Emission Color-tunable Mechanism And Application Of The Thermo-UV-responsive Luminous Fibers

Luminous fibers generally refer to a class of functional fibers made of rare earth luminescent materials and polymers.In recent years,with the development of rare earth long-afterglow materials,researchers have successfully prepared luminous fibers of various luminous colors.These fibers have a variety of colors and excellent afterglow performance.However,the luminous color is difficult to control,and the ability to respond to temperature and ultraviolet（UV）is weak,which limits the application of luminescent fibers in smart textiles.Therefore,to solve the above problems,this study introduced the crystal violet lactone thermochromic material and spiropyran photochromic material into the luminescent fiber.Furthermore,based on the additive color theory,the thermo-UV-responsive luminescent composite fibers with controllable full-color emissions were successfully prepared.The mechanism of the synergistic chromic effect of temperature and UV were investigated.Besides,the light transfer mechanism of rare earth luminescent materials in thermo-UV-responsive fibers was also studied in detail.The main contents are as follows:（1）The three primary color rare earth long-afterglow materials were prepared by high temperature solid-state reaction method.They are red luminescent material Y₂O₂S:Eu³⁺,Mg²⁺,Ti⁴⁺,green luminescent material Sr Al₂O₄:Eu²⁺,Dy³⁺and blue luminescent material Sr₂Mg Si₂O₇:Eu²⁺,Dy³⁺,respectively.Through the XPS,excitation and emission spectrum,afterglow analysis and luminous quantum efficiency test methods,the photoluminescence mechanism and the source and type of trap in the matrix were analyzed in detail.Furthermore,the internal long-afterglow luminescence mechanism was explained by a theoretical physical model.Based on the three kinds of long-afterglow materials,the three-dimensional code was successfully prepared,which laid a certain foundation for the subsequent work.（2）To investigate the light transfer mechanism of single rare earth long afterglow material in photochromic fiber,three primary luminescent materials and three kinds of spiropyran photochromic pigments were mixed into the fiber matrix respectively by the wet spinning process.By analyzing the reflectance spectra and emission spectra of the as-prepared fibers before and after UV excitation,the luminescence and photochromic properties of the as-prepared fibers were discussed in detail.（3）In view of the light transfer mechanism of double-doped luminescent materials in the photochromic fibers,the Sr Al₂O₄:Eu²⁺,Dy³⁺and Sr₂Mg Si₂O₇:Eu²⁺,Dy³⁺were used as the luminous source of the fiber,and spiropyran photochromic dye（white-purple）was used as the photochromic source of the fiber.The photochromic double-doped luminescent fiber was prepared by the wet spinning process.The results indicate that the luminescence of the two long-afterglow materials is independent in the fiber,and the addition of spiropyran dye does not directly change the luminescence center of the long-afterglow materials.After UV excitation,the spiropyran form transfers to the merocyanine form,which can partially absorb the emitted light of the long-afterglow materials in this region,thereby indirectly affecting the light transmission of the long-afterglow materials.（4）By analyzing the excitation spectra of the three long-afterglow luminescent materials prepared in the previous chapter,we found that the excitation ranges of the three materials all covered the ultraviolet region.In this study,365 nm was selected as the excitation light source,and the prepared three primary color luminescent materials were combined in different ratios.By comparing the changes of emission spectrum of different combinations,it is found that the luminous color of the mixed long afterglow material is linearly related to the proportion.Besides,the white luminous material is successfully prepared.（5）To prepare the thermo-UV-responsive composite fibers with tunable full-color emission ability,different ratios of the crystal violet lactone thermochromic pigments,spiropyran photochromic pigments and three primary luminescent materials were incorporated into the fibers via the wet spinning process.By analyzing the reflectance spectra and emission spectra of the prepared fibers under different stimulus conditions,the mechanism of synergistic chromic effect response to temperature and UV were investigated.Besides,the light transfer mechanism of mixed rare earth luminescent materials in fibers was also studied in detail.The results showed that spiropyran photochromic pigments and crystal violet lactone thermochromic pigments exhibited different absorption capacities to visible light bands under different structures,and could selectively absorb the emitted light of luminescent materials in the fibers,thus affecting the light transmission and indirectly changing the light color,similar to the effect of light conversion agents.According to the results,a series of thermo-UV-responsive luminescent fibers were prepared by adjusting the proportion of each component,and finally the thermo-UV-responsive white fiber was successfully prepared.The mechanical properties,chromic properties,emission spectrum and fatigue resistance of as-prepared fibers were thoroughly investigated.Based on the unique properties,the fibers are taken as real-time,energy-free visual wearable sensors to monitor the temperature and UV.In addition,the obtained fibers are further explored as tags for information encryption.Overall,this work demonstrates the great potential of the as-prepared fibers for smart textiles.