| A wide range of rare-earth phosphors have been used widely in many fields such as anti-counterfeiting, lighting, display, scintillator, X-ray imaging, etc. The application of rare-earth phosphors in anti-counterfeiting is mainly anti-counterfeiting ink, anti-counterfeiting stamp ink, etc. The rare-earth phosphors mostly are organic complexes of rare-earths, which are synthesized with high energy consumption, and the luminous purity and luminous efficiency are not better. Meanwhile, the anti-counterfeiting technology is improved gradually, so it is very important to develop the low energy consumption and full-color phosphor. However, there are very few reports on the application of inorganic rare-earth fluorescent materials in anti-counterfeiting. Calcium carbonate as the host of inorganic powder has many merits, for example, inexpensive and can be used as polymer filler to reduce the addition of polymer and reinforce properties. In addition, compared to organic rare-earth complexes, the preparation method of calcium carbonate is also simpler. Our team has made some research on the calcium carbonate phosphor. If by mixing the red, green and blue phosphors to realize the full-color, these problems of color resorption, difficult to control the ratio and chemical stability will affect the color reduction and stability. Therefore, it is very important to develop a panchromatic and single substrate calcium carbonate based tunable phosphor.In this paper, a series of calcium carbonate based tunable phosphors were prepared by microwave co-precipitation method and polylactic acid fluorescent films (PLA/CaCO3:RE13+,RE23+) were prepared by solvent evaporation method. Calcium nitrate, rare-earth nitrate (including Eu, Tb, Dy, Ce, etc.) and sodium carbonate were used as raw materials. Effects of molar concentration ratio, wavelength and charge compensation on properties of tunable phosphors were investigated by X-ray diffraction pattern (XRD), scanning electron micrograph (SEM), laser particle size analyzer, differential thermal analysis (TG-SDTA) and fluorescence spectroscopy (PL-PLE). In addition, the application in polylactic acid was discussed preliminarily. The results showed that:(1) As the change of rare-earth ions molar concentration and excitation wavelength, the emission of CaCO3:Eu3+,Dy3+phosphors changed over a wide range of red, blue and green color, and CaCO3:Eu3+,Tb3+phosphors emitted light between red and green. But the emission of CaCO3:Ce3+,Tb3+phosphors shifted from blue to green color.(2) In these rare-earth co-doped calcium carbonate based phosphors, Dy3+, Tb3+and Ce3+ions were not only activators, also played the role of sensitizing agent. Among them, the energy transfer occurred from Dy3+and Tb3+ions to Eu3+ions, and from Ce3+ions to Tb3+ions.(3) Within a certain range, the doping of Li+ions did not change the crystal structure of CaCO3, and played the role of charge compensation in the tunable rare-earth doped calcium carbonate phosphors. The emission intensity of the phosphor was improved to some extent with the doping of Li+ions.(4) The tunable phosphor could be evenly distributed in the polylactic acid film, and there was little agglomerate phenomenon. Compared with pure polylactic acid film, the decomposition temperature and the thermal stability of fluorescent films added CaCO3:RE13+, RE23+phosphors was reduced. The emission peaks of fluorescent films were consistent with the corresponding tunable phosphor. In addition, The Commission Internationale De Eclairage (CIE) chromaticity coordinates of these fluorescent films were different when the added phosphors were different. Therefore, the prepared tunable phosphor can be used to prepare polylactic acid films which show different colors under a certain source and can be applied to fluorescent anti-counterfeiting and display devices, etc. |
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