Study On The Preparation And Luminescence Properties Of Rare Earths Fluorescent Materials For W-LEDs With N-ultraviolet Excitation

White light-emitting diodes(w-LEDs)are penetrating the lighting market at an extremely fast rate owning to their low electric consumption,environment-friendliness,high brightness,long lifetime,and fast response,etc.The commercial w-LED that consists of a blue LED chip and Y3Al5O12:Ce3+(YAG:Ce3+)yellow-emitting phosphor cannot achieve a warm white light with a low color rendering index(CRI<80)and a high correlated color temperature(CCT>4500 K).Accordingly,w-LEDs fabricated with near ultraviolet(n-UV)LED chips and tricolor(red,green and blue)phosphors are expected to dominate the market in the near future because of the better CRI value and superior color uniformity.Therefore,it is of great significance to study rare earth phosphor materials that can be applied to w-LEDs.In this paper,a series of rare earth ions doped in orthophosphate(A3Ln(PO4)3(A=Sr;Ln = Sc,Lu)were synthesized by using high-temperature solid-state reaction method.And the phase purity,crystal structure of material,fluorescent spectrophotometry,ultraviolet diffuse,thermal stability and fluorescence lifetime decay curve were systematically analyzed(1)A series of Sr3Sc(PO4)3:Dy3+ phosphors have been synthesized via a conventional high-temperature solid-state reaction method.X-ray powder diffraction(XRD),fluorescent spectrophotometry,concentration quenching mechanism and luminescence lifetime were utilized to characterize the structure and luminescence properties of the obtained phosphors.The excitation spectrum indicated that these phosphors had a strong absorption band in near-ultraviolet(n-UV)region in the range from 250 to 450 nm.There were two sharp emission peaks in the visible region,which were located at 483 nm(blue)and 576 nm(yellow)corresponding to the magnetic dipole 4F9/2?66H15/2 transition and the electric dipole 4F/9/2?6H13/2 transition of Dy3+,respectively.The commission International de I' Eclairage(CIE)of Sr3Sc0.93(PO4)3:0.07Dy3+ phosphor was calculated to be(0.28,0.32),which was very close to the "ideal white"(x = 0.33,y=0.33).The results show that Sr3Sc(PO4)3:Dy3+has a certain application prospect in the manufacture of white-light-emitting phosphor excited by n-UV.(2)A series of Sr3Lu1-x(PO4)3:xSm3+ phosphors were synthesized via a solid-state reaction method.The crystal structure of the prepared phosphors were investigated using X-ray diffraction(XRD)and Scanning electron microscopy(SEM).The excitation and emission spectra,concentration quenching mechanism,and fluorescence decays were measured and discussed systematically.Under 403 nm excitation,the 4G5/2?6HJ(J = 5/2,7/2,9/2,and 11/2)emissions of Sm3+ were obviously observed whose peaks located at 564 nm,599 nm,646 nm and 705 nm,respectively.The optimum dopant concentration of Sm3+ ions in Sr3Lu(PO4)3 is 3 mol%and the corresponding Commission International de I' Eclairage(CIE)chromaticity coordinate of the Sr3Luo.97(PO4)3:0.03Sm3+ phosphor was located in the orange reddish region.In addition,the temperature dependent luminescence of the typical sample was also investigated.The results confirmed that the as-synthesized Sr3Lu(PO4)3:Sm3+ phosphors has good luminescence performance under the excitation of n-UV.(3)A series of single-phase and color-tunable Dy3+,Eu3+ singly doped and Dy3+/Eu3+co-doped Sr3Sc(PO4)3 phosphors have been synthesized via a high-temperature solid-state reaction method.The phase purity,crystal structure and constitution of the prepared phosphors were investigated using X-ray diffraction(XRD),Scanning electron microscopy(SEM)and Energy dispersive X-ray(EDX).The excitation and emission spectra,the powder diffuse reflectance spectra(DRS)and fluorescence decays were measured and discussed.The results revealed that Dyry can efficiently transfer excitation energy to Eu3+ via its 4f states and therefore sensitized Eu3+ emission under n-UV excitation.Meanwhile,the energy transfer mechanism could be ascribed to be the dipole-dipole interaction,which can be validated via the linear fitting of the relationship(IS0/IS)? Cn/3.The Commission International de I' Eclairage(CIE)chromaticity coordinates of the phosphors can be tuned from wathet blue(0.2509,0.2149)to light orange(0.4022,0.2924)by adjusting the ratio of Dy3+ and Eu3+.(4)The novel white light emitting phosphors Sr3Lu(1-x)Dyx(PO4)3(x = 0.02,0.04,0.06,0.08,0.10)were synthesized via a conventional high-temperature solid-state reaction method at 1250?.The excitation spectrum indicated that these phosphors had a strong absorption in n-UV region in the range from 260 to 460 nm.And under 350 nm excitation,the blue emission at 483nm(4F9/2?6H15/2)and yellow emission at 576 nm(4F9/2?6H13/2)were observed in the phosphors,respectively.We studied the effect of different doping concentrations of Dy3+ activator on the luminescence properties and found that the optimum doping concentration is 6 mol%.According to the Dexter's theory,this quenching behavior is ascribed to be electric d-d interaction.The results indicate that the Sr3Lu(PO4)3:Dy3+phosphor can serve as a promising candidate for single-component white light emitting phosphor under n-UV excitation.