The Luminescence Properties Of Eu-doped Aluminosilicate For W-LED

Environmental problems have become more and more serious since 21 century.In order to reduce the pollution to the environment and to solve the problem of temperature increasing,researchers have actively sought to replace the currently used fossil fuels that polluting the environment.White light emitting diode?w-LED?,as the new generation lighting source,is considered to be an excellent lighting source to replace the existing conventional fluorescent lamps and incandescent lamps because of its outstanding advantages,such as low power consumption,long operating life,good stability of physical and chemical properties and special mercury-free characteristics.Therefore,the manufacture and improvement of w-LEDs have become an important and urgent topic.In order to make the w-LEDs have excellent performance,the phosphor used must be optimized,so the focus of current research is to prepare phosphors with good thermal stability and high luminescence efficiency.W-led fabricated by combining YAG:Ce³⁺with InGaN chip is the most widely used.However,because of the defect of red light,the related color temperature?CCT,Tc>5500 k?is higher and the color index?CRI,Ra<80?is low.For the whole w-LED system,due to the complexity of fabrication,the reabsorption of emission color and the different aging rate of each kind of phosphor,there are several shortcomings,such as high cost and low luminous efficiency.Therefore,the development of a single-phase white emission phosphor which can effectively excited by ultraviolet light is the root to improve the luminous efficiency and improve the CRI.In this paper,a series of Eudoped apatite silicate phosphors were designed and synthesized by high temperature solid solution.The samples were characterized by XRD,photoluminescence properties,decay curves and thermal stability spectra.The crystal structure,luminescence properties,decay lifetime and the energy transfer were analyzed in detail.The main results are as follows:?1?A series of aluminosilicate phosphors CaLa₉?AlO₄??SiO₄?₅O₂:xEu?x=0.005,0.01,0.02,0.04 and 0.05?,SrLa₉?AlO₄??SiO₄?₅O₂:xEu?x=0.02,0.03,0.04,0.08,0.1?,BaLa₉?AlO₄??SiO₄?₅O₂:xEu?x=0.04,0.06,0.08,0.1?have been synthesized through high temperature solid phase method.The samples were characterized by XRD.Upon320 nm excitation,the emission spectra of these samples were measured.Measured the decay lifetime of BaLa₉?AlO₄??SiO₄?₅O₂:0.04Eu and BaLa₉?AlO₄??SiO₄?₅O₂:0.06Eu and through the decay lifetime the truth that the host has two luminescence centers was proved.The energy transfer mechanism in this type of phosphor is calculated as the dipole-dipole interaction.The thermal stability of the phosphors of the three kinds of phosphors was tested.With the increase of the temperature,the emission intensity of the three phosphors decreased,but the thermal stability was still excellent.The activation energy of CaLa₉?AlO₄??SiO₄?₅O₂:0.02Eu is calculated to be 0.3795 eV and SrLa₉?AlO₄??SiO₄?₅O₂:xEu is 0.2389 eV.Due to the difference of the coordination environment around the luminescence center,the optical properties of the three is also slightly different,but on the whole,the synthesized samples have more stable luminescence and better thermal stability.?2?According to the study of the first part,choose the SrLa₉?AlO₄??SiO₄?₅O₂:xEu phosphors which have a better performance in optical properties,replace the La³⁺with Y³⁺,Lu³⁺and Sc³⁺to prepare SrA₉?AlO₄??SiO₄?₅O₂:xEu?A=Y,Lu,Sc?phosphors with apatite structure.The phosphors were prepared by conventional high temperature solid state reaction.The structural of the sample was determined by XRD.The excitation and emission spectra of the matrix sample were tested which show that as-prepared phosphors were practical.The optimum doping concentrations of SrY₉?AlO₄??SiO₄?₅O₂:xEu and SrSc₉?AlO₄??SiO₄?₅O₂:xEu were x=0.06 and 0.05,respectively.The energy transfer mechanism in this type of phosphor is calculated as the dipole-quadrupole interactions.The prepared SrSc₉?AlO₄??SiO₄?₅O₂:xEu showed excellent thermal stability compared with the other two matrices.The activation energies of SrLu₉?AlO₄??SiO₄?₅O₂:0.05Eu and SrSc₉?AlO₄??SiO₄?₅O₂:0.05Eu were calculated to be 0.2635 eV and 0.2697 eV,respectively.?3?On the basis of the first two parts,the relative contents of Sr²⁺and Y³⁺and the relative contents of?AlO₄?and?SiO₄?anionic groups in the original SrY₉?AlO₄??SiO₄?₅O₂:xEu?A=Y,Lu,Sc?phosphors were changed to prepare the new type of phosphor Sr₄Y₆?AlO₄?_x?SiO₄?_6-xO_?1-x/2?:yEu and choose Sr₄Y₆?AlO₄?₂?SiO₄?₄:yEu?y=0.005,0.02,0.04,0.05,0.06,0.08?as an example.The samples were characterized by XRD.Measured the decay lifetime and emission spectrum,through the decay lifetime the truth that the host has two luminescence centers was proved.The energy transfer mechanism in this type of phosphor is calculated as the dipole-dipole interactions.The crystal field theory is used to explain the phenomenon that under the excitation of 338 nm,the emission peak position of Sr₄Y₆?AlO₄?₂?SiO₄?₄:yEu?y=0.005,0.02,0.04,0.05,0.06,0.08?samples have red-shifted with the doping concentration.The thermal stability of the Sr₄Y₆?AlO₄?₂?SiO₄?₄:0.06 Eu sample was tested.At 150?,the luminescence intensity decreased by only 28.15%compared with room temperature,indicating that this type of phosphor has better thermal stability.In this paper,three types of Eu-doped aluminosilicate phosphors have been synthesized.The prepared phosphors have good optical properties and have a certain reference for the study of phosphors of aluminosilicate matrix.