Preparation And Luminescence Properties Of Rare Earth Composite And Yttrium Substituted Yttrium Sodium Tungstate Microcrystals

It is well known that local environment and microstructure regulation,as one of the most important means to improve the properties of matrix materials,has been proved to be feasible and promising.As a derivative of scheelite,the compound alkali metal yttrium sodium tungstate is a representative of disordered crystal,whose cell structure is basically the same as Ca WO₄,which is uniaxial crystal and tetragonal crystal system.Therefore,its lattice structure is characterized by random and short order distribution of Na⁺ions and Y³⁺ions,and it is often used as a substrate luminescent material to carry out doping tests of rare earth ions with different concentrations.Taking yttrium tungstate sodium-based rare earth luminescent materials as the research object,the internal relationship between the structure and fluorescence properties of the materials was studied by introducing trivalent La ions into the crystal structure and corresponding fluorescence properties of the equivalent yttrium-substituted materials.In this paper,La³⁺and Eu³⁺co-doped NaY（WO₄）₂microcrystals were prepared.Due to the introduction of La³⁺ions,the lattice spacing of the sample increases and the length of W-O bond increases.Moreover,when La³⁺ions completely replace Y³⁺ions,the band gap of the main material increases from 4.44 e V to 4.51 e V.In addition,with the increase of La³⁺ion doping concentration,the emission peak of Eu³⁺red light increases first and then decreases,and the optimal doping concentration is 0.6.At this time,the sample has 47.38%quantum efficiency and pure red emission,and the final packaged LED device obtains bright positive white light.After that,La³⁺doped microcrystals in NaY（WO₄）₂:Dy³⁺matrix were prepared successfully.Due to the introduction of La³⁺ions,the local symmetry around Dy³⁺is changed,resulting in the characteristic transition of Dy³⁺showing obvious concentration quenching phenomenon.When the concentration of La³⁺ion is 0.4,the yellow luminescence is the strongest and the color coordinate is（0.4224,0.4600）.Meanwhile,it also has good thermal stability.In addition,this paper explores the energy transfer mechanism of the sample under different excitation light states.Finally,La³⁺doped NaY（WO₄）₂:Tb³⁺matrix microcrystals were prepared.Similarly,with the doping of La³⁺ions,Tb³⁺characteristic luminescence showed a concentration quenching phenomenon,and the optimal doping ratio was 0.6.At this time,the PLQY of the sample reached 54.87%,and the color purity of green luminescence was the highest.