Preparation And Properties Of Multilayer Film With Blue Transmitted And Yellow Reflected For High-efficiency White Light LED

The white light emitting diode become the fourth-generation green lighting source because of the advantages of energy saving, environmental protection,small size, high efficiency and long life. Currently, the white LED which is realized by Ga N blue chip exciting YAG:Ce fluorescent powder has been commercialized. However, LED light extraction efficiency is influenced by the interface reflection, Fresnel effect, self absorption and other factors. Therefore,in order to improve the light extraction efficiency of white LED, multilayer film with blue transmitted and yellow reflected is designed and prepared in this artile.The results are as follows:(1) Using TFC software design the membrane system, with Zn S, Ti O2,Mg F2 were used as high, medium and low refractive index materials,respectively. The structure of the 7 layer film was obtained, and the thickness of the film is 961 nm. The transmittance reaches 98% in the range of 400-485 nm,and the reflectance is more than 99% in the range of 550-800 nm. The results meet the design requirements about blue transmitted and yellow reflected.(2) Zn S/Ti O2/Mg F2 multilayer film was deposited on glass slides by magnetron sputtering. The structure and optical properties of the multilayer film were characterized by scanning electron microscope, atomic force microscope,step instrument and UV-visible spectrophotometer. Electron microscopy analysis shows that the multilayer film has obvious interface, compact surfacestructure and the size of the membrane particles is uniform. Surface roughness RMS of 7-layer film is 6.229 nm, flatness of the film is preferable, and total film thickness is 912 nm. Transmittance spectra shows that the transmittance is about57% in the range of 430-475 nm,the reflectance is about 90% in the range of570-600 nm.(3) The YAG:Ce phosphor membrane was prepared by using OE-6550 A,OE-6550 B, YAG:Ce phosphor, tetrahydrofuran and n-hexane as raw material.Then compounded Zn S/Ti O2/Mg F2 multilayer film with YAG:Ce phosphor membrane. The optical properties of the composite film were characterized by UV-visible spectrophotometer and fluorescence spectrophotometer. UV-visible spectra shows that the pure YAG:Ce phosphor film absorbs UV light and blue light, but the absorption of the composite film in the UV region and the blue light region decreased obviously, and the composite film has no absorption peak in the yellow light region. Fluorescence spectra shows that being excited by the wavelength of 460 nm, the maximum emission peak of the pure YAG:Ce phosphor film and the composite film are located at 472 nm and 485 nm,respectively. The emission peak has red-shift and the intensity of emission peak increases, and the fluorescence intensity in the yellow light region is near 0. The results show that multilayer optical film prepared in this study play a role in blue transmitted and yellow reflected. It has potential application value in improving the light extraction efficiency of white LED.