Study On Luminescent Properties And Application Of Doped Perovskite-based Long Afterglow Crystals

As a kind of commercial functional material,afterglow material is closely related to people’s daily life and gaining increasing research interest.However,the research focus of afterglow was mainly on powder samples,leaving few reports on crystal samples.Limited by the severe scattering issue from powder samples,many advanced techniques such as volumetric display and 3-dimensional encryption were impossible.Instead,the transparent afterglow crystals were proposed as an efficient afterglow candidate,and raised considerable attention recently.As a low-lattice-energy and wet-chemistry-accessible matrix,halide perovskite has many excellent optical properties,such as nearly 100%photoluminescence quantum yield（PL QY）and tunable band gap,which make it an appealing candidate in the field of optoelectronics.In this thesis,we designed and synthesized perovskite-based afterglow single crystal materials,which successfully achieved efficient red or green afterglow emission by doping Mn²⁺or Tb³⁺ions.In the first chapter,the research background and related synthesis methods of perovskite were introduced.Meanwhile,as a traditional luminescent material,the afterglow material also has irreplaceable advantages.At present,most of the relevant reports were about the afterglow powders,leaving few reports about the afterglow crystals;the application range of the afterglow materials were greatly limited by the severe diffraction from powder samples.Therefore,it was necessary to develop new afterglow materials of transparent crystal.Due to the synthesis of perovskite crystal was relatively simple,using a simple hydrothermal method,hot-injections,reverse microemulsion method could synthesize a few nanometers to a few centimeters range of crystal materials,and rare-earth ions/transition-metal ions as adjusting the afterglow luminescence color doped ions were also confirmed could effectively doped into perovskite lattice.Therefore,we considered exploring perovskite-based afterglow crystals with excellent luminescence properties by combining perovskite with rare-earth ions or transition-metal ions,so as to broaden the field of afterglow research.In the second chapter,transparent Cs₂Na Sc Cl₆ single crystal with a size of about 1 cm was grown by simple hydrothermal method,which exhibited weak blue broad-peak emission under UV light.In contrast to the pristine crystal,Cs₂Na Sc Cl₆crystal doped with Mn²⁺ions exhibited a dual-peak PL profile in blue and red region.By investigating the dynamics of the exciton recombination,the energy transfer between the self-trapping exciton and Mn²⁺ions in the crystal was revealed.Concurrently,we also found that the Cs₂Na Sc Cl₆:x Mn²⁺single crystal irradiated by X-ray showed an extended afterglow up to 1 hour in the red region after ceasing the excitation source.In addition,it was found that the crystal has remarkable photostimulation phenomenon.By changing the doping concentration,the duration and intensity of the afterglow were optimized,and the trap depth and afterglow mechanism of the red afterglow were analyzed and explained.The successful doping of Mn²⁺proved that the lead-free double perovskite Cs₂Na Sc Cl₆ was an excellent afterglow matrix material,which was expected to realize the tuning of afterglow color by doping process.In the third chapter,Tb³⁺ion was selected as the activator to overcome the caveats of Mn²⁺ion activated afterglow crystal,such as low PL QY and short afterglow time.The experimental results showed that the PL QY of Cs₂Na Sc_1-xCl₆:x Tb³⁺single crystal was elevated up to 98.2%,and the afterglow duration was up to 12 hours.The transient fluorescence attenuation curves of the materials were tested and it was found that this was caused by the cross relaxation between Tb³⁺ions.Concurrently,the materials could be readily excited by X-ray,and bright green afterglow was also observed when the X-ray was turned off.By optimizing the doping concentration and synthesis conditions,the intensity of afterglow was still one order of magnitude higher than that of the background within 12 hours after the X-ray light source was turned off,representing a breakthrough in afterglow duration.Then,the thermal cleaning experiment was carried out and the afterglow mechanism of the material was systematically studied by peak-type fitting method,and the afterglow mechanism was proposed.Based on the improved output of transparent crystals,a"Radiation-Storage Battery"was proposed as a proof-of-concept experiment,which may find its application in outer-space energy harvesting.Finally,the chapter 4 summarized the work done in this thesis in brief,combined with the research status of zero-dimensional perovskite and afterglow materials,and put forward some prospects for existing problems.