| White light-emitting diodes(WLEDs)have attracted much attention for their energy-saving,green,and high-efficiency characteristics,and become an important candidate for the fourth generation of solid-state light sources.In order to achieve higher photoelectric conversion efficiency,the mainstream way of white light illumination is the light conversion type of chip excitation phosphor,its luminous color and use performance are largely influenced by the phosphors’optical performance.The energy transfer,crystal field strength,and covalence of the luminescent center in phosphors are affected by the host’s crystal structure.Therefore,the change in crystal structure will affect its luminous efficiency,luminescence color,and intensity.In this paper,the 4f-4f transitions of Dy3+ions and Eu3+ ions,which are extremely sensitive to the local environment,are used as the regulation mode.The luminescence performance is mainly regulated by the local symmetry-luminescence performance structure-activity relationship.The main research contents and results are as follows:(1)The double perovskite structure BaLaLiWO6:Dy3+,Eu3+single-host white luminescent phosphor was designed and prepared,the doping of Dy3+ions and Eu3+ ions would improve the local symmetry of the occupied lattice,and a local symmetry change model of the A position was established based on the supersensitivity transition characteristics of the two ions.The warm white light emission with color coordinates of(0.382,0.373)can be realized in the BaLaLiWO6:0.04Dy3+,yEu3+co-doped system by the electric dipole-electric dipole interaction energy transfer of Dy3+-Eu3+,and the transfer efficiency can reach 96.31%.Phosphors have a good thermal stability,its emission intensity is still have 92.3%at 200℃,demonstrating excellent thermal quenching resistance of this structure.(2)The B-position cation substitution in BaLaLiWO6:Eu3+ red phosphor was designed to study the effect of its structural changes on luminescence performance.The Na+ions replacing the Li+ions at position B1 causes the expansion of the crystal lattice,thereby enhancing the charge migration excitation band in the ultraviolet region,while the Mo6+ ions replacing the W6+ ions at position B2 cause cleavage of energy level and reduce luminous intensity due to the change of spinorbit coupling.The internal quantum yield of BaLaLi0.4Na0.6WO6:Eu3+red phosphor obtained by cation substitution can reach 49.6%under near-ultraviolet excitation.The white LED device obtained by combination with commercial phosphor and the near-ultraviolet chip has 83.3 color rendering index and 4437 K correlated color temperature,which proves that the phosphor has application potential in the field of white light illumination excited by ultraviolet or nearultraviolet regions.(3)A series of A-position substituted red phosphors Ba1-xSrxLaLiWO6:0.10Eu3+were designed and synthesized.The substitution of Sr2+ ions to the A position significantly enhanced its luminous intensity.The enhancement mechanism was determined to be the substitution of the A position reducing the local symmetry and causing the increase of the supersensitivity transition intensity of Eu3+ions.The internal quantum efficiency of the red phosphor obtained by Aposition substitution can reach 95.3%,and it still has a luminous intensity of 80.6%at room temperature at 200℃.It also has extremely standard red emission color coordinates(0.667,0.332)and a color purity of 94.79%.The excellent comprehensive performance makes it have ideal practical value and obtains a relatively successful practical experience in linking crystal structure and luminescence performance. |
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