Study On The Afterglow Characteristics And Trap Level Distribution Of Luminescent Fiber

Based on rare earth elements doping host material to form the trap level and thecharateristics of electron energy level transition, the luminescent fiber having afterglow decaycharacteristics was made by using long-afterglow materials and fiber forming polymer.Luminescent fiber was prepared using SrAl₂O₄:Eu²⁺,Dy³⁺as luminescent raw materials andPET chips as polymer matrix by melt-spinning process. Firstly, the afterglow characteristicsand trap level distribution change of SrAl₂O₄:Eu²⁺,Dy³⁺and dispersing in fiber were studied,and the afterglow process dynamics model of luminescent fiber was set up. Then, on the basisof above research, the effect of spinning raw materials formula including the grain size andcontent of SrAl₂O₄:Eu²⁺,Dy³⁺, polymer base materials PP、PET、PA6, blue、green、yellow andred inorganic pigments and light excitation conditions on afterglow properties and trap leveldistribution of luminescent materials in fiber were mainly analysed, and influence mechanismwas illustrated as well. Next, by means of long time storage, insolation, washing, hightemperature and acid-base solvent treatment, the stabilities of afterglow properties wereobserved and analysed. Finally, by analysing the method of converting light color ofluminescent fiber, the effects of inorganic pigments, the substrate element of luminescentmaterial and activating agent on the light color of afterglow were studied, and the influencemechanism of them were clarified.The results showed that the SrAl₂O₄:Eu²⁺,Dy³⁺particles were dispersed randomly anduniformly, and there was no visible conglobation happening within the fiber. The complexmanufacturing process did not destroy the phase of SrAl₂O₄:Eu²⁺,Dy³⁺and physicochemicalproperties of polymer matrix, which ensured luminescent material in the fiber keeping a goodafterglow characteristics. The initial afterglow brightness of luminescent fiber was obviouslylower than that of SrAl₂O₄:Eu²⁺,Dy³⁺, but the time of each decay process of luminescent fiberwas more than that of SrAl₂O₄:Eu²⁺,Dy³⁺. Compared with the thermoluminescence peakSrAl₂O₄:Eu²⁺,Dy³⁺, that of luminescent fiber was slightly shift to the direction of hightemperature, which was in favour of forming a longer lifetime of afterglow, butthermoluminescent peak intensity of the fiber was low on the contrary. With the extension ofwaiting time after excitation, the trap level depth of luminescent fiber basically had no change.I=I0/（1+bt）2function was deduced to fit the afterglow decay curves of the fiber well, and thethermoluminescent and afterglow decay more accorded with second order kinetics law.The content and grain size of SrAl₂O₄:Eu²⁺,Dy³⁺in the fiber affected the afterglowcharacteristics of luminescent fiber, which concluded that the grain size of5-10μm andcontent of4-10wt%would meet with the requirements of spinnability and afterglowbrightness usage. The polymer base materials of PP, PET, PA6affected the initial afterglowbrightness and time, which was related to the energy loss degree in the process of lightexcitation and emission. The closer the contrast of hue of pigments and colored light of thefiber was, the higher the afterglow brightness of the fiber was. The selective absorption to thecolor light of pigments affected the amount and speed of carriers released by the trap level ofSrAl₂O₄:Eu²⁺,Dy³⁺in the fiber, which coincided with the results of the afterglow curves basically. The effect of light excitation conditions on afterglow properties of the fiber did notpresent linear change. The stronger the light excitation intensity was, the faster the speed ofafterglow attenuation time was. Increasing the excitation time did not prolong the afterglowlife effectively. The light exciation conditions did not change the trap level depth, butincreasing the electronic concentration of trap level, which showed the stronger the excitationintensity was and the longer the excitation time was, the higher the relative intensity ofthermoluminescence was.After storage of12months with constant temperature and humidity, exposure to light of5h, placing with high temperature of80℃, water soak of4h and acid-base solvent contactingof5min, the afterglow brightness and time of the fiber did not change distinctly andafterglow property did not affected yet. It was indicated that luminescent fiber had a goodafterglow stability of resistance to durability, light, high temperature, washing and chemistry,But excessive high temperature or long time of acid-base material erosion and water soak cancause the afterglow brightness of luminescent fiber decreasing to some degress.The red shift and blue shift of the emission spectra for chromatic luminescent fiberoccurred because of inorganic pigments selectively absorption to the yellow-green glow. Thatis to say, compared with the yellow-green light emitted by SrAl₂O₄:Eu²⁺,Dy³⁺, the afterglowlight color of chromatic luminescent fiber were changed and more tended to the hue ofpigments. By contrast of the emission spectra of SrAl₂O₄, Sr₂MgSi₂O₇, and （Sr,Ca）₂MgSi₂O₇based materials, it was discovered that changing the substrate element and proportion ofluminescent material in the fiber can convert and control the afterglow light color ofluminescent fiber, and that activated agent Eu，Dy，Nd doping and content had little effects toafterglow light color of luminescent materials, but changed its afterglow properties and traplevel distribution greatly. Using the combination principle of trichromatic color can get moreafterglow light color of luminescent fiber, therefore, it was the future main research ofpreparing luminescent fiber with blue color light.