Surface Water-repellent Modification Of SrAl₂O₄:Eu²⁺,Dy³⁺ And Its Application To Luminescent Fibers

Rare earth strontium aluminate[SrAl₂O₄:Eu²⁺,Dy³⁺(SAO)]is a rare earth long afterglow luminescent material with excellent luminescence performance,which has the advantages of high quantum efficiency,excitation bandwidth,long afterglow time,more stable chemical properties and non-radioactive,etc.It is widely used in coatings,textiles,glass and plastics.However,the water resistance of SAO powder is poor,and hydrolysis is easy to occur when exposed to humid air or in contact with water for a long time.The hydrolysis of SAO powder will produce a large amount of OH-,which will increase the p H of the system,affecting the acid-base balance of the system and destroying the crystal structure of the material,seriously affecting the afterglow brightness of its luminescence performance,and it is easy to agglomerate in the organic system,limiting the secondary processing of SAO powder and its application in complex environments.This limits the secondary processing and application of SAO powders in complex environments.Inorganic coating can improve the water resistance of SAO powder,but the organic compatibility is poor;organic coating can improve the compatibility of the powder,but it is unstable in aqueous solution.To address the above problems,this paper aims to introduce a composite inorganic/organic coating layer on the surface of the powder,thus enhancing its stability in aqueous solution and organic compatibility in polymer matrix,and broadening the application of the powder in luminescent fibers and coated fabrics.The main studies and conclusions are as follows.Firstly,inorganic coating(SiO₂,Al₂O₃,CaF₂ and MgF₂)was applied to the surface of SAO powder by sol-gel and liquid phase deposition.The experimental results show that the spectral waveforms of the powders before and after coating remain the same,and the coating process and inorganic coating layer do not damage the crystal structure of the powders;the inorganic coating layer plays a protective role for the powders.Secondly,in order to improve the dispersion of SAO powder in polymer matrix,three coupling agents,Si69,KH570 and SA,were used to organically modify its surface,and the surface modification effect was investigated using contact angle tester and other instruments.The results showed that:the coupling agents were successfully adsorbed on the surface of SAO powder by hydrogen bonding and van der Waals forces;the surface properties of the modified powder changed from hydrophilic to hydrophobic and the surface free energy decreased;the organic coating layer improved the compatibility of the powder with organic matter.Combining the advantages of strong water resistance of inorganic coating and good dispersion of organic coating,the inorganic/organic composite coating of SAO powder was carried out,and the microscopic morphology,water resistance and afterglow characteristics of the powder before and after coating were characterized by using fluorescence spectrometer and other instruments.The results showed that the composite coating repaired the cracks on the original powder,reduced the influence of external environment on the powder,and thus improved the stability of the powder.The composite cladding layer did not change the decay law of SAO powder,and its influence on the afterglow brightness was small.Finally,long afterglow luminescent fibers were prepared by wet spinning with polyacrylonitrile(PAN)as the fiber substrate and compound-coated SAO powder as the additive,and the effects of different powder contents on the fiber properties were analyzed.The tests revealed that the powder was uniformly dispersed in the fiber;the luminescent intensity of the fiber increased with the increase of the powder content;the fiber could maintain its original luminescent intensity after being immersed in water for a period of time.In addition,the polyester fiber-based water-repellent luminescent coated fabric was designed by means of coating finishing,and the powder was compatible with water-based polyurethane(WPU)and the fabric emitted light in yellow-green color.