Preparation Of Garnet Structure Green Phosphor By Molten Salt Method And Research On Its Luminescence Properties

White LED,with the advantages of high luminous efficiency,fast response,long service life and green environmental protection,is considered to be the fourth generation of illumination source.Replacing YAG:Ce3+ yellow phosphors with green and red phosphors combined with blue LEDs to form white LEDs can improve color rendering index and lower color temperature.Among the green phosphors for white LEDs,the garnet-structured LuAG:Ce3+ phosphor has the advantages of good thermal stability,high quantum efficiency,and strong blue Eght absorption.The preparation of LuAG:Ce3+ phosphors is usually carried out by a high-temperature solid-phase method,which has the disadvantages of high sintering temperature,uncontrollable microscopic morphology,and large and uneven particle size of the sample particles.In contrast,the molten salt method can effectively overcome the shortcomings of the high temperature solid phase method,reduce the synthesis temperature,shorten the sintering time,and improve the sample morphology.Based on this,a series of LCAG:Ce3+ green phosphors,BaLu2Al4SiO12:Ce3+ and MxBa1-xLui.94Al4SiO12:Ce3+(M=Sr,Ca)phosphors with the same garnet structure were prepared by molten salt method.And the structure,morphology,and luminescence properties were studied.The main research work results are as follows:(1)Lu3-xCexAl5O12(x = 0.03?0.15)series green phosphors were successfully prepared by using mixed molten salt composed of NaNO3?KNO3 and Na2CO3.The LuAG:Ce3+ phosphor was prepared by the molten salt method.The synthesis temperature was 1500 ?,which was about 300 ? lower than that of the high temperature solid phase method.The synthesized sample particles had good dispersibility,smooth surface,fine particle size and the diameter of average particle size is approximately 0.54 ?m.The optimal Ce3+ doping concentration was determined to be x=0.12.When the doping concentration was higher than the critical concentration,a significant concentration quenching phenomenon occurred due to the interaction of the electric dipole-electric dipole.The color of the phosphor can be adjusted by adjusting the Ce3+ doping concentration.As the Ce3+ concentration increases,the Lu3-xCexAl5O12(x = 0.03?0.15)phosphor has a luminescent color that changes from light green to yellow-green.(2)A series of BaLu2-xAl4SiO12:Ce3+x(0.02?x?0.08)phosphors were successfully prepared by one-step sintering with using NaF and KF as molten salts.The performance optimization experiments were carried out by adjusting the amount of molten salt,calcination temperature and holding time.The optimum amount of molten salt,sintering temperature and holding time were determined to be R=1.0,1200? and 6 h,respectively.Pure target products can be prepared under different molten salt dosages,and the particle size of the sample particles increases with the increase of the amount of molten salt.However,when the amount of the molten salt is too large,the particles will grow abnormally,the morphology of the sample becomes irregular,the particle size distribution is uneven,and the luminous intensity is also lowered.In addition,as the sintering temperature increases and the holding time increases,the particle size of the particles increases,and the impurity phase gradually disappears.However,when the sintering temperature is further increased or the holding time is prolonged,the volatilization of the molten salt is accelerated,resulting in agglomeration of the sample particles and a decrease in luminescent properties.(3)The matrix cation Ba2+ was replaced by the alkaline earth metal cation Sr2+ or Ca2+.The MxBa1-xLu1.94Al4SiO12:Ce3+0.06(M=Sr,Ca)green phosphor was successfully prepared by one-step sintering by molten salt method.As the doping amount of Sr2+ or Ca2+ increases,the unit cell shrinks,and the luminescence intensity of the sample increases first and then decreases.When the doping amount of Sr2+ or Ca2+ is x=0.05 and x=0.10,respectively,the maximum value is reached.For the M=Sr sample,the emission peak wavelength was red-shifted from 507 nm to 516 nm under the combined action of crystal field splitting enhancement and Stokes shift.For the sample with M=Ca,the red shift effect caused by the crystal field splitting is stronger than the blue shift effect caused by the Stokes reduction,and finally the emission peak wavelength is red shifted from 509 nm to 514.2 nm.When the temperature reached 200 ?,the luminescence intensity of the samples of Sr= 0.05 and Ca = 0.10 was maintained at 77%and 74%at room temperature,respectively,showing good thermal stability.