Study On Upconversion Luminescence Properties Of Modified Rare Earth Doped Yttrium Sodium Molybdate

At present,red phosphor plays a very important role in white LED lighting devices and is the key material to improve the color rendering index of lighting sources.The rare earth doped molybdate red phosphor has attracted much attention because of its outstanding stability and luminescent characteristics.However,in recent years,the research on rare earth doped molybdate mainly focuses on the synthesis method and the influence of rare earth ion concentration on its phase composition and luminescent performance.However,the upconversion luminescent intensity of rare earth doped molybdate is generally very low.How to improve the upconversion luminescent intensity of rare earth doped yttrium sodium molybdate is worth studying.It is found that the metal ions doping can improve the luminescent efficiency of vanadate and phosphate phosphors.The purpose of this paper is to introduce this method into the study of molybdate luminescent materials,and to study and discuss the luminescent properties of the materials by adding SiO₂ microspheres and nano molybdate up conversion luminescent materials to form core-shell structure.Yb³⁺ has strong absorption at 980 nm as a sensitizer,and water molecules also absorb at 980 nm.The two absorption bands overlap,which can cause the overheating reaction of organism,thus leading to serious tissue damage and cell death.The results show that the more biocompatible 800 nm excitation light can avoid this phenomenon.Sm³⁺ can generate up conversion luminescence under 814 nm excitation light.How to improve the luminous intensity of Sm³⁺ is the focus of the research.Through consulting the literature,doping different rare earth ions or alkaline earth ions can enhance the fluorescence efficiency and provide a broader prospect for its application.Mg2 +,Ba2 +,Sr2 + and Ca2 + can damage the long molecular chain,which will affect the optical properties of upconversion luminescence.The purpose of this paper is to improve the intensity of Sm³⁺ upconversion luminescence under 814 nm excitation light by doping alkaline earth divalent metal.The specific research contents are as follows: 1.A series of NaY?MoO₄?₂: Eu³⁺@SiO₂ upconversion luminescent material were prepared by hydrothermal method.The discussion of structure and luminous properties of the samples were analysed by x-ray diffraction?XRD?,Scanning electron microscope?SEM?,energy spectrometer?EDS?,Infrared spectrum?FR?,fluorescence?FL?spectrum etc.The results indicated that the diffraction peak positions of the SiO₂ core-shell structure samples are consistent with standard pattern of NaY?MoO₄?₂: Eu³⁺ at characteristic diffraction peaks and impurity diffraction peaks did not appear at all;The morphology of NaY?MoO₄?₂: Eu³⁺@SiO₂ is a core-shell structure.NaY?MoO₄?₂: Eu³⁺ is coated on the surface of SiO₂ microspheres and obtain micro-spheres.It can be known that the Y³⁺ lattice positions were taken place by Eu³⁺ from analysis of EDS and XRD;the Si-OH bond in the SiO₂ microsphere can band the metal ion together.Under near-infrared light excitation at 793 nm,the NaY?MoO₄?₂: Eu³⁺@SiO₂ samples exhibited red emission at 616 nm.The luminescence intensity of NaY?MoO₄?₂: Eu³⁺@6.2SiO₂ is about 3 times stronger than NaY?MoO₄?₂: Eu³⁺.2.Different kinds of alkaline earth metal ion Re²⁺(Mg²⁺?Ba²⁺?Sr²⁺?Ca²⁺)doping NaY?MoO₄?₂:Sm³⁺ upconversion fluorescent material were synthesized by hydrothermal method,through Xray powder diffraction,Scanning electron microscope?SEM?,emission spectrum were used to characterize the crystal structure,morphology and upconversion luminescent properties of the synthesized samples.The results show that the doping of alkaline earth metals can enter the matrix lattice through Y³⁺lattice and occupying the lattice gap.For NaY?MoO₄?₂:Sm³⁺,a green emission peak at 565 nm,an orange emission peak at 600 nm and a red emission peak at 647 nm appear under 814-nm excitation,which results from the energy level transition of 4G5/2?6H5/2?4G5/2?6H7/2?4G5/2?6H9/2.the phase of Re²⁺@NaY?MoO₄?₂:Sm³⁺ after doping alkaline earth metal ions is consistent with NaY?MoO₄?₂ standard card.The morphology is more uniform.After doping Re²⁺(Mg²⁺?Ba²⁺?Sr²⁺?Ca²⁺),the luminescence increased about 60%?70%?45%?60%.This is because the doped Re²⁺ ion replaces the Y³⁺ ion to produceO₂-vacancy,Which is used as asensitizer to transfer up conversion energy to the activated ion under the charge transfer coupling.