The Preparation,optical Properties And Applications Of Nanocrystals/Quantum Dots Doped Polymer Optical Fibers

Trivalent rare earth ion doped inorganic nanocrystals and metal halide perovskite quantum dots have attracting lots of attention in scientific research due to their excellent optical properties,controllable and stable synthesis and diversified structure design.Both of them have great application potential in high-power laser,optical communication,lighting and display,energy saving and environmental protection,high-precision sensor and so on.However,inorganic nanocrystals and perovskite quantum dots which in the form of fluorescent powder or colloidal solution are difficult to be compatible with solid-state optical devices,limiting their further development and application on the advanced optical platform greatly.In recent years,embedding nanocrystals and perovskite quantum dots into transparent inorganic or polymer matrix to prepare solid-state optical devices has been attracting wide attention.It can not only enlarge the application scope of nanocrystals and perovskite quantum dots,but also improve the stability of perovskite quantum dots to develop advanced optical functional materials and applications.Compared with block or two-dimensional materials,one-dimensional optical fiber,as an indispensable photon platform,has the unique advantages of high-efficiency transmission rate,small volume,high integration.Fibers was uses in a wide range of applications such as high-precision optical sensors,lasers,lighting and so on.Therefore,it is an attractive research direction to integrate nanocrystals or perovskite quantum dots with optical fiber platform to apply their excellent optical properties.In this paper,the preparation techniques of LiYF₄ nanocrystals and CsPbBr₃ quantum dots compositing PMMA polymer fiber are developed based on the characteristics of doping materials and matrix material.As a result,LiYF₄@PMMA polymer optical fiber and CsPbBr₃@PMMA polymer optical fiber are successfully fabricated.More importantly,these preparation strategies are not limited to LiYF₄ nanocrystals and CsPbBr₃ quantum dots as the fluorescence center,nor PMMA as optical fiber matrix,but have broad applicability.As a result,it paves the way for the research of other optical functional materials composite polymer optical fiber.At the same time,we also have a detailed study on the optical properties and application prospects of these composite fibers,which will play a guiding role in the application and development of new composite fibers.Main achievements of this paper are as following:?1?LiYF₄ nanocrystals with a diameter of about 150 nm are prepared by the hydrothermal method.The LiYF₄@PMMA block with uniform luminescence and good transmittance was successfully fabricated by the“solution method”.A blue shift in the emission spectra of LiYF₄ nanocrystals was observed after the incorporation of nanocrystals in PMMA,which was mainly due to the change of rare earth ions'environment.Then we used lathe to process the LiYF₄@PMMA block into a cylinder and insert it into a commercial PMMA tube to obtain the optical fiber preform.Subsequently LiYF₄@PMMA polymer optical fiber was fabricated though“rod-in-tube method”.The resulted waveguide structure is complete without severe interfacial diffusion.Through the temperature sensing experiment,it is found that the luminescence of nanocrystals decreases with the temperature increasing,and the mechanism is explained.Therefore,the LiYF₄@PMMA polymer optical fiber is expected to be used in the field of optical functional composites such as optical sensing.?2?CsPbBr₃ quantum dots with a diameter of about 10 nm were prepared by the"hot injection method".They were then incorporated into the PMMA by"hot polymerization method".The emission spectra and lifetime curves of CsPbBr₃@PMMA block were analyzed.The emission spectra exhibit a blue shift and the fluorescence lifetime became longer after CsPbBr₃ incorporating into PMMA.To test fluorescence stability of CsPbBr₃@PMMA block in aqueous solutions and UV light,4 samples were soaked in acidic,neutral and alkaline aqueous solutions as well as exposed in 365 nm UV light respectively.All the samples show no significant luminescence degradation or detrimental chromatic shift after a certain time,indicating that the network structure of PMMA was very compact to ensure the luminescent efficiency of CsPbBr₃ quantum dots.In addition,we studied the influence of different temperature on the emission spectrum of CsPbBr₃@PMMA block.With the increase of the temperature from 30^oC to 80^oC,the luminescent intensity decreases smoothly and substantially.Besides,the FWHM becomes wider with the temperature increasing while the peak positions show independence of temperature.We also studied the influence of different pressure on the emission spectrum of CsPbBr₃@PMMA block.With the increase of pressure from 0 MPa to 50 MPa,the luminescent intensity of the sample decreased gradually.The mechanism of the above changes is explained.?3?The preparation techniques of CsPbBr₃@PMMA polymer optical fiber were explored and finally CsPbBr₃@PMMA polymer optical fiber was prepared by“capillary tube method”.Compare to the conventional“rod-in-tube”fiber-drawing method,this new technology can fabricate polymer optical fibers at temperature as low as 80^oC.As a result,the excellent optical properties of CsPbBr₃ quantum dots can be maintained during the fiber-drawing process instead of quenching at high temperature.Compared to the quantum dots doped glass fiber preparation method based on“in-situ crystallization”,in this method the colloid quantum dots were prepared by chemical synthesis so that it is easy to modify quantum dots through ions doping to meet different needs.The as-prepared CsPbBr₃@PMMA POF using"capillary tube method"possesses a smooth surface,clear core/cladding interface,complete waveguide structure and bright luminescence.This new fabrication strategy based on capillary tube highlights a general pathway to fabricate high-quality perovskite embedded polymer composite fiber with a complete core-cladding waveguide structure.Last but not least,we explored the application of CsPbBr₃@PMMA POF in the fields of optical fiber sensing,demonstrating its wide application prospects in optical fiber temperature sensing and pressure determination.