Synthesis And Properties Of Ternary-Aluminum-Garnet Phosphors For White LEDs

In recent years,white LEDs have been widely used in many fields,such as lighting,vehicles,backlights and decorations,because of its energy saving,fast response and long lifetime.So far,the combination of a blue LED chip and yellow phosphors has been the main route to generate white light.Because of the deficit of the red component in the emission spectrum,YAG: Ce³⁺ can not meet the needs of high color rendering for lighting.By contrast,as an alternative yellow phosphor,TAG: Ce³⁺ has a high color rendering index for white LEDs,however,it has a poor thermostability which could badly impact on the use of white LEDs.Therefore,it has a high practical value and broad application prospect to improve the thermal stability and keep high color rendering index at the same time.In this thesis,we focus on the doping of rare earth ions in the aluminum garnet phosphors.The compositional ratios of Y/Tb/Lu have been designed by the triangle coordinate system,and solid solution phosphors were prepared by solid-state reaction method.The effect of compositional ratios on crystalline structure,morphology,photoluminescence properties and thermal stability was investigated by X-ray diffractometer,scanning electron micrograph,and fluorescence spectrophotometer,respectively.In addition,the optical properties of white LEDs were measured by electronic optical measurement system.The main results are as follows:?1?(Tb_xLu_1-x)2.9Al₅O₁₂: Ce³⁺,?Tb_xY1-x?2.9Al₅O₁₂: Ce³⁺,and?Lux Y1-x?2.9Al₅O₁₂: Ce³⁺phosphors have been prepared.It is found that the binary solid solution will form after doping Tb³⁺ or Lu³⁺ into the matrix,and the substitution will not alter garnet structure.With the doping of Tb³⁺,the emission spectrum of Lu AG: Ce³⁺ shifts from 507 nm to 544 nm,and the emission intensity reduces.When Tb³⁺ions were doped into YAG: Ce³⁺,the emission spectrum shifts from 533 nm to 544 nm.When the concentration of Tb³⁺ is 40mol%,the intensity rises up to the maximum.Instead,the emission spectrum of YAG: Ce³⁺shifts to shorter wavelength?from 532 nm to 506 nm?by doping Lu³⁺,and the intensity reaches the maximum when the doping concentration is 80 mol %.?2?(Y_xTb_xLu_1-2x)2.9Al₅O₁₂: Ce³⁺,?Y_xTb1-2x Lux?2.9Al₅O₁₂: Ce³⁺,?Y1-2x Tb_xLux?2.9Al₅O₁₂:Ce³⁺,?Y1/3Tb_xLu2/3-x?2.9Al₅O₁₂: Ce³⁺,?Y_xTb2/3-x Lu1/3?)2.9Al₅O₁₂: Ce³⁺and?Y_xTb1/3Lu2/3-x?2.9Al₅O₁₂: Ce³⁺ phosphors have been prepared.It is found that matrix ions can be substituted by doping of rare earth ions,and will form ternary solid solution.When doping with Y³⁺/Tb³⁺,the emission spectrum of Lu AG: Ce³⁺shows a redshift from 506 nm to 540 nm,and the intensity decreases by 80%.The emission spectrum of TAG: Ce³⁺ has a blue shift?from 544 nm to 537 nm?,and the intensity increases.With the doping of Tb³⁺/Lu³⁺ions,the emission wavelength of YAG: Ce³⁺shifts from 532 nm to 537 nm,but the emisssion intensity shows a trend which decreases first and then increases.The doping of Tb³⁺ can make the emission bands of?Y1/3Lu2/3?2.9Al₅O₁₂:Ce³⁺ phosphors shift from 528 nm to 543 nm,and the intensity decreases.With the doping of Y³⁺ions,the emission spectrum of?Tb2/3Lu1/3?2.9Al₅O₁₂:Ce³⁺ shows a blueshift?from 543 nm to 517 nm?,and the emission enhances.Conversely,as?Tb1/3Lu2/3?2.9Al₅O₁₂:Ce³⁺ phosphors were doped with the same Y³⁺ions,the wavelength shifts from 535 nm to 541 nm,and the intensity decreases.?3?A series of(Y_xTb_yLu_1-x-y)2.9Al₅O₁₂: Ce³⁺ phosphors have been synthesized,and the three-dimensional spectrum have been established.It is found that the emission wavelength and intensity can be controlled in a triangle area through adjusting the compositional ratio of Y/Tb/Lu.Moreover,the thermostability of aluminum garnet phosphors has been investigated,and the results show that the Y³⁺/Lu³⁺co-doped can effectively improve the thermostability.Besides,when Y³⁺/Tb³⁺/Lu³⁺ is 1/6:1/3:1/2,the thermostability of(Y_1/6Tb_1/3Lu_1/2)2.9Al₅O₁₂:Ce³⁺ phosphors has improved by 7 % compared to TAG: Ce³⁺,and the emission spectrum shifts by 4 nm compared to YAG: Ce³⁺.The white LED coupled 450 nm blue chips with(Y_1/6Tb_1/3Lu_1/2)2.9Al₅O₁₂:Ce³⁺ phosphor shows?0.3283,0.3250?of chromaticity coordinate,77.5 of Ra(YAG: Ce³⁺ is 72.9),and it is a promising yellow emitting phosphor for fabrication of white LEDs.