Construction,interface And Properties Of Eu³⁺ Doped Nano-composite Luminescent Materials

The Eu³⁺doped nanocomposite luminescent material not only has potential application prospects in NUV excitation LED optoelectronic devices and optical functional compounding,but also is an ideal research object to use fluorescence signal to reveal the interface and liquid medium environment of related nanocomposites in the field of basic research.However,the single-host luminescent materials doped with Eu³⁺is more serious the temperature quenching with longer the absorption wavelength.The energy transfer between different rare earth ions in single host is easy to lead to luminescence quenching.In order to solve these problems,we constructed composite materials with different optical activity.Using the Eu³⁺fluorescence signal to explore basic scientific issues such as the interface state of composite materials,interface resonance energy transfer,functional recombination,and the influence of different media environments on these states and properties.In this paper,based on the excellent red light emission performance and electric dipole/magnetic dipole transition characteristics of Eu³⁺ions,we choose the larger Eu³⁺doped porous oxides and two-dimensional oxide nanosheets to compound with perovskite halides or rare earth complexes with excellent optical properties,and carrying out related research.The main research results obtained in this dissertation are as follows:（1）We have investigated the luminescent properties of halide perovskites embedded in porous oxides structure.Firstly,we synthesize the inorganic porous material Ca_0.9Eu_0.1Mo O₄by the hard template method,referred to as CEMO,and Cs Pb Cl_1.5Br_1.5（CPCB）has been synthesized in situ in the porous oxide to prepare the CPCB@CEMO composite material.The composite material has exhibited had luminescence discoloration phenomenon with the ultraviolet irradiation time changing.XPS and fluorescence spectroscopic analysis demonstrate that the Eu³⁺/Pb⁰-Eu²⁺/Pb²⁺redox reaction occurs at the interface of the composite material,resulting in the enrichment of Cl^-ions at the interface of the composite material and changing the local crystal environment of Eu³⁺on the oxide surface;Br^-ions preferential concentrates within the halide perovskite layer.Light decay cycling experiments demonstrate that the interface redox process under UV light irradiation is beneficial to enhance the stability of halide perovskites.Since the perovskite material is composed of grains and amorphous phases,the contact between the halide grains and the oxide is poor at the interface,and the energy transfer between the halide and Eu³⁺cannot be achieved.（2）Based on the research of porous oxides,then we has introduced rare earth complex Tb（phen）₂（NO₃）₃（abbreviated as Tb-phen,where phen refers to phenanthroline）in porous CEMO oxides,and explore luminescence quality of Tb-phen@CEMO composite.Firstly,the Tb-phen@CEMO composite is successfully constructed by in-situ crystallization.The excitation/emission spectrum and the fluorescence decay curve of Tb³⁺/Eu³⁺all indicate the existence of F?rster resonance energy transfer from rare earth complexes to Eu³⁺in the composite material;La-phen@CEMO composite material is used to eliminate out the possibility of phen?Eu³⁺energy transfer,and confirming that The energy transfer process of Tb-phen@CEMO composites is phen?Tb³⁺?Eu³⁺.As expected,the composite material can effectively avoid the luminescence quenching effect that easily occurs when Tb³⁺and Eu³⁺are in the same lattice,and its luminescence thermal stability is also improved.（3）The photoresponse and surface/interface properties of Eu³⁺-doped perovskite layered oxide nanosheets to different medium environments are investigated.Ultrathin TBA-Ca_1.8Eu_0.1Na_0.1Nb₃O₁₀nanosheets（TBA+-NSs）has been prepared by soft chemical liquid phase exfoliation,whose surface is modified by tetrabutylammonium hydroxide（TBA）molecules.The effective refractive index n_effand the red-orange ratio R/O value of the surrounding medium of Eu³⁺can be calculated by the decay rate change of the magnetic dipole transition radiation of Eu³⁺with different solvent media;it is found that the stronger interface force between long alkyl chains solvent molecules and TBA⁺ligands can weaken the interaction between the ligand and the nanosheet,which makes the nanosheet curl more seriously in the macroscopic view.Compared with the smaller ligands,the larger TBA⁺ions can hinder the re-stacking of TBA⁺-NSs.For ultrathin nanosheets,both the larger number of atomic layers and the smaller size of ligands can suppress the change of the two-dimensional structural characteristics of the nanosheets in the medium.（4）On the basis of perovskite oxide nanosheets,we also deeply investigated the interfacial resonance energy transfer between rare earth complexes and oxide nanosheets.First,the Tb-phen is introduced by in-situ crystallization on the surface of oxide nanosheets TBA-Ca_1.8Eu_0.1Na_0.1Nb₃O₁₀（abbreviated as NSs）,and Tb-phen-NSs composites are prepared.The rare earth complexes can be uniformly distributed on the nanosheets surface through the analysis of its crystal structure.The resonance energy transfer process at the interface has been demonstrated by the variation of excitation spectrum,emission spectrum and lifetime decay.The lifetime decay curve also illustrates the efficient resonance energy transfer of phen?Tb³⁺?Eu³⁺.In addition,Tb³⁺and Eu³⁺ions radiation decay rate variation in the medium environment determined that the efficiency of energy transfer increases gradually with the increase of solvent molecular chain length.