Research On LiBaF₃:Yb³⁺,Er³⁺ Optical Bistability And KYb(MoO₄)₂:Er³⁺/Tm³⁺/Ho³⁺ Photoluminescence Properties

Rare earth doped luminescent materials have very unique optical properties that can be widely used in biological imaging,optical storage,all-optical logic gates,display and other fields.The design and preparation of new rare earth doped phosphors,studying the PL mechanism,improving luminescence efficiency,and expanding new application fields have important scientific significance and great application potential.In this thesis,two series of nanophosphors,namely Yb³⁺-Er³⁺codoped LiBaF3 and Er³⁺,Ho³⁺,Tm³⁺single-doped KYb(MoO₄)₂,are designed and prepared.The optical bistability properties and PL mechanism have been studied,respectively.The main contents are as follows:Firstly,the technological process and parameters of Li_nBa_mF₃:0.2Yb³⁺,0.01Er³⁺and Li_0.4Ba_0.6-x-yF₃:x Yb³⁺,yEr³⁺series phosphors prepared by high temperature solid state reaction are introduced briefly.XRD analysis results show that the powders contained BaF₂,LiBaF₃,and Ba₄Yb₃F₁₇ crystal phases,and the proportions of the three phases varied with the concentration ratio of Yb³⁺/Er³⁺ions.SEM images show that the powder samples are mainly spherical particles,with an average size of about 55 nm.There are no obvious absorption peaks in the LiBaF₃ matrix,but eight obvious absorption peaks(bands)can be observed after Yb³⁺and Er³⁺incorporation,which belong to the Er³⁺ion transitions from ground state to each excited state and the Yb³⁺ion transition from ~2F_7/2?~2F_5/2 states.Under the excitation of the 980 nm semiconductor laser,the emission spectra of LBF:Yb³⁺,Er³⁺phosphors have five main emission peaks,and the central wavelengths are located at 379,407,522,541,and 652nm,respectively.The energy transfer and transition mechanisms between Yb³⁺and Er³⁺are analyzed in detail based on the schematic diagram of Yb³⁺-Er³⁺energy levels,and the tunable performance of phosphors are discussed.The tunable distance of LBF:20Yb³⁺,0.5Er³⁺samples is up to 0.1618.The variation of emission peak intensity with pump power is studied.Most of the samples showed optical bistability characteristics,and the hysteresis loop area is large.The internal mechanism of the optical bistability is discussed.Secondly,series of Er³⁺,Ho³⁺,Tm³⁺signle-doped KYb(MoO₄)₂ phosphors are designed and prepared.XRD results show that the three series samples belong to the orthorhombic crystal system,and the space group is Pbcn(60).All the phosphors are still composed of spherical particles with an average size of 48 nm.The PL spectra of KYMO:Er³⁺/Tm³⁺/Ho³⁺samples are recorded under 980 nm semiconductor laser excitation.Among them,KYMO:4.0Er³⁺phosphor has two strong green emission peaks,the central wavelength is 520and 541 nm,which contribute to Er³⁺ion ~2H_11/2 and ~4S_3/2?~4I_15/2 transition.In addition,the weak emission peaks also exist at 378,405,489,and 651 nm,which belong to the Er³⁺ion~4G_11/2/~2H_9/2/~4F_5/2/~4F_9/2?~4I_15/2 transition,respectively.For the KYMO:0.6Tm³⁺sample,there is a strong blue emission peak,which is derived from the transitions of the Tm³⁺ion ~1D₂?~3F₄and ~1G₄?~3H₆,and its weak red and near infrared emission belongs to ~1G₄/~3H₄?~3H₆transitions,respectively.KYMO:1.0Ho³⁺phosphors,mainly produces bright red,green emissions and other faint visible light emissions,which belong to the transitions of Ho³⁺ion~5G₄/~3K₇/~5G₅/~3K₈/~5F₃/~5F₄/~5S₂/~5F₅?~5I₈ between energy levels,respectively.Meanwhile,the PL characteristics have been analyzed in depth,and the optimized doping concentrations of Er³⁺,Tm³⁺,and Ho³⁺are 4.0,0.6,and 1.0 mol%,respectively.Finally,the variation of color purity of the three phosphors with pump power are calculated and discussed.