Synthesis And Luminescence Of Rare Earth Doped Ca₃Gd?AlO?₃?BO₃?₄ Phosphors For White Light-Emitting Diodes

White light-emitting diode?LED?can replace the traditional lighting source?incandescent lamp and fluorescent lamp?as a new generation of solid lighting source,with a long life,less energy consumption,easy repair,environmentally friendly and easy to control and other advantages.However,there are some problems of commercial WLEDs(blue LED chip+Y₃Al₅O₁₂:Ce³⁺yellow phosphor),such as the low CRI and high CCT caused by the lack of red light,and the decline of white light quality caused by the aging process of blue light LED chip.In order to solve these problems,the research scheme of red,green and blue phosphors excited by ultraviolet LED chip is proposed.Compared with the blue light-activated WLED,the color of the ultraviolet-activated WLED is totally determined by the red,green and blue phosphors,which not only improves the CRI,but also can obtain high-quality white light with stable color.Therefore,it is very important to develop efficient red,green and blue phosphors that can be excited by ultraviolet LED chips.In this paper,Ca₃Gd?AlO?₃?BO₃?₄ was used as the host to study the luminescence properties of Eu³⁺,Tb³⁺,and Ce³⁺,Tb³⁺doped systems,and analyze their structure,excitation spectrum,emission spectrum and energy transfer.In the first chapter of this paper,the research background of WLEDs phosphors,host materials and properties are briefly summarized.Chapter 2-5 introduce the experimental scheme,characterization methods and applications of WLED,respectively.The emphasis is divided into the following aspects:?1?The luminescent properties of Eu³⁺in Ca₃Gd?AlO?₃?BO₃?₄ were studied.Firstly,Ca₃Gd?AlO?₃?BO₃?₄:Eu³⁺red phosphors were synthesized by high temperature solid state reaction.It is found that Ca₃Gd?AlO?₃?BO₃?₄:Eu³⁺can be effectively excited in the ultraviolet region,with the best excitation peak at 397 nm and the best emission peak at 621 nm.The optimal sample Ca₃Gd?AlO?₃?BO₃?₄:0.5Eu³⁺was found to have good thermal stability?the luminescence intensity at 150?is 84%of that at room temperature?and internal quantum efficiency as high as 90%.Compared with the commercial red phosphor Y₂O₃:Eu³⁺,the CIE coordinates of Ca₃Gd?AlO?₃?BO₃?₄:0.5Eu³⁺was more closer to ideal red light.Finally,a WLED with CIE=?0.322,0.374?,CRI=73.1,CCT=5900Kwasmadebycombiningtheredphosphor Ca₃Gd?AlO?₃?BO₃?₄:0.5Eu³⁺,commercial blue phosphor BAM:Eu²⁺,commercial green phosphors?Ba,Sr?₂SiO₄:Eu²⁺and 395 nm near ultraviolet LED chips.?2?Ca₃Gd?AlO?₃?BO₃?₄:Tb³⁺,Eu³⁺phosphors were prepared by high temperature solid phase method.Their X-ray diffraction,luminescence properties under ultraviolet excitation and energy transfer mechanism of Tb³⁺?Eu³⁺phosphors were discussed in detail.The emission spectra of Ca₃Gd?AlO?₃?BO₃?₄:Tb³⁺,Eu³⁺phosphors showed green light from Tb³⁺and red light from Eu³⁺under the excitation at 352 nm.By analyzing the excitation and emission spectra of a series of samples with different concentrations,the energy transfer of Tb³⁺?Eu³⁺in the Ca₃Gd?AlO?₃?BO₃?₄ does exist and could be realized by the way of quadrupole-quadrupole interaction.Based on Tb³⁺?Eu³⁺,we not only can adjust the concentration rate of Eu³⁺/Tb³⁺to obtain different color,and also enhance the Eu³⁺absorption in ultraviolet region by doping sensitizer Tb³⁺ions.Finally,a WLED with CIE=?0.369,0.381?,CRI=85.3,CCT=4329 K was made by combining the red phosphor Ca₃Gd?AlO?₃?BO₃?₄:0.5Tb³⁺,0.1Eu³⁺commercialbluephosphor BAM:Eu²⁺,commercial green phosphors?Ba,Sr?₂SiO₄:Eu²⁺and 365 nm near ultraviolet LED chips.?3?Ca₃Gd?AlO?₃?BO₃?₄:Ce³⁺,Tb³⁺multi-color phosphors were synthesized and their luminescence properties under ultraviolet excitation at 347 nm and 370 nm were tested.By studying the relationship of lifetimes of Ce³⁺and Tb³⁺concentration in Ca₃Gd?AlO?₃?BO₃?₄:Ce³⁺,Ca₃Gd?AlO?₃?BO₃?₄:Ce³⁺,Tb³⁺,the energy transfer of Ce³⁺?Tb³⁺in the Ca₃Gd?AlO?₃?BO₃?₄ was confirmed at 347 nm excitation.By increasing Tb³⁺/Ce³⁺concentration ratio,light of Ca₃Gd?AlO?₃?BO₃?₄:Ce³⁺,Tb³⁺can transfer from blue region to the green region,and then obtained a green phosphor Ca₃Gd?AlO?₃?BO₃?₄:0.01Ce³⁺,0.6Tb³⁺with internal quantum efficiency of 38.2%.Finally,a WLED with CIE=?0.427,0.401?,CRI=79.7,CCT=3158 K was prepared by combining red phosphor CaAlSiN₃:Eu²⁺,commercial blue phosphor BAM:Eu²⁺,green phosphor Ca₃Gd?AlO?₃?BO₃?₄:0.01Ce³⁺,0.6Tb³⁺and 365 nm LED chips.