紫外光激发Ce^(3+)掺YVO_4蓝光发射性能研究

利用提拉法生长了YVO4和掺2.0at%CeO2(或Ce2(CO3)3)的YVO4:Ce3+晶体。样品的XRD测试表明Ce3+代替Y3+进入晶格,Ce3+的加入并没有影响YVO4的晶格结构。XPS测试显示YVO4:Ce3+晶体中Ce离子3d分裂为882.0、885.8、902.9、908.0和915.9 eV等5个峰,峰位表明样品中铈离子是以Ce3+和Ce4+两种价态形式存在。YVO4和YVO4:Ce3+激发谱都呈现出260~360 nm宽带激发,此激发带源于基质中VO43-离子团的配体O到V的电荷迁移吸收。使用325 nm的紫外线激发时,两种样品均可发出以440 nm为中心的宽带蓝光,其中YVO4发射峰应归属于VO43-离子团中3T2→1A1和3T1→1A1跃迁;而YVO4:Ce3+的蓝光发射则来源于Ce3+的5d→4f的跃迁。分析可知YVO4:Ce3+中VO43-的π轨道和Ce3+的电子波函数能有效地重叠,使得VO43-和Ce3+可通过交换作用有效地向Ce3+传递能量,可大幅提高Ce3+的蓝光发射强度。实验结果显示YVO4:Ce3+可作为UV-LED管芯激发的白光发光二极管用高亮度蓝色发光材料。

Synthesis and Luminescence Properties of Green-emitting Phosphor CaSc_(2)O_(4):Ce^(3+)

Using CaCO_(3),Sc_(2)O_(3),and CeO_(2) as raw materials,we prepared the CaSc_(2)O_(4):Ce^(3+)green phosphors for white light LEDs via a high-temperature solid-phase method in a reducing atmosphere.X-ray diffraction(XRD),field emission scanning electron microscopy(FESEM),fluorescence spectroscopy and other means were used to characterize the phase structure,apparent morphology,and photoluminescence properties of the product.CaSc_(2)O_(4) was synthesized under a reducing atmosphere(95%N_(2)+5%H_(2))at 1400℃ for 4 hours.Upon excitation with a blue light(450 nm wavelength),CaSc_(2)O_(4):Ce^(3+)displays a broadband green emission peak at 525 nm.The color coordinates of CaSc_(2)O_(4):7%Ce^(3+)emission peak are(0.3712,0.5940),and the product morphology is 1μm granular.Hence,it acts as a green phosphor suitable for white LEDs that can be excited by blue light.

Influence of Y^(3+),Bi^(3+) Content on Photoluminescence of YVO_4∶Dy^(3+) Phosphor Induced by Ultraviolet Excitation

YxVO4∶0.01Dy3+ and Y0.99-xVO4∶0.01Dy3+,xBi3+ phosphors were synthesized by chemical co-precipitation method.Their crystal structure,micromorphology and photoluminescence(PL) properties were investigated by X-ray diffraction(XRD),scan electron microscopy(SEM) and spectrofluorometer.YxVO4∶0.01Dy3+ and Y0.99-xVO4∶0.01Dy3+,xBi3+ phosphors have a broad excitation band from about 250 to 350 nm including a strongest peak at about 310 nm.Under its excitation,the emission spectra exhibits two sharp peaks,one of which centered at about 483 nm for 4F9/2→6H15/2 transition of Dy3+ and the other at about 574 nm due to the 4F9/2→6H13/2 transition of Dy3+.For YxVO4∶0.01Dy3+(x=0.94,0.97,0.99,1.01,1.03) phosphor,with increasing value of x,the body color of phosphor changes from yellow to white and the strongest peak in the excitation spectra shifts a little to shorter wavelength.It is detrimental to luminous intensity when Y3+ content deviates stoichiometric ratio.For Y0.99-xVO4∶0.01Dy3+,xBi3+(x=0.01,0.05,0.1,0.15,0.2,0.25) phosphor,the samples have extraneous bismuth vanadium oxide phase except for the major tetragonal zircon structure when x≥0.20.With increasing value of x,the band edge in the excitation spectra shifts to longer wavelength,the excitation intensity and luminous intensity increase early and decrease late.When the value of x is 0.01,the intensities increase evidently.In addition,the influence of Y3+ or Bi3+ on the color temperature of emission and micromorphology of YVO4∶Dy3+ is slight.

Photoluminescence Properties and Energy Transfer from Ce^(3+) to Tb^(3+) in Zn_2SiO-_4 Host

Zn2Si O4︰Tb^3＋, Zn2 Si O4︰Ce^3＋, Zn2 Si O4︰Tb^3＋, Ce^3＋ phosphors were prepared by solidstate reaction at 1 150 ℃ for 2h under a weak reducing atmosphere. Moreover, the XRD patterns and photoluminescence spectra were recorded and the effects of Tb3＋ and Ce3＋ concentration on the luminescent properties of as-synthesized phosphors were investigated. The emission spectra under ultraviolet light（333 nm） radiation showed a dominant peak at 542 nm attributed to the 5D4→7F5 transition of Tb^3＋, which was enhanced significantly（about 45 times） by the co-doping of Ce^3＋, indicating that there occurred an efficient energy transfer from Ce^3＋ to Tb^3＋. According to the Dexter＇s energy transfer formula of multipolar interaction, it was demonstrated that the energy transfer between Ce3＋ and Tb3＋ was due to the electric dipolar-dipolar interaction of the resonance transfer.

用Ce^(3+):YVO_4晶体荧光粉与蓝光LED制造自然白光LED

本文报导了通过结合自行制备的掺铈钒酸钇晶体(Ce3+:YVO4)荧光粉与InGaN／GaN蓝光发光二极管(LED)结合而得的白光发光二极管(W-LED)。在室温、正向电压3.5V、正向电流20mA时W-LED的CIE色坐标为(0．32,0．37),接近纯白色(0．33,0．33)。

Study on white-light emission and light-emitting mechanism of hydrothermally synthesized YVO_4:1 mol.%Dy^(3+),x mol.%Eu^(3+) phosphor powders

White light-emitting YVO4:1 mol.%Dy3+,x mol.%Eu3+ phosphor powders with order morphology and well crystallization were hydrothermally synthesized at 180°C. The microstructure, white-light emission, and light-emitting mechanism of the powders were carefully studied using X-ray diffractometry, scanning electron microscopy and photoluminescence spectra. The excitation and emission spectra of the phosphor powders indicated the coexistence of efficient energy transfer from Eu3+ to Dy3+ and inefficient en-ergy transfer from Dy3+ to Eu3+ besides the energy transfer from VO43– to Eu3+. Increasing the Eu3+ concentration initially enhanced and then weakened the luminescent intensity of Dy3+. The white-light emissions of YVO4:1 mol.%Dy3+,xmol.%Eu3+ phosphor pow-ders were both related to the energy transfer between VO43– and Dy3+/Eu3+, as well as between Eu3+ and Dy3+. The inefficient energy transfer from Dy3+ to Eu3+ was first found.

Photoluminescence properties and energy transfer of a single-phased white-emitting NaAlSiO_4:Ce^(3+),Sm^(3+)phosphor

A series of tunable phosphors NaAlSiO_4：Ce^（3＋）,Sm^（3＋） were synthesized using a conventional high-temperature, solid-state method. Crystal structure, photoluminescence excitation, and emission spectra with fluorescence decay curves were investigated. Under UV excitation（325 nm）, NaAlSiO_4：Ce^（3＋）,Sm^（3＋） showed strong blue emission located at 444 nm and orange-reddish emission centered at 563, 601, 648 and 712 nm, stemming from the characteristic emission for 4f-5d transition of Ce^（3＋） and ~4G_（5/2）→~6H_J（J=5/2, 7/2, 9/2, 11/2） transition of Sm^（3＋）, respectively. In addition, we studied the detailed energy transfer process between Ce^（3＋） and Sm^（3＋） and found that it belonged to dipole-dipole resonance energy transfer. Furthermore, we noted that the white light emitting from the Ce^（3＋）, Sm^（3＋） co-doped phosphors with the color coordinate（x=0.313, y=0.283） could be observed under 325 nm excitation, which was close to the ideal white light（x=0.33, y=0.33）. The results indicated that this phosphor has a potential application as a single-phased alumino-silicate phosphor for ultraviolet white light-emitting diodes（UV-WLEDs）.

LiZnPO_4:Tb^(3+),Ce^(3+) green phosphors with high efficiency

Tb^3＋ and Ce^3＋ co-activated LiZnPO4 phosphors with high luminescence efficiency were synthesized by a high temperature solid-state reaction at 1000 ℃ for 3 h. The XRD patterns, photoluminescence spectra and SEM were recorded and the effects ofTb^3＋and Ce^3＋ concentration, sintering condition on the luminescent properties of as-synthesized phosphors were investigated. The emission spectra under ultraviolet （200-300 nm） radiation showed a dominant peak at 543 nm attributed to the ^5D4→^7F5 transition of Tb^3＋, which was greatly enhanced by the co-doping of Ce^3＋, indicating that there occurred an efficient non-radiative energy transfer from Ce^3＋ to Th^3＋. The optimal doping concentrations of Tb^3＋ and Ce^3＋ were determined to be 9% and 10%, respectively.

Color-tunable Ca10Na(PO4)7：Ce^3＋/Tb^3＋/Mn^2＋ phosphor via energy transfer

A series of Ca10Na(PO4)7:Ce3+/Tb3+/Mn2+(CNPO:Ce3+/Tb3+/Mn2+) phosphors with high brightness were synthesized by high-temperature solid-state method. X-ray diffraction(XRD), scanning electron microscopy(SEM), diffuse reflectance spectra(DRS), photo luminescence(PL) spectra, luminescence decay curves and thermally stability were performed to characterize the as-prepared samples. For Ce3+-doped samples, an intense and broad band emission is present under 265 nm excitation. When Ce3+and Tb3+are codoped, energy transfer(ET) process from Ce3+ to Tb3+ is demonstrated with electric dipole-dipole interaction. The internal and external quantum efficiencies(QEs) of CNPO:0.15 Ce3+, 0.04 Tb3+, 0.005 Mn2+are measured to 76.79% and 54.11% under 265 nm excitation and temperature-dependent PL intensity can remain 51.78% at 150 ℃ of its initial intensity at 25 ℃. It is indicated that single-phased white lightemitting CNPO:Ce3+/Tb3+/Mn2+phosphor can serve as a promising phosphor for illumination devices.

白光LED用VO_4:Ce^(3+)荧光粉的制备与表征

白光LED中YAG荧光粉专利权为日本Nichia所有,各国研究者为了规避专利,争相研究替代产品。本文首次采用高温固相法制备了YVO4:Ce3+荧光粉,对不同Ce3+掺杂浓度下XRD图样与国际标准衍射卡对比后发现在1100℃保温9小时合成的Ce3+:YVO4为四方晶系结构,随保温时间延长,结晶程度更好,但时间再长时,结晶变化已不大。荧光光谱表明,激发光谱为双峰结构,主峰在232nm和403nm。发射光谱为一宽带,峰值在424nm附近。发现最佳Ce3+掺杂浓度为5mol%。结论是Ce3+:YVO4荧光粉可以满足与蓝光LED复合产生自然白光的要求。

A novel blue-purple Ce^(3+) doped whitlockite phosphor:Synthesis,crystal structure,and photoluminescence properties

At present,the rare earth(RE) ions doped phosphors have attracted more and more attention because of their excellent properties.In this paper,a series of novel blue-purple β-Ca_(3)(PO_(4))_(2):Ce^(3+) phosphors were synthesized by a high temperature solid phase method.The X-ray diffraction(XRD),infrared spectrum,energy dispersive spectroscopy(EDS),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),photoluminescence excitation and emission spectra were used to investigate the crystal structure,composition and the luminescent properties of the resulting samples.The phosphor shows a strong absorption in the ultraviolet band.Under the excitation of 269 nm,the phosphor emits a strong purple fluorescence ranging from 360 to 520 nm.When Ce^(3+) doping content is 0.07 mol,the strongest luminescence intensity is reached,and the concentration quenching mechanism is dipole-dipole(d-d)interaction for Ce^(3+) based on Dexter theory.

掺铈钒酸钇荧光粉的合成及其光谱特性

首次采用高温固相法制备了YVO4∶Ce3+荧光粉,对不同Ce3+掺杂浓度下XRD图样与国际标准衍射卡对比后发现在1100℃保温9 h合成的Ce3+∶YVO4为四方晶系结构,随保温时间延长,结晶程度更好,但时间再长时,结晶变化已不大.荧光光谱表明,激发光谱为双峰结构,主峰在232,403 nm.发射光谱为一宽带,峰值在424nm附近.还发现,最佳Ce3+掺杂质量浓度为5%.研究认为Ce3+∶YVO4荧光粉可以满足与蓝光LED复合产生自然白光的要求.