Preparation And Luminescence Properties Of Eu³⁺Doped Red Phosphor For White LED

Due to high color rendering and adjustable color temperature,the method of"near-ultraviolet LED chips(380-410 nm)+ trichromatic phosphors" for generating white light has generally replaced the method of"blue LED chips + YAG:Ce3+ phosphor",and become a new solution for white light LED illumination.The Eu3+ doped red phosphor based on the 4f-4f transition can be excited by near-ultraviolet light,and its fluorescence wavelength is mainly concentrated near 615nm,which has the characteristics of narrow emission band and high color purity.Therefore,the Eu3+ doped red phosphor is in good agreement with the requirements of this new method.However,due to the spin-forbidden nature of the 4f-4f transition,absorption at the near-ultraviolet wavelength and emission at red wavelength of the Eu3+ doped phosphor are both weak.In order to solve this problem,tow kinds of novel phosphors in which the high Eu3+ doping concentration can be realized were prepared in this work.Then,the red luminescence properties of the phosphors excied by the near-ultraviolet light were investigated.A series of LiGd3(1-x)Eu3,(MoO4)5(LGM:xEu3+,x=0,10,20,…,100at.%)red phosphors were synthesized by solid-state reaction method,and their structure and spectroscopic properties were investigated.Under excitation at 395 nm,red luminescence at 615 nm was observed in the LGM:xEu3+ phosphors,which corresponds to the 5D0→7F2 transition of Eu3+,and the optimal Eu3+ concentration is 90at.%in the phosphors.The emission intensity of 5D0→7F2 transition of the LGM:90at.%Eu3+ phosphor is approximate 2.5 times of that of the Y2O2S:6.3at.%Eu3+ commercial phosphor.The internal quantum efficiency of the LGM:90at.%Eu3+ phosphor is 41%.The chromaticity coordinate of the LGM:90at.%Eu3+ phosphor is(0.6705,0.3292),which is close to the standard red chromaticity(0.67,0.33),and the color purity of the LGM:90at.%Eu3+ is close to 100%.Furthermore,the LGM:90at.%Eu3+ phosphor has good thermal stability.When the temperature was increased to 475 K,the emission intensity corresponding to SD0→7F2 transition of the phosphor was decreased to 54%of the initial value at 300 K.Above results indicate that the LGM:90at.%Eu3+ is a promising red phosphor that can be efficiently excited by NUV LED chips.A series of KBaYi1-xEuxSi2O7(KBYS:xEu3+,x=0,10,20,...…,100at.%)red phosphors were also synthesized by solid-state reaction method,and their structure and spectroscopic properties were investigated.Under excitation at 394 nm,red luminescence at 610 nm was observed in the KBYS:xEu3+ phosphors,which corresponds to the SD0→7F2 transition of Eu3+,and the optimal Eu3+ concentration is 80at.%in the phosphors.The emission intensity of 5D0→7F2 transition of the KBYS:80at.%Eu3+ phosphor is approximate one-sixth of that of the Y2O2S:6.3at.%Eu3+ commercial phosphor.The internal quantum efficiency and chromaticity coordinate of the KBYS:80at.%Eu3+phosphor is 58%and(0.6705,0.3292),respectively.Moreover,the KBYS:80at.%Eu3+phosphor has excellent thermal stability.When the temperature was increased to 748 K from room temperature,the emission intensity corresponding to 5D0→7F2 transition of the phosphor was only declined by 9%.Finally,the crystal structure and emission intensity of the KBYS:80at.%Eu3+ and LGM:90at.%Eu3+ phosphors were compared.These two kinds of structure are both beneficial to achieve the high Eu3+ doping concentration in the phosphors,and the stronger emission of the 5D0→7F2 hypersensitive transition can be realized in the Eu3+ doped LGM phosphor.