Preparation And Optical Properties Of Ag-Assisted Yb³⁺, Er³⁺ Double-doped NaYF4 Inverse Opal

Rare earth ion doped up-conversion luminescent materials combine nanomaterial properties and optical properties,and have broad prospects in many aspects.If the regulation of luminescence process and the improvement of luminescence efficiency can be realized at the same time,it is the potential value further development for such materials.The periodic dielectric structure of the photonic crystal has a photonic band gap characteristic,which can control the flow of photons and control the luminescence process.The noble metal plasma can resonate with the incident light,and the superposition of the self-electromagnetic field and the excitation light field is superimposed,so that the possibility of radiation transition is increased and the luminous efficiency is enhanced.In this paper,the Ag-assisted inverse opal structure simultaneously achieves the regulation and efficiency enhancement of luminescence in the up-conversion process.In order to achieve the best effect of the upper transformation,this paper selects NaYF₄ with lower phonon energy and higher energy level matching Yb³⁺and Er³⁺for further research.The specific research contents are as follows:?1?The preparation of two kinds of polymer microspheres by soap-free emulsion polymerization,by comparing the experimental cycle,operation difficulty and mechanical strength of polystyrene?PS?and polymethyl methacrylate?PMMA?microsphere polymerization process,PMMA was selected for subsequent opal photonic crystal self-assembly and construction of inverse opal photonic crystal structure.The opal crystal photonic crystals were self-assembled by flow rate controllable vertical deposition self-assembly method and natural vertical sedimentation.Through the comparison of the experimental results,the natural vertical sedimentation method with more convenient operation,larger effective area of the sample and better optical performance of the sample was used for the subsequent self-assembly of the opal.Yb³⁺,Er³⁺double-doped NaYF₄ powders with different lattice structures were prepared by solvothermal method and hydrothermal method.Then Ag ions were reduced to Ag by methanol,and Ag-attached Yb³⁺,Er³⁺double-doped NaYF₄ precursors were prepared,and utilized The inclined surface is infiltrated into the PMMA opal photonic crystal,and the Ag-attached Yb³⁺,Er³⁺double-doped NaYF₄ inverse opal structure is constructed by high temperature calcination.The 980 nm laser was used to excite whether NaYF₄:Yb³⁺,Er³⁺samples?S1-3?with Ag-assisted and inverse opal structure were compared.The effects of elemental Ag and inverse opal structure on their luminescence were analyzed.And the luminescence spectra of the three sets of inverse opal samples?IOPC1-3?with the band gap positions at 487 nm,511 nm and 595 nm were compared with the disordered pore structure samples?REF?,and the regulation mechanism of photon band gap on upconversion luminescence was analyzed.Corresponding to²H_11/2?⁴I_15/2?524nm?,⁴S_3/2?⁴I_15/2?546nm?and ⁴F_9/2?⁴I_15/2?656nm?energy level transition processes,respectively.?2?The results show that the S3 sample with Ag element is 8.7 times luminescence than the S1 sample without Ag element,indicating that the electromagnetic field generated by the noble metal plasmon resonance is superimposed with the excitation light field,which can increase the photon transition probability.The S3 sample with inverse opal structure was 2.3 times luminescence than the S2 sample without this structure,indicating that the microscopic pore structure and thin-walled framework of the inverse opal contribute to the enhancement of luminous efficiency.By comparing IOPC with REF,it is found that when the spontaneous radiation falls in the photonic band gap range,its up-conversion luminescence is suppressed.When the spontaneous radiation is located at the band gap edge,its up-conversion luminescence is enhanced,and the 656 nm red light is enhanced.It is due to the cross-relaxation?CR?process of Er³⁺:²H_11/2+⁴I_15/2?⁴F_9/2+⁴I_13/23/2 and the energy reverse transfer?EBT?process between Er³⁺and Yb³⁺ions:²H_11/2/⁴S_3/2(Er³⁺)+²F_7/2(Yb³⁺)?⁴I_13/2(Er³⁺)+²F_5/2(Yb³⁺).