Preparation And Luminescence Properties Of Y_3-x?Lu_x?Al₅O₁₂:Ce³⁺ Phosphors By Molten Salt Synthesis Mehtod

The luminescent materials of yttrium aluminum garnet?YAG?doped with rare earths are widely used in different areas,such as illumination light sources,displays,lasers,etc.The traditional synthetic method,high temperature solid phase method,has the disadvantages of high synthesis temperature,long reaction time,and needs to be ground to obtain the required size.In contrast,the molten salt synthesis?MSS?method shows significant advantages because of the characteristics of low energy consumption,easy operation and little pollution.White light can be obtained by combining Y_3-x-x Al₅O₁₂:Ce_x³⁺(YAG:Ce³⁺)yellow phosphor with blue LED chip.However,the white LED has poor color rendering due to lack of red light and green light.Meanwhile,the phosphor is prone to temperature quenching when the temperature rises.In this work,the optimum experimental conditions for synthesing YAG:Ce³⁺phosphors by MSS method with different inorganic salts as molten salts were systematically studied,and the molten salt combination most beneficial to phosphorescence was selected.Lu³⁺ions were introduced into YAG host to adjust the spectral range,increase the emission band in the green region,broaden the emission spectral range,and increase the thermal stability of the phosphor;the red emissions were supplemented by co-doping Ce³⁺-Pr³⁺or Ce³⁺-Sm³⁺in Y_3-xLu_xAl₅O₁₂?YLuAG?to improve the luminescence performance of the white LED and enhance the color rendering of the white LED.YAG:Ce³⁺?YLuAG:Ce³⁺?YLuAG:Ce³⁺,Pr³⁺and YLuAG:Ce³⁺,Sm³⁺phosphors were prepared by the MSS method.The main research is as follows:?1?The optimum experimental conditions for preparing phosphors with different binary composite salts as molten salts were studied through the orthogonal experimental method and the luminescence intensity was used as the evaluation index.The experimental conditions included reaction temperature,sintering time and salt-to-reactant molar ratio.Comparing the luminescence properties and the particle morphology of the samples obtained from the ternary composite salt and the binary composite salt,it was determined that the phosphor using 0.8NaF-0.1NaCl-0.1KCl as the molten salt had the highest luminous intensity,and the particle morphology was nearly spherical and uniform in size.The best experimental conditions are salt-to-reactant molar ratio of 2:1 at 1 350°C for 2 hours.?2?The effects of introducing Lu³⁺ions into YAG:Ce³⁺phosphors on the lattice phase,luminescence properties,surface morphology and luminescence thermal stability were investigated.It was found that Lu can enter the crystal lattice and replace the position of Y in YAG.When Y³⁺ions were completely replaced by Lu³⁺ions,Lu_3-xAl₅O₁₂:Ce_x³⁺(LuAG:Ce³⁺)phosphor with the same garnet structure was obtained.Increasing the concentration of Lu³⁺,the emission peak of YLuAG:Ce³⁺was blue-shifted,and the temperature reliability was improved.When the concentrarion of Lu³⁺was less than 1.5,the particle morphology was more stereoscopic with the increase of Lu³⁺.After the concentration of Lu³⁺exceeded 1.5,the morphology of the particles was irregular and the lattice is distorted.When Lu³⁺completely replaced Y³⁺to form LuAG,the particles returned to a uniform cubic structure.The Ce³⁺dopant which is favorable for YLuAG:Ce³⁺phosphor luminescence intensity was determined.?3?Pr³⁺or Sm³⁺was doped into the YLuAG:Ce³⁺phosphor to increase the red emission of the phosphor.The luminescent properties of YLuAG:Ce³⁺,Pr³⁺and YLuAG:Ce³⁺,Sm³⁺ were tested,and the optimum dopants of Pr³⁺and Sm³⁺were determined.The energy transfer between Ce³⁺-Pr³⁺or Ce³⁺-Sm³⁺was studied,respectively.The photoelectric properties of white-LED encapsulated by YLuAG:Ce³⁺,Pr³⁺and YLuAG:Ce³⁺,Sm³⁺ phosphors with blue chip were tested.It was found that the Pr³⁺ions-doped or Sm³⁺ ions-doped phosphor helped to obtain high color rendering and high efficacy white-LED,and it was more conducive to obtaining white-LEDs with high color rendering and high luminous efficiency.