Water-based luminescent powder is modified by silica cladding on SrAl2O4: Eu2+ and Dy3+ long afterglow luminescent powder by chemical precipitation method, which can effectively improve the water resistance of luminescent powder, but has little effect on the long afterglow luminescence characteristics of luminescent powder. Emulsion paint with modified luminescent powder has the advantages of storage stability and good water resistance. Luminescence performance before and after modification of luminescent powder: the peak types and peak positions of the excitation and emission spectra of the samples before and after coating were almost identical, with one emission peak at 515nm and multiple excitation spectra at 252nm, 318nm, 369nm and 420nm, which were all generated by 4f7-4f65d1 of Eu2+ outer electrons. Similar excitation and emission spectra further indicated that the crystal structure of the coated luminescent powder did not change, and the lattice environment of Eu2+ was the same as that before the coating. However, the intensity of excitation and emission peaks decreased after the coating, indicating that the existence of the coating layer (due to its reflection, scattering and absorption of light, etc.) more or less affects the luminescence performance and affects the quantum efficiency of luminescent powder particles. It is also found that although the initial brightness of the coated samples decreases to a certain extent, the attenuation trend and velocity are very similar to that of the uncoated samples. According to the data of the long afterglow luminescence performance test (emission peak area and afterglow time), the fluorescence intensity of the coated samples was calculated to be 97% of that before the coating, and the afterglow life was 98%. This further indicates that the presence of the coating layer has some influence on the luminescence performance. Properties of water-based luminescent paint: the coating modified luminescent powder and the uncoated modified luminescent powder were used as luminescent pigments respectively. Latex paint was prepared according to the same proportion and process conditions, and some of its main comprehensive properties were tested. They differ greatly in storage performance and water resistance. The coating with luminescent powder coated with silicon dioxide as pigment has good storage stability. After being placed in 3d, the coating starts to layer. After being placed for 1 month, there is no agglomeration. These results show that the aluminate long afterglow luminescent powder can be used in water-borne coatings after modification of silica surface, and the coating has better storage stability and water resistance. Using ethylene glycol as dispersion medium and sodium silicate silica as cladding agent, modification of luminescent powder particles by silica cladding can significantly improve the water resistance of luminescent powder particles, and at the same time has little effect on the long afterglow luminescence characteristics of luminescent powder. The coating modified luminescent powder is used as luminescent pigment for the water-based emulsion paint with good storage stability and water resistance.
Performance test of water-based luminescent powder: the water resistance of luminescent powder was measured by phs-10b digital acidity meter. During the measurement, the water resistance was qualitatively characterized by monitoring the change rate of pH value of aqueous solution containing luminescent powder. The spectral properties and afterglow attenuation of luminescent powders before and after coating were tested by hitachif-2500 fluorescence photometer.
Change of water resistance before and after modification of aqueous luminescent powder: the coating process of silica with Na2SiO3 solution as the coating material is actually the deposition process of hydrated silica (SiO2·xH2O) on the surface of luminescent powder. In the experiment, glycol was used as the dispersing medium to overcome the hydrolysis problem of luminescent powder. When dropping sulfuric acid solution,Na2SiO3 will have the same chemical reaction when encountering acid, and generate hydrated silica with different degree of polymerization. Silicic acid or hydrated silica with low degree of polymerization has very small particle size and high reactivity. It will firstly be adsorbed on the surface of luminescent powder through hydroxyl group and form nucleation points on the surface of luminescent powder, and then rapidly polycondensation to form a polymer of silicon. With the continuous progress of polymerization, the coating layer of dense silica begins to grow and finally forms a continuous solid silicon dioxide film on the surface of luminescent powder particles. After coating, the pH value of the aqueous solution hardly changed with time, and the water resistance was greatly improved. The results show that the silicon dioxide coating layer deposited on the surface of luminescent powder particles can protect the luminescent powder particles well and prevent the water from contacting with the luminescent particles.