Preparation, Fabrication And Luminescent Properties Of Phosphate Luminescent Materials For White Light-emitting Diodes

Recently,rare earth luminescent materials play a more and more important role in lighting and display.The development of high-performance rare earth luminescent materials not only relates to the lighting needs of each household,but also to the national important layout of lighting and display industries.As the fourth generation of light source,white-LED has many advantages such as good energy saving,long lifetime,high luminescence efficiency,safety and environmental protection.As one of the key technologies for white-LED,the research of phosphors material has an irreplaceable position.Due to the defects of low white color rendering index and high color temperature,the currently commercialized way to produce white light by blue LED chip and yellow phosphor(YGA:Ce³⁺)cannot break through the bottleneck.Therefore,the development of a single-substrate phosphor for white-LED is of great importance.In the first part,a series of reddish orange light-emitting NaBaLa₂?PO₄?₃:Sm³⁺(NBLP:Sm³⁺)phosphors are designed and synthesized for the first time by high-temperature solid-state method.The crystal structure of NaBaLa₂?PO₄?₃?NBLP?has been studied by the Rietveld refinement analysis,which shows that the NBLP belongs to eulytite-type orthophosphate.Luminescence properties of NBLP:Sm³⁺phosphors were investigated in detail,including excitation and emission spectra,concentration quenching,fluorescence decay,Inokuti-Hirayama?I-H?model analysis,etc.The Commission Internationale de L'Eclairage?CIE?coordinates exhibited a shift slightly from reddish-orange?0.5782,0.4171?to orange?0.5605,0.4312?with the increase of Sm3t concentration.In addition,the NBLP:Sm³⁺phosphor shows good thermal stability and acceptable quantum efficiency.In the second part,a series of novel red-emitting Ca₈ZnLa_1-xEu_x?PO₄?₇ phosphors were successfully synthesized using the high-temperature solid-state reaction method.All the phosphors belong to whitlockite-type?-Ca₃?PO₄?₂ structures.These phosphors show no quenching,and exhibited good color coordinates?0.6516,0.3480?,high color purity?⁹6.3%?,and high quantum efficiency?⁷8%?and possess good thermal stability.A white light-emitting diode?LED?device were fabricated by integrating a mixture of obtained phosphors,commercial green-emitting and blue-emitting phosphors into a near-ultraviolet LED chip.The fabricated white LED device emits glaring white light with high color rendering index?83.9?and proper correlated color temperature?5570 K?.In the third part,a series of Tb³⁺and Tb³⁺/Eu³⁺doped Ca₈ZnLa?PO₄?₇?CZLPO?phosphors have been synthesized using a high-temperature solid-state method.Under 366nm excitation,the CZLPO:Tb³⁺,Eu³⁺phosphors exhibit a tunable multi-color emission owing to energy transfer from Tb³⁺to Eu³⁺via a quadrupole-quadrupole interaction mechanism.The fluorescence intensity ratio(I₅₄₂ nm/I₆₁₁ nm)for the Tb³⁺/Eu³⁺of this material displayed excellent temperature sensing properties between 298 and 498 K.Finally,a series of CZLPO:0.01Tm³⁺,xDy³⁺and Ca₈ZnLa?PO₄?₇:0.1Dy³⁺phosphors were prepared by high-temperature solid-state method.Through the investigation of PL-PLE fluorescence spectrum and fluorescence decay curve,CZLPO:0.01Tm³⁺,xDy³⁺phosphors can be adjusted from blue to yellow,and could be achieved white-light emission from a single host with good thermal stability.In the CZLPO,the energy transfer process of Tm³⁺?Dy³⁺is electric dipole-electric quadrupole interaction,which is explored in detail according to Dexter's energy transfer theory and Reisfeld formula.