Fabrication and Properties of Rare Earth Phosphors and Their Applications in White-light LEDs

Three types of white-light LEDs consisted of blue LED chip and YAG phosphor,blue LED chip,YAG and red blue LED chip,green and red phosphor were fabricated.Their CIE parameters were also mearsued under 20 mA DC driving.The CIE coordinates are (0.326,0.339),(0.326,0.339),and(0.324,0.324);the correlated color temperature T_c are 5 781,5 627,and 5 937 K;and the color-rendering index Ra are 82.3,86.2,and 92.2,respectively.It shows that the adding of red light into the white light will improve the quality of the white light.The different DC driving,increasing of the current from 5.0 mA to 60 mA,results in higher color temperature T_c and lower color rendering index.It was found that the red saturated when the current was higher than 30 mA.The phosphors(M_1,M_2)_(10)(PO_4)_6X_2(M_1=Ca,Sr,Ba;M_2=Eu,Mn;X=F,Cl,Br) have been synthesized in reductive atmosphere at 900～1 200 ℃ for 2.0～8.0 h.The phosphors with different compositions give the emission at 455,477,500,and 580 nm when excited by 400 nm near light.Three types of white LEDs were fabricated using LED chips and the phosphors mentioned above.The constitutions are UV LED chip,blue phosphor,and YAG phosphor,UV LED chip,blue and red UV LED chip,blue phosphor,green and red phosphor.Their CIE coordinates are(0.303,(0.329)),(0.327,0.328),and(0.331,0.333);the correlated color temperature T_c are 7 070,5 747,(5 566) K;and the color-rendering index Ra are 79.2,80.4,and 87.9 under 20 mA DC driving,respectively.The different DC driving,increasing of the current from 5.0 mA to 60 mA result in a higher color temperature T_c and a lower color rendering index.However,CIE coordinate of the white light LED consisted of LED chip,blue and YAG changed the least.