Preparation And Photoluminescence Properties Of Rare Earth Ions Doped BaZrO₃ And LaOF Phosphors

As a kind of important inorganic materials,rare earth doped BaZrO₃ and LaOF luminescent materials have attracted much attention in the frontier fields of luminescent pigments,phosphors for LED lamps,communication signals,anti-counterfeiting and medical biology due to their good thermal and chemical stability and excellent optical properties.At present,there are many studies on the luminescent properties of rare earth doped BaZrO₃ and LaOF luminescent materials,but there are still some problems to be solved:for example,the intrinsic relationship between defect luminescence and rare earth ion transition luminescence in rare earth doped BaZrO₃ luminescent materials is ambiguous;The comparative study of the different effects of the two kinds of LaOF crystals on the relative luminous properties is insufficient,and its multicolor tunable luminescence needs to be further enriched.In view of this,this work is based on the preparation of Sm³⁺,Tb³⁺,Tm³⁺rare earth ions mono-doped or co-doped BaZrO₃ and LaOF phosphors by hydrothermal assisted solid-state method.The phase structure,particle morphology and luminescence characteristics of the obtained products are characterized by relevant detection methods.The purpose is to discuss the optimal process conditions under the constraints on multiple factors such as hydrothermal time and reaction temperature,and to prepare the most favorable matrix materials for luminescence,by adjusting the calcination temperature and the doping amount of the activator,we can further grasp the photo luminescence performance and energy transfered mechanism of the material,which is of positive significance to broaden its application of LED luminescence,anti-counterfeit identification and other fields.The main contents of this paper are as follows:（1）The optimum process parameters of BaZrO₃ and LaOF substrates were determined by adjusting hydrothermal conditions and calcination temperature,which lays the foundation for the next step of rare earth activated ion doping.First of all,BaZrO₃ hollow microspheres with good morphology and dispersion were prepared under the effect of 14 mol·L^-1 KOH,hydrothermal treatment at 180°C for 24 h,and the dual effects of alkali erosion and Ostwald aging mechanism.Due to its oxygen defect structure which can emit blue light under 255 nm excitation.The crystallinity of BaZrO₃ powder is getting better and better after the calcination at different temperatures,but with the decrease of oxygen defect concentration after calcination,the luminous intensity is gradually weakened.In addition,La CO₃F and La F₃precursors prepared by hydrothermal method were calcined at different temperatures.La CO₃F was calcined at 600°C and 1000°C,and La F₃ was calcined at 900°C and 1000°C to obtain tetragonal and rhombohedral crystalline LaOF matrix materials,respectively.（2）BaZrO₃ phosphors doped with Tb³⁺,Tm³⁺and Sm³⁺were synthesized by hydrothermal method,and their microscopic morphology is still a sphere of relatively uniform particle size distribution.It was characterized by XRD,TEM,IR and fluorescence spectra.The results showed that the rare earth ions entering the BaZrO₃ lattice did not replace the Zr ions at the B position equivalently,resulting in the matrix lattice distortion,and the three kinds of single-doped phosphors had good luminescence properties,especially the Tm³⁺doped BaZrO₃ phosphor because the transition emission peak overlapped with the defect emission peak,and the color purity was as high as 83.73%.In addition,the dominant mechanism of defect luminescence in rare earth doped BaZrO₃ phosphor is described,and the intermediate role of defect energy level in BaZrO₃ rare earth phosphor is determined.（3）A series of Sm³⁺mono-doped LaOF phosphors with different crystal phases were synthesized by hydrothermal assisted high-temperature solid-state method.Through the characterization of their luminescent properties,it was determined that the Sm³⁺mono-doped tetragonal LaOF phosphors prepared with La F₃ as precursor at 900°C had the best luminescent properties,and the best doping concentration was 3.0 mol%.Based on the theoretical model proposed by Judd-Ofelt,the radiative transition parameters of the two crystalline LaOF matrices,the radioactive transition intensity parameters of Sm³⁺ions and the fluorescence branching ratio were obtained,which confirmed that the tetragonal LaOF phosphors had a large fluorescence transition probability,low local symmetry and the strongest luminescence intensity.Through experiments,it was found that the prepared Sm³⁺mono-doped tetragonal LaOF phosphor had a very high color purity,with an average value of more than 99%.Its energy transfer mechanism was the electric dipole-electric dipole interaction in the electric multipole interaction,which could achieve good orange red light emission.（4）Tetragonal LaOF phosphors doped with Tb³⁺,Tm³⁺,Sm³⁺and co-doped with Tb³⁺were synthesized by hydrothermal assisted high temperature solid phase method.The results showed that the single-doped phosphors had high color purity,which laid the foundation for further realizing the control of co-doped polychromatic luminescence.On the one hand,by characterizing the luminescent properties of LaOF:Sm³⁺,Tb³⁺and LaOF:Sm³⁺,Tm³⁺and Tb³⁺phosphors,it is demonstrated that there is a phenomenon of energy transfer from Tb³⁺to Sm³⁺and Tb³⁺,Sm³⁺to Tm³⁺in the system.Based on the classical theories of Blasse,Dexter and Reisfeld,it is determined that the electric dipole-electric dipole interaction in the multipole interaction is the main mechanism that affects its energy transfer.On the other hand,by adjusting the doping ratio and excitation wavelength of rare earth ions,the multicolor luminescence performance of the two phosphors has been successfully achieved.It is further confirmed by experiments that LaOF:2.5 mol%Tm³⁺,3.0 mol%Tb³⁺,3.0 mol%Sm³⁺phosphors can realize LED white light emission under the excitation of commercial ultraviolet light at the wavelength of 365 nm,and the co-doped phosphors of 3.0 mol%Sm³⁺and 3.0 mol%Tb³⁺have good practical application value in fingerprint detection and anti-counterfeiting identification.