Investigation Of The Luminescence Emissions Of The Rare Earth Ions Controlled By The Photonic Crystals And The Surface Plasmons

Rare earth doped luminescent materials are developing rapidly,and they are widely used in phosphors,displays,X-ray imaging,lasers and optical fiber communication amplifiers.Later studies have found that when Yb³⁺ions are co-doped with rare earth ions(Er³⁺,Tm³⁺,etc.),rare earth ions can emit high-frequency light excited by low-frequency light,which is,the frequency upconversion effect.This effect provides the possibility for the utilization of low-energy long-wave light.However,due to the many emission energy levels of rare earth elements,other emission light besides available wavelength will be generated when excited.How to regulate these emission light is the focus of the current research.Photonic crystals have photonic band gap structure and special photon localization,which can prevent the propagation of photons falling into the band gap.It plays an important role in manipulating the luminescence of the rare earth elements.In particular,the regulation of the spontaneous emission of electric and magnetic dipoles of rare earth ions will be the focus of this paper.In addition,the surface plasmon effect of gold nanostructures not only enhances the upconversion luminescence,but also has a strong quenching effect under some conditions.Its optical property is that it can maintain the electron oscillation called surface plasmon,thus producing an electromagnetic field confined to the metal surface.therefore,the effect of surface plasmon on upconversion luminescence is worthy of further study.Starting with the preparation of inverse opal photonic crystals and gold nanoparticles,this paper explores the regulation of rare earth element luminescence and upconversion luminescence.The main contents of this paper are as follows:（1）The YVO₄:Tm³⁺,Yb³⁺,Er³⁺inverse opal samples of different sizes were prepared by the classical precipitation method.The corresponding frequency upconversion photoluminescence spectra were obtained under the excitation of 975nm laser.In the inverse opal samples,photonic crystals have a strong modulation effect on the radiation peak intensity of rare earth ions in the visible band,and the radiation peak intensity varies with the size of polystyrene（PS）microspheres.The inverse opal photonic crystal samples with PS microspheres size of 250 nm show better frequency upconversion white light characteristics when the Er³⁺ion concentration is 3%.The blue part of the white light is mainly composed of the radiant light of the rare earth Tm³⁺ion（476 nm,¹G₄→³H₆）and the frequency doubled（SHG）signal of the incident light,and is mainly composed of the SHG signal.The green light part are composed of the rare earth Er³⁺ion radiant light(525nm,²H_11/2→⁴I_15/2;550,⁴S_3/2→⁴I_15/2).The red light part are composed of rare earth Tm3+（648 nm,¹G₄→³ F₄）and Er3+ion（659 nm,4F9/2→4I15/2）.（2）YVO₄:Er³⁺inverse opal samples of different sizes were prepared,and excited by lasers with wavelengths of 450 nm and 975 nm,respectively.The corresponding fluorescence spectra of visible light and near infrared light were obtained.By comparing the emission peak intensity of Er³⁺ions in green band（525nm,550 nm）and near infrared band（1533 nm,1155 nm）,it is found that the size of photonic crystals has a great influence on the luminescence of rare earth Er³⁺ions.Especially in the near-infrared band,the fluorescence of 1533 nm is significantly reduced in the inverse opal photonic crystals with the PS microspheres size of 400 and500 nm,while the fluorescence at 1155 nm is significantly enhanced.For the inverse opal photonic crystals of 400 nm,the fluorescence intensity at 1155 nm exceeds the fluorescence intensity at 1533 nm.The above characteristics confirm that the inverse opal photonic crystal has a strong regulatory effect on the fluorescence of YVO₄:Er³⁺in the visible and near-infrared bands.（3）The fluorescence spectra of LaPO₄:Eu³⁺nanocrystals and the LaPO4:Eu³⁺inverse opal photonic crystals with the PS microspheres size of 400 nm is compared under excitation of a 325 nm laser.Through the analysis,it is found that the inverse opal photonic crystal plays an important role in regulating the magnetic dipole radiation of Eu³⁺ions.The relative radiation intensity of the magnetic dipole radiation⁵D₀→⁷F₁and the electric dipole radiation ⁵D₀→⁷F₂increased by 1.4 times,which is much higher than that obtained by Au periodic nanostructures abroad.At the same time,by exploring the effects of different sizes of photonic crystals on magnetic dipole and electric dipole transition,it is found that inverse opal samples have different degrees of enhancement effect on magnetic dipole radiation.Another important characteristic is that the intensity of⁵D₀→⁷F₄fluorescence radiation at 695nm is obviously enhanced and becomes the main fluorescence radiation peak,which is caused by the energy band structure of photonic crystals.（4）The effect of Au nanoparticles on the luminescence of YVO₄:Yb³⁺,Er³⁺(Ho³⁺)nanocrystals was investigated.When YVO₄:Yb³⁺,Er³⁺(Ho³⁺)nanocrystals are coupled with the Au nanocrystals,the upconversion fluorescence peaks of Er³⁺ions located at525 nm and 550 nm have obvious quenching effect,while in the mixed samples of YVO₄:Yb³⁺,Ho³⁺and Au nanocrystals,the intensity of the upconversion emission peak is almost unchanged.The quenching effect is related to the relative position of the fluorescence peak and the absorption peak of Au nanoparticles.If the two are close,the quenching effect is more obvious.In addition,the quenching effect is also related to the excitation intensity.The above effect confirms that the quenching effect is related to the energy transfer between nanocrystals and Au nanoparticle plasmons.