Study On Optical Properties And And LED Application For Inorganic Perovskite Nanocrystalline Composite Structure

As a new type of quantum dot material,all inorganic lead halide perovskite CsPbX₃（X=Cl,Br,I）quantum dots（PQDs）have a series of excellent optical properties,such as wide absorption cross section,narrow emission line,high luminescence quantum efficiency,arbitrary adjustment of luminescence peak position in the visible light range,relatively stable structure and easy preparation.It has broad application prospects in the field of lighting and display,so it is favored by scientific researchers and has gradually become the forefront and hotspot of academic research in the field of optoelectronic materials and devices.However,the stability of lead halide perovskite PQDs in water,oxygen and heat is not good,especially the red-light materials represented by CsPbI₃ PQDs are extremely unstable,which seriously limits their practical application and becomes a key problem to be solved.Mesoporous SiO₂,CaF₂ nanospheres and organic metal framework（MOF）can encapsulate perovskite PQDs,so as to improve the stability of perovskite PQDs.In addition,rare earth ions have narrow emission lines,high color purity and rich transition energy levels.If the composite structure of perovskite PQDs is constructed and the way of energy transfer is used,the problem of red-light instability of perovskite PQDs can be solved.In view of this,this paper focuses on how to realize the encapsulation and energy transfer of perovskite PQDs with rare earth doped CaF₂ and MOF mesoporous structures.Among them,including how the encapsulation of these mesoporous structures improves the stability of perovskite PQDs,whether the energy transfer between rare earth ions in mesoporous structures and perovskite PQDs is radiation energy transfer or non-radiation energy transfer,and which energy transfer mode is dominant.The details are as follows:（1）CsPbBr_xI_3-x（0≤x≤3）perovskite PQDs were filled into mesoporous CaF₂ nanospheres（～600 nm）doped with rare earth aion Ce³⁺and Tb³⁺,and formed CaF₂:Ce,Tb&CsPbBr_xI_3-x composite structure.This structure not only improves the stability of a series of red CsPbBr_xI_3-x perovskite PQDs,but also greatly maintains the luminous efficiency of red perovskite PQDs.This is because CaF₂ acts as a shell to protect perovskite PQDs,and the energy transfer of rare earth ion Tb³⁺sensitizes the red-light emission of perovskite PQDs.Under 300 nm excitation,the maximum photoluminescence quantum yields（PLQYs）of CaF₂:Ce,Tb&CsPbBr_1.2I_1.8 composite structure is 65.6%.After being placed in the air for two months,the red PLQY of the composite can maintain 71%of the initial value,which shows that this composite structure effectively improves the stability of perovskite PQDs.Finally,the composite was mixed with PMMA and coated on 365 nm In Ga N chip to produce red LEDs.The white LEDs prepared by the combination of CaF₂:Ce,Tb&CsPbBr₃、CaF₂:Ce,Tb&CsPbBr_1.2I_1.8 composite and 450 nm chip also showed good performance,and its best luminous efficiency was 61.2 LM/W.（2）CsPbCl_xBr_3-x:Mn（0≤x≤3）perovskite PQDs were filled into the MOF structure doped with rare earth elements Ce and Eu（～80.0μm）MOF:Ce,Eu&CsPbCl_1.5Br_1.5:Mn composite structure.The structure can not only enhance the environmental stability of perovskite PQDs,but also sensitize the red-light emission of Eu³⁺ions through the radiation energy transfer between perovskite PQDs and Eu³⁺ions.Firstly,Mn Cl₂ is doped into CsPbBr₃ perovskite PQDs to form Mn²⁺ion doped CsPbCl_xBr_3-x（0≤x≤3）blue PQDs,which greatly improves the blue luminescence efficiency of CsPbCl_xBr_3-x PQDs and realizes the series regulation of its emission wavelength（450-517 nm）.The results show that PQD_S with an emission wavelength of about465 nm can well sensitize the red-light emission of MOF doped Eu³⁺ions.This is because 465 nm is the intrinsic excitation wavelength of Eu³⁺ions,which realizes good radiation energy transfer.In addition,due to the co doping of Ce³⁺and Eu³⁺ions in MOF structure,the effective non-radiative energy transfer of Ce ions to Eu ions can be realized.Finally,high efficiency red-light emission with fluorescence quantum yield of 54.6%in MOF was obtained.That is,we synthesized MOF:Ce,Eu&CsPbCl_1.5Br_1.5:Mn composite structure emits stable and efficient red light,which indirectly solves the problem of instability of perovskite PQDs red light material.Finally,the composite MOF:Ce,Eu&CsPbCl_1.5Br_1.5:Mn and PMMA were mixed and coated on the commercial chip of 285 nm LED to produce efficient red LEDs.The red LEDs show great potential as a supplementary light source for plant lighting.