Preparation And Optical Properties Of Ag-Enhanced NaYF₄:Yb³⁺,Tm³⁺Inverse Opal Photonic Crystals

The unique periodic structure of photonic crystals and the special photonic bandgap structure make it a hot spot of attention in recent years.When the spontaneous emission frequency of the fluorescent substance is located in the band gap of the photonic crystal,the spontaneous emission of the substance will have an inhibitory effect and thus be effectively regulated.This discovery has made it more widely used in display,sensing,thin film,biofluorescence labeling and so on.Fluoride has high up-conversion luminescence efficiency due to the characteristics of forbidden bandwidth,short absorption side wave,low phonon energy,and long infrared absorption side wave.As an excellent fluorescent material carrier,under the excitation of 980 nm infrared laser,silver elemental nanoparticles and NaYF₄:Yb³⁺,Tm³⁺nanoparticles are combined to realize the up-conversion luminescence of rare earth ions of various colors,and the selection has lower phonons.The energy NaYF₄ can be used as a doping matrix of Ag elemental nanoparticles and Yb³⁺,Tm³⁺,combined with the effect of plasmon resonance on the surface of noble metal element,so that more efficient upconversion luminescence efficiency can be obtained.In this paper,the rare earth ions were added to the NaYF₄ precursor prepared by the two methods,and then the silver element reduced by hydrothermal method was added to prepare NaYF₄:Yb³⁺,Tm³⁺precursor powder with silver elemental adhesion.The precursor solution was filled into polymethyl methacrylate?PMMA?microglobulin stone photonic crystal template,and the inverse opal structure was sintered by high temperature.The influence of several representative photonic band gap positions on upconversion luminescence was analyzed and discussed.The main contents of this paper are as follows:?1?Comparison of monodisperse polystyrene?PS?microspheres and monodisperse polymethyl methacrylate?PMMA?microspheres by soap-free emulsion polymerization.Polymethyl methacrylate opal crystals with band gaps at490 nm,556 nm and 656 nm were prepared by vertical deposition self-assembly method using slides as substrates.NaYF₄:Yb³⁺,Tm³⁺precursor powders with different lattice structures were prepared by solvothermal and hydrothermal methods,respectively.After adding Ag ions,the Ag ions were reduced to Ag element by methanol hydrothermal method,and Ag elemental nanoparticles were combined with NaYF₄:Yb³⁺,Tm³⁺powder.After dispersing and dissolving,it is filled into the opal photonic crystal template,and the corresponding temperature is selected for high temperature calcination to obtain the corresponding Ag@NaYF₄:Yb³⁺,Tm³⁺Inverse opal photonic crystal.?2?Measuring the transmission spectrum of the sample,XRD,XPS,SEM,up-conversion luminescence excited by 980 nm infrared light,and the like.The measurement results showed that the crystallization of the sample was good,and the microscopic morphology was granular and hexagonal.Under the same material composition,the luminescence of the sample with the inverse opal structure was3.36 times stronger than that of the opal structure.This result confirms that the inverse opal photonic crystal structure can effectively enhance the luminous efficiency of the luminescent material.Under the same structure,the luminescence intensity of the sample with Ag elemental nanoparticles increased by 6.71 times compared with the sample without Ag element.This result proves that when the electromagnetic surface wave of the plasmon resonance formed by the free electrons around the noble metal particles is superimposed and coupled with the excitation light field,the probability of electronic transition can be increased.The inverse opal photonic crystal structure samples of three different band gap positions were compared with the disordered?REF?samples,respectively,and the corresponding photon band gaps were obtained to give the respective luminescence peaks a significant modulation result.?3?The reason for the above results is studied from the perspective of energy level transition,and this enhancement is interpreted as the interaction of ground state absorption,energy excited state absorption,multiphoton process and energy cross relaxation.The surface plasmon resonance effect caused by the noble metal Ag element enhances the photon radiation intensity.When combined with the opal photonic crystal photonic band gap,the up-conversion emission energy in the blue,cyan,green and orange bands is simultaneously modulated by the photonic band gap:When the green emission light is at the center of the band gap,the blue emission is at the edge of the band gap,and the green emission is suppressed while the blue emission is enhanced.By analogy,the luminescence is enhanced when the luminescence peak position is at the photonic band gap edge,and vice versa.When all the emission peak positions are simultaneously at the photonic band gap edge,all the up-conversion luminescence simultaneously appears as luminescence enhancement.The experimental results verify the effects of the band gap center position and the band gap edge position and the photon state density weakening and enhancement on the spontaneous radiation transition.