The Down-Conversion Luminescence Properties Of Bi³⁺,Eu³⁺ Doped Oxidesand Aluminate

With the advantages of high chemical stability,long luminescence lifetime,high color purity and multi-wavelength tunable fluorescence emission,down-conversion luminescent materials have a wide range of applications in catalysts,lighting,fluorescent probes,anti-counterfeiting,textiles,etc.Rare earth oxides are broadband semiconductor materials that have attracted interest for their excellent thermal,chemical,electrical,magnetic,ceramic,and optical properties.LaAlO₃as an oxide with an ABO₃type chalcogenide structure,is able to take the place of La³⁺ions when doped with other rare earth ions or transition metal elements,resulting in enhanced luminescence.In this paper,we focuses on the down-conversion luminescence properties of Bi³⁺ions and Eu³⁺ions co-doped oxides,LaAlO₃.（1）A series of Eu³⁺ion-doped Ln₂O₃（Ln=La,Gd and Y）phosphors were synthesized by a high-temperature solid-phase method;the relationships between the crystalline phases of Ln₂O₃（Ln=La,Gd and Y）phosphors,the changes of cation radii and the Eu-O charge migration bands,and their down-conversion luminescence properties were mainly investigated.The XRD test results compared with the standard cards showed that the prepared La₂O₃belonged to the hexagonal crystal system,Gd₂O₃and Y₂O₃belonged to the cubic crystal system.The prepared La₂O₃belongs to the hexagonal crystal system,Gd₂O₃and Y₂O₃belong to the cubic crystal system.In the Ln₂O₃:5 mol%Eu³⁺phosphor,the position of the Eu-O charge migration band is blue-shifted as the radius of rare earth ions decreased(La³⁺:0.106 nm>Gd³⁺:0.094 nm>Y³⁺:0.089 nm),which is related to the distance from the ligand ion(O^2-ion)to the central ion(Eu³⁺ion).All three oxides are dominated by the ⁵D₀→⁷F₂electric dipole leap after doping with Eu³⁺ions,and the Eu³⁺ions occupy the central lattice position without inversion symmetry in the oxide crystal.After 1 mol%Bi³⁺doping into Ln₂O₃:Eu³⁺（Ln=La,Gd and Y）enhanced the luminescence intensity of the phosphor,the excitation peak of Bi³⁺ions and the emission peak of Eu³⁺ions existed partly overlapped,which satisfied the condition of fluorescence resonance energy transfer and proved the existence of energy transfer of Bi³⁺→Eu³⁺.（2）LaAlO₃:x mol%Eu³⁺（x=1,2,3,4 and 5）,LaAlO₃:y mol%Bi³⁺（y=1,2,3,4and 5）LaAlO₃:1 mol%Bi³⁺,x mol%Eu³⁺（x=1,2,3,4 and 5）phosphors were synthesized by high-temperature solid-phase method.The crystalline phases of the phosphors,the down-conversion luminescence properties and the energy transfer process of Bi³⁺→Eu³⁺were investigated.The XRD test results showed that the prepared phosphors LaAlO₃are in rhombic phase.The optimal doping concentrations of LaAlO₃with single doped Eu³⁺ions and single doped Bi³⁺ions are confirmed.The emission spectrum of LaAlO₃:1 mol%Bi³⁺partially overlapped with the excitation spectrum of LaAlO₃:3mol%Eu³⁺,which satisfied the condition of fluorescence resonance energy transfer and proved the energy transfer between Bi³⁺→Eu³⁺.The energy transfer between LaAlO₃:x mol%Eu³⁺（x=1,2,3,4 and 5）phosphor doped with 1 mol%Bi³⁺ions,the color coordinate results show that the luminescence color of the phosphor shifts from orange to red region.The above results indicate that the synthesized LaAlO₃:1 mol%Bi³⁺,x mol%Eu³⁺（x=1,2,3,4 and 5）phosphors are suitable for light emitting diodes（LEDs）and display devices.