Study On The Preparation And The Luminescent Properties Of Aluminate Based Phosphors For White LED

White light emitting diode?WLED?has great application prospect in the field of display and lighting owing to its excellent performance such as high efficiency,low energy consumption,long life and environmental friendly,.Aluminate based phosphors for white LED,which possess high quantum efficiency,good color,wide excitation spectra,emission light in visible range,high brightness,chemical stability and low price,have become a hot research topic of fluorescent material.Therefore,the research and development of various types of aluminate based phosphor for white LED is particularly important.In this article,high temperature solid state method and sol-gel method were used to synthesize the aluminate based phosphors,and the luminescence properties of the synthesized phosphors were discussed.In the first chapter,there was a brief introduction of the application of white LED,luminescent materials and mechanism,and the research on all kinds of aluminate based phosphors.The second chapter presents the experimental methods and characterization methods.And from the third chapter to the sixth chapter,the luminescent properties of Ca₁₂Al₁₄O₃₂F₂,CaYAlO₄and LaAlO₃based phosphors were studied.In the third chapter,a series of Ca₁₂Al₁₄O₃₂F₂:Eu phosphors were synthesized by high temperature solid state method,in which the row materials were calcined at1250?for 4 h under the reduction atmosphere of N₂:H₂=9:1.By changing the substrate composition,such as substitution of O^2-by halogen?F^-,Cl^-?,Ca²⁺by alkaline earth metal ions(Mg²⁺,Sr²⁺,Ba²⁺),and Al³⁺ions in AlO₄^-by B³⁺,Si⁴⁺and Ge⁴⁺,the coexistence of Eu²⁺-Eu³⁺ions in Ca₁₂Al₁₄O₃₂F₂:Eu were studied.XPS data show that the synthesized samples Ca₁₂Al₁₄O₃₂F₂:Eu contain Ca,Al,O,F,Eu five elements.The samples launch blue light?400-550 nm?of Eu²⁺and red emission?580-720 nm?of Eu³⁺under ultraviolet light excitation between 220-300 nm,respectively.Upon excitation between 300-400 nm,the samples onlyemit blue light?400-550 nm?of Eu²⁺.When the doping amount of F^-or Cl^-ion is 0.5,the intensity ratio of the blue and red light(I_blue/I_red)reach the maximum.When a small amount of Mg²⁺ions was doped inthe sample,the Eu²⁺was not conducived to generate because of the radius of Mg²⁺ion is less than than of Eu²⁺.A small amount doping of Sr²⁺and Ba²⁺ions,the Eu²⁺was conducived to appear by doping some Sr²⁺or Ba²⁺ions because of their radius were similar to Eu²⁺.With the concerntration of Ba²⁺increasing,the emission red shift appear because the ionic radius of Ba²⁺was too large to lead to serious lattice distortion and impurity phase.It had impact on the coexistence of Eu³⁺and Eu²⁺ions by doping B³⁺,Si⁴⁺or Ge⁴⁺in matrix.It was conducived to form Eu²⁺ions by doping some concentration of Si⁴⁺or Ge⁴⁺.SEM images showed that the particles of the sample was not uniform,and had irregular shape and the obvious phenomenon of reunion.In the fourth chapter,a series of single doped CaYAlO₄:R(R=Eu³⁺,Mn⁴⁺,Tb³⁺,Dy³⁺,Ho³⁺,Sm³⁺,Tm³⁺)phosphors were synthesized by sol-gel method in air atmosphere,the synthesis condition and the luminescent properties of CaYAlO₄:R phosphors with different doping ions was studied.The TGA and DSC curves of dry glue show an obvious exothermic peak at 1200?,and the pure sample with tetragonal structure was obtained bycalcining between 1100?¹350?for 6 h.Under the excitation of UV light,the synthesized samples exhibit feature transitions of the doping ions,emit their unique lights,respectively.The luminescent intensity of CaYAlO₄:R sample reaches a miximum when the concentration of Eu³⁺,Mn⁴⁺,Tb³⁺,Dy³⁺,Ho³⁺,Sm³⁺and Tm³⁺is 2%,0.5%,1%,3%,1.5%,1.5%and 2%,respectively.The mechanism of fluorescence quenching for Eu³⁺,Ho³⁺or Sm³⁺is the interaction between neighboring ions,and that for Mn⁴⁺or Tb³⁺is dipole-dipole interaction,and for Dy³⁺is dipole-quadrupole interaction.TEM images display that the morpholoties arecomposed of irregular shape,uneven size and serious particle agglomeration.The particles have a size ranged from 1 nm to 100 nm.In the fifth chapter,a series of co-doped CaYAlO₄:R(R=Ce³⁺,Tb³⁺,Eu³⁺)phosphors were synthesized by sol-gel method in reduction atmosphere of N₂:H₂=9:1 and calcining at 1300?for 6 h.The fluorescence properties of codoped ions of Ce³⁺-Eu³⁺,Ce³⁺-Tb³⁺,Tb³⁺-Eu³⁺,and Ce³⁺-Tb³⁺-Eu³⁺were studied.The results show that the energy transfer between Ce³⁺and Tb³⁺ions exist,the energy of Ce³⁺could be efficiently transferred to Tb³⁺.The energy transfer between Ce³⁺and Tb³⁺or Tb³⁺and Eu³⁺is not obvious,The emissions could be changed from blue to green for co-doped Ce³⁺-Tb³⁺,from blue to orange red for Ce³⁺-Eu³⁺,and from green to orange red for Tb³⁺-Eu³⁺.And the emissions of Ce³⁺-Tb³⁺-Eu³⁺vary from blue to green,and then to orange red.Near white light can be obtained by adjusting the concentration of Ce³⁺,Tb³⁺and Eu³⁺.In the sixth chapter,a series of LaAlO₃:R(R=Eu³⁺,Mn⁴⁺,Tb³⁺,Dy³⁺,Sm³⁺,Tm³⁺)phosphors were synthesized in air atmosphere by sol-gel method.The synthesis conditions and the luminescent properties of different doping ions were studied.The TGA and DSC curves of dry glue show an obvious exothermic peak at 860?,and the pure sample with trigonal crystal structure was obtained by calcining between800?¹200?for 4 h.Under the excitation of UV light,the synthesized samples exhibit feature transitions of the doping ions,emit their unique lights,respectively.The luminescent intensity can be changed by changing the doping concentration.