Preparation And Properties Of Rare-earth Ce³⁺/Tb³⁺ Doped Inorganic Luminescence Materials For Warm White LED

In recent years,rare-earth doped luminescent materials have gained much attention and deep research due to its bright application prospects.Due to the merits of small size,long working time,and environment friendly,light-emitting diodes(LED)as the rare-earth doped luminescent materials play important role in lighting field.LED chip can convert electrical energy into light energy,and emit monochromatic light.Phosphor-converted white LED mainly consists of two important parts:(1)ultraviolet/near ultraviolet(n-UV;350-420 nm)/blue chip;(2)phosphors with specific emission wavelength.The method of fabricated white LED using yellow-emitting YAG:Ce³⁺phosphors with blue LED chip has been commercialized.However,due to the lack of red phosphors/spectral composition,the white light exhibits high correlated color temperature(CCT>4500 K)and low color rending index(Ra<80).Thus,the white light obtained by this method is usually cold white light,which seriously affected its wide application in the field of lighting.Another alternative method is using UV/n-UV chip with trichromatic RGB phosphors(R:red;G:green;B:blue)to generate white light.This method has the advantage of spectral tunability and its spectral covering red,green,and blue composition.Thus,red,blue,and green phosphors with excellent optical properties have received extensive attention and profound research.However,this white light obtained by the alternative method have a spectral defect(trough)in the cyan region(480-520 nm wavelength range),which makes it have a low Ra.Therefore,in order to improve the Ra of the white LED device,the cyan-emitting phosphors are particularly important.In this paper,we mainly study the Ce³⁺and Ce³⁺-Tb³⁺co-doped phosphors,which have great application potential,and the corresponding crystal structure,luminescence spectra(optimal doping concentration,excitation and emission spectra,color coordinates,and thermal stability),and device application were analyzed in detail.(1)Blue-green light adjustable phosphors were synthesized by solid state reaction.Excited by 345 nm,Ca₃Lu(Ga O)₃(BO₃)₄:Ce³⁺could emit the blue light in the 350-550 nm wavelength range with optimal emission peak of 400 nm.It need to be noticed that the Ce³⁺-Tb³⁺co-doped Ca₃Lu(Ga O)₃(BO₃)₄:0.04Ce³⁺,y Tb³⁺phosphors can show not only Ce³⁺but also Tb³⁺ions characteristic emission peaks.Due to the energy transfer from Ce³⁺to Tb³⁺ions,Ca₃Lu(Ga O)₃(BO₃)₄:0.04Ce³⁺,y Tb³⁺phosphors can realize the spectral adjusting from the blue region(y=0.00;CIE:(0.164,0.042))to green region(y=0.50;CIE:(0.331,0.485)).The optimal Ca₃Lu(Ga O)₃(BO₃)₄:0.04Ce³⁺,0.40Tb³⁺phosphors have the IQE of 54.2%,and its emission intensity at 423 K still remain 74%of that at 303 K.Based on the Ca₃Lu(Ga O)₃(BO₃)₄:0.04 Ce³⁺,0.40Tb³⁺phosphors,we fabricated a white LED device excited by a 365 nm chip.The obtained white light have a high Ra of 81.2 and low CCT of 3588 K,indicating the Ca₃Lu(Ga O)₃(BO₃)₄:0.04Ce³⁺,0.40Tb³⁺phosphors have a great application prospect in the warm white LED field.(2)The synthesis method of the Ca₂YZr₂(Al O₄)₃:Ce³⁺,Tb³⁺phosphors was high temperature solid-state reaction method.The Tb³⁺singly-doped Ca₂YZr₂(Al O₄)₃:Tb³⁺phosphors cannot be excite by 408 nm,but the Ce³⁺singly-doped Ca₂YZr₂(Al O₄)₃:Tb³⁺phosphors can efficiently excited by the 408nm.Due to the existence of the energy transfer from Ce³⁺to Tb³⁺ions,the Ce³⁺-Tb³⁺co-doped Ca₂YZr₂(Al O₄)₃:0.04Ce³⁺,0.9Tb³⁺phosphors showed two broad excited band in the 300-470 nm wavelength range with the optimal excitation peak of 408 nm.Under the excitation of 408 nm,Ca₂YZr₂(Al O₄)₃:0.04Ce³⁺,0.9Tb³⁺phosphors exhibited bright green emission due to ⁵D₄?⁷F_J(J=6,5,4,3)transition of Tb³⁺ions,which is similar with the emission band of the Tb³⁺singly-doped Ca₂YZr₂(Al O₄)₃:Tb³⁺phosphors.The full width at half-maximum of the 543 nm emission peak of the Ca₂YZr₂(Al O₄)₃:0.04Ce³⁺,0.9Tb³⁺phosphors was 13.5 nm,and the internal quantum efficiency of the Ca₂YZr₂(Al O₄)₃:0.04Ce³⁺,0.9Tb³⁺phosphors was56%.The fabricated white LED device showed that under the 30 m A driven current,the white device could emit bright warm white light,which have high Ra of 91,CCT of 3233 K.Thus,as green-emitting phosphors,Ca₂YZr₂(Al O₄)₃:Ce³⁺,Tb³⁺phosphors have bright potential in the application of the warm white LED.(3)There exists a cyan gap in the white LED device,which device was fabricated by using UV/near-UV chip together with RGB phosphors.That is to say,the emission spectrum of the device has a deep trough in the 480-520 nm wavelength range.In this paper,the synthesized Ca₂Lu Zr₂(Al O₄)₃:Ce³⁺phosphors play a roal in filling the lack of the cyan gap of the white LED device.The optimal Ce³⁺ions doping concentration is 1%.Ca₂Lu Zr₂(Al O₄)₃:1%Ce³⁺phosphors could exhibit a broad excitation band in the 370-475 nm wavelength range with an optimal excitation peak of 408 nm.Excited by 408 nm,Ca₂Lu Zr₂(Al O₄)₃:1%Ce³⁺phosphors could emit cyan light in the 414-650 nm wavelength range with a high internal quantum efficiency of 58%.It is worth noting that it played important role in filling the cyan gap in the device which was fabricated by using UV/near-UV chip and RGB phosphors.From the fabricated warm white device,we could know that the existence of the Ca₂Lu Zr₂(Al O₄)₃:1%Ce³⁺phosphors made Ra of the device increase from 82.3to 89.2.Thus,Ca₂Lu Zr₂(Al O₄)₃:Ce³⁺cyan-emitting phosphors have great application potential in the warm white LED.(4)Ca₂Lu Zr₂(Al O₄)₃:Ce³⁺,Tb³⁺phosphors were prepared by traditional solid-state reaction method.Due to the Ce³⁺optimal doping concentration was1%,we study the optical properties,energy transfer mechanism,and the white device application of the Ce³⁺-Tb³⁺co-doped Ca₂Lu Zr₂(Al O₄)₃:1%Ce³⁺,Tb³⁺phosphors fixed Ce³⁺concentration at 1%.Owing to the existence of the Ce³⁺?Tb³⁺energy transfer,the optical tunable from the cyan region to the green region was achieved.The research on the quantum efficiency showed that all as-prpared samples have internal quantum efficiency over 50%.The Ca₂Lu Zr₂(Al O₄)₃:Ce³⁺,Tb³⁺phosphors can not only showed a good thermal stability of the emission intensity,but also exhibited a good thermal stability of the CIE coordinates.Finally,we make a short summary of the research during the study period,and analysis the shortcoming needed improve of the prepared phosphors.