Synthesis And Properties Of Rare Earth Ions-doped Tunable Luminescent Phosphors For White Light-emitting Diodes

The fourth-generation environment friendly lighting source（w-leds）has penetrated into the lighting for home and all walks of life with many advantages such as energy saving,environment friendly（Lead-free and mercury-free）,high efficiency and stability,long service life,adjustable light color and color temperature,etc.Among the many white light LED devices,the LED chip+photoluminescent phosphor combination type device has the advantages of high color rendering index,high quantum efficiency,high stability,low cost,and easy assembly,the implementation method of this white light LED device is widely favored and invested by commercial investors.The chip selection and packaging of the white LED devices change with the change of the performance of the phosphors,the performance of the phosphors determines the upper limit of the white LED devices,so it is very important to prepare high-performance rare earth ion activated phosphors for the white LED.Nowadays,the research of single-matrix phosphors doped with rare earth ions has tended to be saturated.Therefore,this article shifts the focus of research to improve the performance of existing phosphors,and it will using different alkaline earth metal ions to partially replace different alkaline earth metal ions,or designing solid solution phosphors to improve the luminescence performance of phosphors.This article prepared three different phosphor systems that can be excited by（near）UV or blue LED chips,and analyzed and discussed their transitions in luminous properties in detail through a variety of characterization methods.1.A series of emitting color adjustable Eu²⁺-activated Na Ca_9.99-xSr_x（PO₄）₇:0.01Eu²⁺solid solution phosphors withβ-Ca₃（PO₄）₂ phase were successfully synthesized via a sol-gel method.X-ray diffraction（XRD）and normalized emission spectrum show that the two components of this phosphate phosphor have been fused into a solid solution.And when the concentration of Sr²⁺is x=7,the solid solution is closest to the critical point of phase transition,and it undergoes phase transition from R3c?R-3m.There are four cation sites that can be occupied by Eu²⁺in phosphors withβ-Ca₃（PO₄）₂ phase.The changes in the concentration of Sr²⁺changed the distribution of Eu²⁺among the points.Under the excitation of ultraviolet light（288 nm）,the luminous color of the solid solution phosphor has undergone the process of tuning from sky blue to yellow green and finally tuning from yellow green to dark blue;With a fixed Ca²⁺/Sr²⁺ratio,the luminous color of the phosphor can gradually change from yellow-green to yellow as the wavelength of the excitation light increases.2.A series of（Sr,M）₂MgSi₂O₇:Eu²⁺（M=Mg,Ca,Ba）phosphors were synthesized by a sol-gel method.The X-ray diffraction（XRD）pattern shows that the proper introduction of different alkaline earth metal ions in host would not damage the matrix lattice structure.There is only one Mg²⁺lattice with a coordination number of 4 in Sr₂MgSi₂O₇,and Eu²⁺and other alkaline earth metal ions cannot enter this site.When Mg²⁺with a relatively small radius was introduced,the position of the XRD diffraction peak did not move,and the position of its emission peak did not change,indicating that Mg²⁺did not replace Eu²⁺,but repaired the lattice defect.When Ca²⁺/Ba²⁺with a relatively small/large radius is used instead of Sr²⁺,the XRD diffraction peaks move to high/low angles,respectively,and their emission peaks undergo red/blue shifts,this indicates that the introduction of Ca²⁺/Ba²⁺changed the crystal field intensity around the light-emitting center,etc.,and achieved light blue/dark blue emission.3.A series of Lu_2.94(Al_5-2xMg_xSi_x)O₁₂:Ce³⁺solid solution phosphors with garnet structure were synthesized by a sol-gel method.This article have studied the X-ray diffraction pattern（XRD）,normalized emission spectrum of this solid solution phosphor,and compared the relevant literature,the results show that the two components of this phosphate phosphor have been fused into a solid solution.Using Mg²⁺-Si⁴⁺ion combination replace the Al³⁺-Al³⁺ion of the[Al O₆]octahedron and[Al O₄]tetrahedron in the Lu AG lattice,it still maintains the garnet configuration.The[Al O_X]polyhedron distortion in the second coordination domain leads to the compression of the[Ce O₈]polyhedron as a whole,this phenomenon caused the site differentiation and symmetry reduction of the luminous center,and its luminous color shifted from green to red to yellow.By using Mg²⁺alone instead of Al³⁺,the reason for the different broadening directions of its excitation peak and emission peak was proved by experimental results.While the emission spectrum is widened and red-shifted,a strong broadening of the excitation peak is also observed.Due to its excellent light emitting properties,the Lu_2.94(Al_5-2xMg_xSi_x)O₁₂:Ce³⁺solid solution phosphor prepared in this paper has potential application value in warm WLEDs.