Synthesis And Luminescence Properties Of Novel Phosphate Phosphors For White LED Application

White LED based on near ultraviolet（n-UV）chip excitation of red,green and blue（RGB）phosphor has the advantages of high color rendering index（CRI）and adjustable correlated color temperature（CCT）,which is an important development direction at the present.It has been reported that the thermal quenching effect of phosphors is widespread,which limits the development and application of white LED devices.In recent years,with the development trend of high-power LED devices,it is very important to explore new phosphors with high light efficiency and thermal stability.Among phosphor hosts,phosphates have attracted extensive attention due to their extensive sources,simple preparation,low energy consumption and stable physical and chemical properties.In this thesis,different types of phosphate substrates（orthophosphates,metaphosphates and pyrophosphates）were investigated by solid solution design and high-temperature solid-state synthesis of phosphors were explored.The luminescence properties of Eu²⁺doped phosphors were regulated and optimized by structural regulation.The main research findings are as follows:（1）A blue emission RbCaPO₄:Eu²⁺phosphor was synthesized and its crystal structure and fluorescence properties were studied.The crystal structure of RbCaPO₄:Eu²⁺phosphore belongs to monoclinic system,the space group is P2₁/m,the optimal excitation wavelength is303 nm,the emission peak is located at 452 nm,and the optimal doping concentration of Eu²⁺is 1.3%.Eu²⁺doping concentration has a certain effect on the thermal stability of phosphors.When the doping concentration is 0.5%,zero thermal quenching can be achieved at 250℃.With the increase of doping concentration,the thermal stability decreases due to the increase of lattice distortion.In addition,the effects of adding excessive Rband cationic solution substitution on the luminescence properties of phosphors were also studied.The results show that the thermal stability and internal and external quantum efficiency of phosphors are significantly improved when Rbexceeds 10%～40%.The amount of Rb⁺substituted by K⁺solution is up to 30%,and all of them have excellent zero thermal quenching performance.The fluorescent powder and commercial green and red phosphors are packaged into an n-UV chip excited white LED device with high CRI and adjustable CCT.（2）A novel K₂Sr（PO₃）₄:Eu²⁺phosphor emitting ultra-narrowband bluish violet light was reported.Its crystal structure and fluorescence properties were studied.The crystal structure of K₂Sr（PO₃）₄:Eu²⁺phosphor is tetragonal,the space group is I-4,the optimal excitation wavelength is 334 nm,the emission peak is 416 nm,the full width at half maximum（FWHM）is 21 nm,and the optimal doping concentration of Eu²⁺is 2.5%.When the doping concentration is lower than 2.5%,the color purity of the phosphor increases and FWHM decreases with the increase of the doping concentration.When the doping concentration is higher than 2.5%,the color purity of the phosphor decreases and FWHM increases with the increase of the doping concentration.In addition,the luminescence intensity of K₂Sr（PO₃）₄:Eu²⁺phosphor decreases significantly with the increase of temperature,which demonstrates its sensitivity to temperature and is expected to be applied in the field of high-sensitivity fluorescence temperature sensing.（3）Rb₂Ca_1-xSr_xP₂O₇:Eu²⁺phosphors were prepared by solid solution substitution strategy,and their fluorescence heat quenching resistance was optimized.It was found that the maximum solution limit of Ca²⁺and Sr²⁺was 80%（x=0.8）,and with Sr²⁺gradually replacing Ca²⁺,the emission peak position gradually shifted blue,and the luminescence gradually changed from orange to yellow.When 20%Sr²⁺（x=0.2）was introduced into the Caposition in Rb₂CaP₂O₇:Eu²⁺solution,the integral intensity of the sample phosphor at 150℃increased by 64%compared with Rb₂CaP₂O₇:Eu²⁺phosphor.Rb₂Ca_0.8Sr_0.2P₂O₇:Eu²⁺orange phosphor,commercial blue and green phosphors were packaged into an n-UV chip excited white LED device with high CRI and adjustable CCT.