Luminescence Enhancement And Particles Size-reduction Of YAG:Ce³⁺ Phosphor

Ce³⁺doped yttrium aluminum garnet phosphor(YAG:Ce³⁺)can emit bright yellow light under blue light excitation and it is a mature commercial luminescent material.White light-emitting diodes?w LED?devices fabricated by YAG:Ce³⁺phosphor and In Ga N chips are widely used in lighting and display fields due to its advantages of energy saving,high light efficiency and long lifetime.The luminescence performance of YAG:Ce³⁺phosphor directly determines the optical properties of w LED such as the brightness,color temperature and color coordinates.Therefore,further improving the performance of YAG:Ce³⁺phosphors on the existing basis can effectively improve the light efficiency of w LED.In addition,particle size and size distribution also have an important effect on the application of phosphors.As the size of the LED chip in Micro-LED,which is the new-generation display technology,has been reduced to less than 50?m,the size of the phosphor must also be reduced accordingly to match it.But the particle size of the phosphor prepared by the traditional high-temperature solid state method is above 10?m,which cannot meet the requirements of Micro-LED technology.Therefore,a new method to reducing the particle size of YAG:Ce³⁺phosphor is highly needed in the development of Micro-LED technology.Moreover,even in ordinary w LED,phosphors with small particle diameters and narrow distributions can obtain better optical properties after packages.In order to improve the luminescence performance of YAG:Ce³⁺phosphor and expand its application field to Micro-LED,this study has conducted two explorations.The first is the optimization and improvement of the luminescence performance of YAG:Ce³⁺,and the second is the particle size-reduction of YAG:Ce³⁺phosphor powder.Graphite-like carbon nitride?g-C₃N₄?is a new type of polymer semiconductor material.g-C₃N₄ can be used as luminescent and photocatalytic material because of its advantages of visible light response,simple preparation method,low cost of raw materials,and controllable electronic properties.The band gap of graphite phase carbon nitride is about 2.7 e V,and it can emit 460 nm blue light,which is consistent with the excitation wavelength of YAG:Ce³⁺?about 460 nm?.In this research,g-C₃N₄was used to coating YAG:Ce³⁺powders to optimize and improve the luminescence performance of the phosphor.A YAG:Ce³⁺@C₃N₄ luminescent material with core-shell structure was prepared.The effect of g-C₃N₄ coating on the luminescence performance of YAG:Ce³⁺phosphor was studied,and the crystal structure,surface morphology and element distribution of the sample were analyzed.The results show that g-C₃N₄ can be successfully coated on the surface of the YAG:Ce³⁺phosphor by solution method.After the coating,a synergistic effect between g-C₃N₄ and YAG:Ce³⁺is beneficial to the luminescence performance of YAG:Ce³⁺.Further heat treatment of the coated sample can eliminate defects and improve the crystallinity of the coating layer.Ultimately,the emission intensity of g-C₃N₄ coated and heat treated YAG:Ce³⁺phosphor is 26%higher than original YAG:Ce³⁺.There is no significant change on the crystal lattice of YAG after coating and heat treatment.Furthermore,the thermal stability of the coated phosphor has also been improved due to the coating layer prevent Ce³⁺from oxidation.Size reduction of YAG:Ce³⁺phosphor particles is achieved via a two-step method of carbon coating and heat treatment.Using acetylene as the carbon source,chemical vapor deposition?CVD?was applied to coat the YAG:Ce³⁺phosphor with carbon,followed by heat treatment to remove the carbon layer.In the heat treatment process,carbon reacts with oxygen ions in the phosphor to form CO or CO₂.The reaction results in the phosphor particles breaking into smaller particles.The particle size characterization indicates that the median particle size?D50?of the phosphor has decreased from 19.1?m to 1.44?m.However,the size-reduced phosphor particles show a certain agglomeration,and heating with nitric acid can significantly improve the agglomeration.After the acid washing,the median particle diameter of the phosphor was further reduced to 0.96?m.It is demonstrated that phosphor particle size has been successfully reduced yet the photoluminescent properties still maintain the same.The carbon coating and further heat treatment method shows potential application in size control of YAG:Ce³⁺phosphors,and it is expected to be used in Micro-LED display technology.