm³⁺ NPs with wavelengths ranging from 446 nm to 494 nm, the second fluorescent emission comes from Er³⁺ ions of NaYF₄:Yb³⁺,Er³⁺ NPs with wavelengths ranging from 515 nm to 564 nm, and the third fluorescent emission is from Er³⁺ ions of KMnF₃:Yb³⁺,Er³⁺ NPs with wavelengths ranging from 632 nm to 681 nm. Mixed NPs exhibit white upconversion luminescence, which can be demonstrated by photographs of mixed NPs and the CIE color coordinates of mixed NPs under 980 nm irradiation.

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Interestingly enough, we dissolve red KMnF₃:Yb³⁺,Er³⁺ NPs, blue NaYF₄:Yb³⁺,Tm³⁺ NPs, green NaYF₄:Yb³⁺,Er³⁺ NPs, and the mixed white NPs (mixing of KMnF₃:Yb³⁺,Er³⁺ NPs, NaYF₄:Yb³⁺,Tm³⁺ NPs, and NaYF₄:Yb³⁺,Er³⁺ NPs with a mass percentage of 42%, 54%, and 4%, respectively) into the cyclohexane as ink and write directly on the paper with this ink. Without 980 nm laser irradiation, no pattern or text can be seen on the paper. Under 980 nm laser irradiation, four letters of “J,” “L,” “N,” and “U” will appear on the paper, which are written using our own synthetic red, green, blue, and white ink. Under 980 nm laser excitation, the photographs are shown in Figures 6(a)–6(d). Furthermore, green upconversion NPs were used as ink for writing the letters “JLNU.” Under 980 nm irradiation, we can clearly see the letters “JLNU” appear on paper, as shown in Figure 6(e). Significantly, these four nanoparticles can be used in anticounterfeiting.

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4. Conclusion

We prepared KMnF₃:18%Yb³⁺,1%Er³⁺ NPs, NaYF₄:18%Yb³⁺,0.5%Tm³⁺ NPs, and NaYF₄:18%Yb³⁺,2%Er³⁺ NPs encapsulated by oleic acid ligands. Under 980 nm excitation, KMnF₃:Yb³⁺,Er³⁺ NPs can emit strong red upconversion luminescence which comes from ⁴F_9/2⟶⁴I_15/2 radiation transition, NaYF₄:Yb³⁺,Tm³⁺ NPs can send strong blue upconversion emission which comes from ¹G₄⟶³H₆ radiation transition, and NaYF₄:Yb³⁺,Er³⁺ NPs can give strong green upconversion emission which comes from ⁴S_3/2⟶⁴I_15/2 radiation transition. Then, the white upconversion NPs can be obtained by mixing the three NPs. These NPs are used as fluorescent anticounterfeiting materials in product safety design.

Data Availability

All data are obtained through our own experiments. The public database is not used in this article. If the reader needs the data in this article, he can contact the authors ([email protected]).

Conflicts of Interest

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

This work was supported by (1) the Science and Technology Development Plan Project of Jilin Province of China (No. 1: 20180520199JH, No. 2: 20180520191JH), (2) the Science and Technology Project of the Jilin Provincial Education Department of China (No. 1: JJKH20180762KJ, No. 2: JJKH20191006KJ), and (3) the National Natural Science Foundation of China (No. 21701047).

Supplementary Materials

Figure S1: the energy-level diagram of KMnF₃:Yb³⁺,Er³⁺ NPs excited with a 980 nm laser. Figure S2: the energy-level diagram of NaYF₄:Yb³⁺,Tm³⁺ NPs excited with a 980 nm laser. Figure S3: the energy-level diagram of NaYF₄:Yb³⁺,Er³⁺ NPs excited with a 980 nm laser. (Supplementary Materials)

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Copyright

Copyright © 2019 Yongling Zhang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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