Surface Patterning Of Persistent Luminescent Hybrids Linked With Coordination Bond And Its Application

In recent years,the surface coating technology of rare-earth activated persistent phosphors has been widely studied and used due to its prominent advantage in materials modification and addition new function, especially organic-inorganic hybrid materials linked with chemical bond have been received great interest due to its combination the advantages of both organic and inorganic components. In this study, four different types of organic-inorganic long afterglow hybrid phosphors with raspberry-like were patterned with SrAl2O4:Eu2+,Dy3+（SAO-ED） phosphor as core materials and poly methyl methacrylate （PMMA）, maleic anhydride （MA）, spiropyrans（SP） as coating materials, respectively. The correlation between structure and performances of those phosphors was studied, and the interaction between organic and inorganic components were emphasized, and their application in waterborne coatings was investigated.The hydrolysis behavior of SAO-ED phosphor at room temperature in water solution and moisture environment were studied. X-ray diffraction （XRD） and X-ray photoelectron spectra （XPS） data showed two different compound were formed when SAO-ED phosphor reacted with water, which changed the crystal structure of SAO-ED, elevate pH value and electric conductivity of water solution. In comparison with the un-hydrolyzed SAO-ED, there were changes in the intensity of photoluminescence （PL）, the peak position of the emission spectrum and afterglow decay.PMMA/SAO-ED hybrid phosphor were prepared with crylic acid （AA） as an organic ligand directly coated on SAO-ED phosphors by the interfacial coordination method, then MMA monomer in-situ polymerization on the surface by the solution polymerization method. The effect of coating process conditions on the properties of hybrid phosphors was investigated. Under the optimum in-situ polymerization condition, the conversion of MMA was 44.6% and the grafting ratio of PMMA was 10.9%. In contrast with SAO-ED phosphor, PMMA coating layer can effectively improve the water resistance of SAO-ED phosphors, and the pH value of PMMA/SAO-ED hybrid phosphor water solution was kept 7.0 for a long time, and the PL intensity and afterglow life were kept 92.3% and 94.1%, respectively. Fourier transform infrared spectroscopy （FTIR） and XPS analysis showed the dense PMMA coating layer was consisted of AA coordination with metal ions on the surface of SAO-ED phosphors and the vinyl group C=C polymerization with MMA in-situ. Scanning electron microscopy （SEM） photographs showed PMMA/SAO-ED hybrid phosphors was raspberry-like structure, and the bulk of PMMA particle was 1μm.MA/SAO-ED hybrid phosphor was prepared by the interfacial coordination chemistry method and using MA as an organic ligand and directly coating on the surface of SAO-ED phosphors. The key coating factors: such as solvent, MA concentration, reactive temperature, pH value of solution and reactive time, were determined by the growth unit theory of coordination polyhedrons. The effect of these parameters on the structure and properties of hybrid phosphors was investigated. Under the optimum coating condition, the homogenous and compact MA coating layer was aptly formed, and the coverage of MA was 7.69%. FTIR and XPS data showed hydrolysis production of MA was adsorbed chemically on the surface of the SAO-ED phosphors by the coordination bond M ? O→C and O→M （primarily the former）, the following maleic acid further was adsorbed by bridging O atom so that a layer of continuous and dense coating film came into being. XRD analysis showed the coating process didn’t destroy the crystal structure of the phosphors. It was also found that the introducing of MA didn’t change the excitation and emission spectra of SAO-ED phosphors, but decreased the luminous intensity, which was verified by the PL measurement, and the PL intensity and afterglow life was less 3% and 3.5% than that of uncoated SAO-ED phosphor. MA coating layer can effectively prevent the hydrolysis of SAO-ED phosphor, and pH value of MA/SAO-ED hybrid phosphor was kept 7.0 for a long time. Real-time TG-DSC was used to monitor the coating kinetics process, indicating the coordination coating process was controlled through diffusion, and the activation energy was 15.48 kJ·mol^-1.Two kinds of SP were synthesized, and their photochromic properties and light fatigue were also discussed. SP/SAO-ED hybrid phosphors were prepared with SP as coating materials and SAO-ED phosphor as coated materials. FTIR and XPS data showed heterocyclic N atom of SP was coordinated with metal ions on the surface of SAO-ED phosphors. The hybrid phosphors combined the advantages of PL property of SAO-ED phosphor and photochromic property of SP, and its ring-closing reaction rate constant was less than that of SP, and color showing time and light fatigue was longer than that of SP.On the basis of MA and SP alone coating, （MA+SP）/SAO-ED hybrid phosphor was prepared with MA and SP as composite coating materials. Under the total 10% coverage, The effect of mass ratio and coating order of MA and SP on the properties of hybrid phosphor was investigated.The waterborne luminescent coatings were manufactured by using the hybrid phosphors as pigments and the acrylic latex modified with silicone as the binder, and the performances of the coatings were studied. The results showed the pigment/binder ratio, the thickness of coating film and surface modification of SAO-ED phosphor played important roles on mechanic performances, persistent luminescence and water resistance of coating film.