Synthesis And Spectroscopic Properties Of RE³⁺(Nd³⁺,Ce³⁺):YAG Ultra-fine Powders

YAG (yttrium aluminium garnet) is an excellent host for laser and luminescent materials. Nd-doped yttrium alumlnium garnet (Nd:YAG) is an important solid-state laser host, and has been widely used in various areas. Recently high transparent Nd:YAG ceramic laser materials have drawn great attention because of its advantages in short cycle of fabrication and high doping concentration. Ce3+-doped yttrium aluminium garnet (YAG:Ce3+) phosphor is the key to commercial white LED.It is fabricated by coating YAG:Ce3+ phosphors on the chip of blue LED. YAG:Ce phosphors emit yellow light excited by the blue light and the two waves of lights mixed into white light.Urgent needs of ultra-fine powders are made by laser materials and white LED light conversion materials,synthesis of powders has become a key technology. Therefore, research on Nd: YAG and YAG:Ce3+ powders has important practical significance.In this dissertation, the chemical co-precipitation and low temperature combustion methods are employed to synthesize Nd:YAG nano-sized powders, the effects of the precipitants, solution concentration, pH value, manner of titrating, heat treatment to the phase formation and spectroscopic properties are studied. Meanwhile sol-gel and homogenous precipitation method are employed to prepare YAG:Ce3+ phosphors, and the amount of citric acid, pH value,concentration of Ce3+, sintering temperatures to the phase formation and spectroscopic properties are also studied. The structure and properties of samples are characterized by IR, TG-DTA, XRD,SEM,TEM and PL analysis methods.(1) (NH4)2CO3 and NH4HCO3 are employed as precipitants to prepare Nd:YAG powders. The precursor can transform into pure YAG phase at 900℃,when the molar rate of (NH4)2CO3 and metal ion is 7, dropping rate is less than 2ml/min.The adding of polyethylene glycol can improve the dispersion of the powders. The spherical particles are distributed uniformly with diameters of 50nm～100nm.The precursor can transform into pure YAG phase at 1000℃, when the molar rate of NH4HCO3 and metal ion is 10, dropping rate is less than 2ml/min.The adding of polyethylene glycol can improve the dispersion of the powders, The particles are distributed uniformly with diameters of 80nm-120nm.(2) Citric acid is employed as burning agent to prepare Nd:YAG powders by low temperature combustion method. The precursor can transform into pure YAG phase at 1100℃. With the extended holding time, the lattice parameters decrease.The adding of glycol can improve the dispersion of the powders, the spherical particles distributed uniformly with diameter of 100nm.There are three characteristic emission peaks of Nd: YAG nano-sized powders, which locates at 946nn,1065nm and 1340nm respectively, corresponding to the transitions of 4F3/2→4I9/2,4F3/2→4I11/2 and 4F3/2→4I13/2.The most intense emission peak locates at 1065nm.(3) YAG:Ce3+ phosphors are also prepared by citrate acid sol-gel method. The particles sintered at 1100℃for 3 hours are spherical in shape with uniform particle size of 90nm～110nm. The excitation spectra of YAG:Ce3+ phosphors are broad band with two prominent peaks located at 340nm and 460nm respectively, corresponding to the transition of 2F5/2→5d and 2F7/2→5d of Ce ions. The emission spectra of YAG:Ce3+ phosphor are also broad band with the maximum emission peak located at 530nm. Emission intensity increases as temperatures increase.When molar fraction x of Ce3+ ion dopant is 0.07, emission peak intensity of phosphors reach its maximum.(4) YAG:Ce3+,Gd3+/Sm3+ phosphors are synthesized by malonic acid sol-gel method.The results indicate that the phosphors can be obtained at 1200℃, the particle size is about 0.3～1μm with a ball morphology.Experimental results showed that Gd3+ ion dopant doesn't affect excitation peak wavelength in excitation spectra of phosphors.The emission spectrum of phosphor gradually red-shift from 525nm to 550nm with the increase of the concentration of Gd3+ ion.Two peaks exist for the emission spectra,which located at 540nm and 617nm with the doping of Sm3+,increasing the red component and color rendition of YAG:Ce3+ phosphor.(5) Homogeneous precipitation method is firstly used to prepare YAG:Ce3+ phosphors. The precursor can transform into YAG:Ce3+ phosphors at 1200℃.The spherical particle size is about 100nm.The adding of (NH4)2SO4 and polyethylene glycol improve the dispersion of the powders. Excitation peaks of phosphors locates at 341nm and 467nm,the maximum emission peak of YAG:Ce phosphor locates at 528nm.