Luminescence characteristics of Eu^(3+) activated borate phosphor for white light emitting diode

In this paper, the Sr3Y2 （BO3）4 ：Eu^3＋ phosphor was synthesized by high temperature solid-state reaction method and the luminescence characteristics were investigated. The emission spectrum exhibits one strong red emission at 613 nm corresponding to the electric dipole 5^Do-7^F2 transition of Eu^3＋ under 365 nm excitation, this is because Eu^3＋ substituted for Y^3＋ occupied the non-centrosymmetric position in the crystal structure of Sr3Y2（BO3）4. The excitation spectrum indicates that the phosphor can be effectively excited by ultraviolet （254 nm, 365 nm and 400 nm） and blue （470 nm） light. The effect of Eu^3＋ concentration on the red emission of Sr3Y2（BO3）4 ：Eu^3＋ was measured, the result shows that the emission intensities increase with increasing Eu^3＋ concentration, then decrease. The Commission Internationale del＇Eclairage chromaticity （x, y） of Sr3Y2（BO3）4 ：Eu^3＋ phosphor is （0.640, 0.355） at 15 mol% Eu^3＋.

A novel yellow phosphor for white light emitting diodes

This paper reports that a novel yellow phosphor, LiSrBO3：Eu2＋, was synthesized by the solid-state reaction. Thc excitation and emission spectra indicate that this phosphor can be effectively excited by ultraviolet （360 and 400 nm） and blue （425 and 460 nm） light, and exhibits a satisfactory yellow performance （565 nm）. The role of concentration of Eu2＋ on the emission intensity in LiSrBO3 is studied, and it is found that the critical concentration is 3 mol%, and the concentration self-quenching mechanism is the dipole-dipole interaction according to the Dexter theory. White light emitting diodes were generated by using an InGaN chip （460 nm or 400 nm） with LiSrBO3：Eu2＋ phosphor, the CIE chromaticity is （x = 0.341, y =0.321） and （x = 0.324, y = 0.318）, respectively. Therefore, LiSrBOa：Eu^2＋ is a promising yellow phosphor for white light emitting diodes.

Structure and luminescence of Ca_2Si_5N_8:Eu^(2+) phosphor for warm white light-emitting diodes

We have synthesized Ca2Si5N8：Eu^2＋ phosphor through a solid-state reaction and investigated its structural and luminescent properties. Our Rietveld refinement of the crystal structure of Ca1.9Eu0.1Si5N8 reveals that Eu atoms substituting for Ca atoms occupy two crystallographic positions. Between 10 K and 300 K, Ca2Si5N8：Eu^2＋ phosphor shows a broad red emission band centred at -1.97 eV-2.01 eV. The gravity centre of the excitation band is located at 3.0 eV 3.31 eV. The centroid shift of the 5d levels of Eu^2＋ is determined to be -1.17 eV, and the red-shift of the lowest absorption band to be - 0.54 eV due to the crystal field splitting. We have analysed the temperature dependence of PL by using a configuration coordinate model. The Huang-Rhys parameter S = 6.0, the phonon energy hv = 52 meV, and the Stokes shift △S = 0.57 eV are obtained. The emission intensity maximum occurring at -200 K can be explained by a trapping effect. Both photoluminescence （PL） emission intensity and decay time decrease with temperature increasing beyond 200 K due to the non-radiative process.

Synthesis of CaO-SiO_2-B_2O_3∶Sm_2O_3 Glasses and Luminescent Properties of Sm^(3+)

CaO-SiO2-B2O3 ：Sm2O3 glasses were synthesized in air atmosphere with conventional high temperature process. The optimal temperature of synthesis, the absorption spectrum and the luminescent properties of the glasses were studied. The fluorescence spectrum of Sm^3＋ was observed in CaO-SiO2-B2O3 ： Sm2O3 glasses. The fluorescence spectrum of the sample has three major emission bands peaking at 568, 605 and 650 nm respectively. The strongest emission band peak at 605 nm. It is concluded that the emissions were caused by the f-f transition of the 4f electrons of Sm^3＋. The emission bands peaking at 568, 604 and 650 nm correspond to the ^4G5/2→^6H5/2 transition, ^4G5/2→^6H7/2 transition and ^4G5/2→^6H9/2 trasition respectively. The luminescent properties of CaO-SiO2-B2O3 glasses indicate that the glass can convert the ultraviolet in the sunlight into red light, thus increasing the intensity of red light. The luminescent properties of these glasses may be used to make kinds of light-conversion glass for agriculture.

Rational Design of Star-shaped Molecules with Benzene Core and Naphthalimide Derivatives End Groups as Organic Light-emitting Materials

A series of star-shaped molecules with benzene core and naphthalimides derivatives end groups have been designed to explore their optical,electronic,and charge transport properties as charge transport and/or luminescent materials for organic light-emitting diodes（OLEDs）. The frontier molecular orbitals（FMOs） analysis has turned out that the vertical electronic transitions of absorption and emission are characterized as intramolecular charge transfer（ICT）. The calculated results show that the optical and electronic properties of star-shaped molecules are affected by the substituent groups in N-position of 1,8-naphthalimide ring. Our results suggest that star-shaped molecules with n-butyl（1）,benzene（2）,thiophene（3）,thiophene S？,S？-dioxide（4）,benzo[c][1,2,5]thiadiazole（5）,and 2,7a-dihydrobenzo[d]thiazole（6） fragments are expected to be promising candidates for luminescent and electron transport materials for OLEDs. This study should be helpful in further theoretical investigations on such kind of systems and also to the experimental study for charge transport and/or luminescent materials for OLEDs.

Synthesis and Properties of Eu_(3+) Activated Strontium Molybdate Phosphor

In order to prepare fluorescent material for white Light Emitting Diodes （LEDs）, a new Eu^3＋ activated molybdate phosphor SrMoO4 was fabricated with solid-state method. X-ray diffraction （XRD） showed that the doping of trivalent europium ion reduced the lattice parameters. The excitation and emission spectra indicated that this phosphor could be excited effectively by the visible light, and then emitted red light with the peaks located at 616 and 624 nm. The influence of Eu^3＋ concentration on the luminescent properties of Eu^3＋ doped SrMoO4 was investigated and the 25% （mole fraction） was the appropriate molar concentration. The reaction time and temperature had obvious effect on the luminescent properties. The luminescent intensity reached the strongest when it was sintered at 800 ℃ for 3 h.

A novel white emitting phosphor Ca_2PO_4Cl:Dy^(3+): luminescence, concentration quenching and thermal stability

A novel white emitting phosphor Ca2PO4Cl：Dy^3＋ was synthesized by a solid state method. The luminescence, concentration quenching and thermal stability of Ca2PO4Cl：Dy^3＋ were investigated. Ca2PO4Cl：Dy^3＋ showed three emission peaks, which were located at 483, 575 and 660 nm. Though the ratio of yellow to blue emission intensities showed a similar value, the intensities of yellow and blue peaks were influenced by Dy^3＋ concentration, and the concentration quenching effect was observed. The emission intensity of Ca2PO4Cl：Dy^3＋ as a function of temperature was explored and the emission intensity（at 150 °C） of Ca2PO4Cl：Dy^3＋ was 90.0% of the value at 25 °C, and activation energy was 0.18 eV. The results indicated that Ca2PO4Cl：Dy^3＋ might be conducive to development of white LEDs.

溶胶-凝胶法制备Gd_(4)Ga_(2)O_(9):Dy^(3+)白光发射荧光粉及其性能

通过溶胶-凝胶法制备了具有白光发射的Gd_(4)Ga_(2)O_(9):x%Dy^(3+)荧光粉,利用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)、紫外-可见漫反射光谱(UV-Vis DRS)和荧光光谱等对产物的物相结构、形貌、组分和光学性能进行研究,并分析了Dy^(3+)掺杂量对样品的影响。XRD结果表明,所制备的样品为Dy^(3+)掺杂的Gd_(4)Ga_(2)O_(9)单斜晶体和少量Ga_(2)O_(3)杂质相的混合物。紫外-可见漫反射光谱结果表明制备的Dy^(3+)掺杂Gd_(4)Ga_(2)O_(9)晶体是一种光学带隙为5.29 eV的直接带隙半导体。荧光检测结果表明Dy^(3+)掺杂Gd_(4)Ga_(2)O_(9)荧光粉可被属于Gd^(3+)激发带的275 nm紫外光有效激发,并在490 nm和575 nm附近分别发射出属于Dy^(3+)的^(4)F_(9/2)→^(6)H_(15/2)和^(4)F_(9/2)→^(6)H_(13/2)跃迁的蓝色和黄色的强烈光,证实在Gd_(4)Ga_(2)O_(9):Dy^(3+)样品中存在显著的由Gd^(3+)到Dy^(3+)的能量传递发光现象。同时,对其发光机制进行了讨论。样品的发光强度随着Dy^(3+)掺杂量的变化而变化,同时影响着样品的发光颜色,Dy^(3+)掺杂量为1.5%和2%时制备的荧光粉可在紫外光激发下分别发射出CIE色坐标为(0.3362,0.3512)和(0.3381,0.3523)、相关色温为5340 K和5263 K的白色光。研究结果表明Gd_(4)Ga_(2)O_(9):Dy^(3+)是一种潜在的紫外光激发白光发射荧光材料。

Bi^(3+)、Eu^(3+)共掺杂La_(4)GeO_(8)荧光粉的制备及可调发光

为了开发出高效稳定的单一基质白光发射荧光材料,本工作通过高温固相法成功合成了一系列La_(4)GeO_(8)∶Bi^(3+),Eu^(3+)荧光粉样品,并通过X射线衍射、室温光谱、变温光谱等手段研究了实验样品的结构与发光性能。研究发现,Bi^(3+)离子在该结构中占据两种不同的格位(Bi^(3+)(Ⅰ)和Bi^(3+)(Ⅱ)),且在紫外光激发下呈现两个峰值分别在475 nm和620 nm的宽带发射。对于Bi^(3+)、Eu^(3+)共掺样品,由于Bi^(3+)(Ⅰ)与Eu^(3+)之间的竞争吸收、Bi^(3+)(Ⅰ)至Bi^(3+)(Ⅱ)以及Bi^(3+)(Ⅱ)至Eu^(3+)的能量传递作用,可实现蓝色至红色、橙红色至红色的可调发光。特别地,样品La_(4)GeO_(8)∶0.07Bi^(3+),0.06Eu^(3+)在313 nm光激发下可获得CIE值为(0.335,0.319)的优异白色发光。此外,该白光发射材料具有较佳的发光热稳定性,当温度升高至380 K时,发光积分强度仍然为室温的59%,表明其在白光二极管上具有潜在的应用价值。

SrLaLiTeO_(6):Dy^(3+),Eu^(3+)荧光粉的制备及发光性能研究

白光发光二极管(LED)的商业合成方案缺少红光成分,导致合成的白光色温较高、显色性差,因此开发性能优异的单相暖白光荧光粉成为白光LED领域研究的重要课题。以Dy^(3+)和Eu^(3+)为掺杂剂,SrLaLiTeO_(6)(SLLT)为基质,采用固相反应法制备了SrLaLiTeO6:Dy^(3+),Eu^(3+)无机荧光粉,并通过X射线衍射仪、荧光分光光度计和色度坐标分析荧光粉的晶体结构及光学性能。结果表明:Dy^(3+)和Eu^(3+)成功进入SLLT晶体,无杂质产生;SLLT:0.07Dy^(3+),yEu^(3+)荧光粉在351 nm激发下能够同时发射蓝、黄、红光,证明了Dy^(3+)和Eu^(3+)之间存在能量传递,弥补了单掺Dy^(3+)荧光粉缺乏红色发射的缺陷;Eu^(3+)离子最佳掺杂浓度为0.05,此时的色度坐标为(0.391 9,0.380 9),色温为3 733 K,接近暖白光区域。因此,SrLaLiTeO_(6):Dy^(3+),Eu^(3+)荧光粉是一种性能优异的暖白光LED荧光粉。

三联吡啶苯桥连β-二酮配体调控3d-4f能量传递及单分子白光研究

设计并制备了三联吡啶单、双和三苯桥连β-二酮配体(SL3、DL3和TL3)及其3d-4f配合物(SL3-Zn-Eu、DL3-Zn-Eu和TL3-Zn-Eu)。研究发现,SL3-Zn-Eu和DL3-Zn-Eu在紫外激发下通过三重态能量传递敏化Eu3+的特征红光,两者色度坐标均为(0.67,0.33),主要原因是3d和4f中心距离更近,更有利于3d-4f的能量传递。然而,TL3-Zn-Eu结构中3d和4f中心距离更远,且随着桥连苯环数量的增加导致桥连苯平面扭曲,使3d→4f能量传递速率减低和单重态能量传递敏化Eu^(3+)发光。从荧光光谱中可以检测到Eu^(3+)特征红光和TL3-Zn的残余青光,其发光颜色落在白光区域,色度坐标为(0.30,0.29)。总之,本文设计的3d-4f配合物随着桥连苯数的增加,可以改变分子共轭性和3d→4f间距离,从而调节能量传递效率和传递机制,获得单分子发射白光材料。

用于W-LED照明材料Ce^(3+)/Tb^(3+)/Eu^(3+)共活化钆硼硅酸盐玻璃发光性能研究

以钆硼硅酸盐玻璃作为基质组成,采用高温烧结法制备了Ce^(3+)/Tb^(3+)/Eu^(3+)三掺杂发光玻璃。采用激发发射光谱、色度分析(CIE)等方法,对Ce^(3+)/Tb^(3+)/Eu^(3+)共掺杂钆硼硅玻璃的光学性质进行分析。根据光谱分析,稀土掺杂玻璃在改变Eu_(2)O_(3)浓度,调节到0.9 mol%时达到极值,再持续增加浓度,强度反而降低,这可能是由于浓度猝灭所致。对Ce^(3+)→Tb^(3+)、Tb^(3+)→Eu^(3+)的能量转移现象,利用发射光谱和荧光寿命进行了分析。当Ce^(3+)/Tb^(3+)/Eu^(3+)掺杂浓度比调整为0.6 mol%、0.45 mol%和0.9 mol%,并在380 nm处激发时,CIE显示坐标点为(0.3387,0.3276),近似于白光发射效果。

Single-phase full-color Ba_3Lu_2(SiO_4)_3:Eu^(2+) phosphor for white-light emitting diodes

we developed a new silicate-based full-color phosphor Ba3Lu2（SiO4）3：Eu2＋ through solid state reaction.The host crystal structure was isostructural with Ca3Y2（SiO4）3 instead of garnet-type.The phosphor absorbed near-ultraviolet light from 250 to 400 nm,which was very suitable for a color converter of white LED that used UV-LED as the primary light source.The photoluminescence peak wavelength of Ba3Lu2（SiO4）3：Eu2＋ was about 461 nm and a shoulder peak was around 522 nm,which resulted from the 5d-4f transition of the Eu2＋.The optimum concentration of Eu2＋ was 3.45 mol.% of Ba2＋ content in Ba3Lu2（SiO4）3 host.It is a promising candidate for application in white LED as a white light converter.

Luminescent properties of Ce^(3+)/Tb^(3+) co-doped glass ceramics containing YPO_4 nanocrystals for W-LEDs

Ce^3＋/Tb^3＋ co-doped transparent glass ceramics containing YPO4 nanocrystals were prepared using high temperature melting method,and their structural and luminous properties were investigated.XRD analysis and TEM images confirmed the existence of YPO4 nanocrystals in glass ceramics.The transmission spectra proved that the glass ceramics specimens still maintained a high transparency.Then the excitation and emission spectra of the Ce^3＋ and Tb^3＋ single-doped and co-doped glass and glass ceramics were discussed,which proved that the glass ceramics had better luminescent properties.Under the near ultraviolet（331 nm）excitation,the broadband emission located at 385 nm was observed which was ascribed to 5d→~2F（5/2） and ~2F（7/2） transition of Ce^3＋ ions.Several characteristic sharp peaks centered at 489,543,578 and 620 nm originated from the ~5D4 to ~7FJ（J=6,5,4,3）of Tb^3＋ ions.The decay time of Tb^3＋ ions at 543 nm and the relevant energy levels of Ce^3＋ ions and Tb^3＋ ions illustrated the transfer process from Ce^3＋ ions to Tb^3＋ ions.The best CIE chromaticity coordinate of the glass ceramics specimen was calculated as（x=0.3201,y=0.3749）,which was close to the NTSC standard values for white（x=0.333,y=0.333）.All the results suggested that the YPO^4-based Ce^3＋/Tb^3＋ co-doped glass ceramics could act as potential luminescent materials for white light-emitting diodes.

White light-emitting Ba0.05Sr0.95WO4:Tm3+Dy3+phosphors

Tm3＋ and Dy3＋） co-doped Ba（0.05）Sr0.95WO4 phosphors were synthesized by a low temperature combustion method. The structures of the samples were SrWO_4 phase and were identified by X-ray diffraction. The surface topographies of Ba_（0.05）Sr_（0.91）WO_4：0.01 Tm^（3＋） 0.03 Dy^（3＋） were tested by scanning electron microscopy. The particles are ellipsoid, and their average diameter is approximately 0.5 μm. The emission spectra of Ba_（0.05）Sr_（0.95）WO_4：Tm^（3＋） show a peak at 454 nm which belongs to the ~3 H_6→~1 D_2 transition of Tm^（3＋）, and the optimum doping concentration of Tm^（3＋） ions was 0.01. The emission spectra of Ba_（0.05）Sr_（0.95）WO_4：Dy^（3＋） consist of the ~4 F_（9/2）→~6 H_（13/2） dominant transition located at 573 nm, the weaker ~4 F_（9/_2→~6 H_（15/2） transition located at 478 and 485 nm. And the weakest ~4 F_（9/2）→~6 H_（11/2） transition located at660 nm, and the optimum doping concentration of Dy^（3＋） ions was 0.05. A white light is achieved from Tm^（3＋） and Dy^（3＋） co-doped Ba_（0.05）Sr_（0.95）MoO_4 crystals excited at 352-366 nm. With the doping concentration of Tm^（3＋） fixed at 0.01, the luminescence of Ba_（0.05）Sr_（0.95）MoO_4：Tm^（3＋）Dy^（3＋） is closest to standard white-light emissions when the concentration of Dy^（3＋） is 0.03; the chromaticity coordinates are（0.321,0.347）, and the color temperature is 6000 K.

Ce/Tb/Sm共掺杂CaO-B_2O_3-SiO_2发光玻璃的白光发射及其发光颜色调控

用高温熔融法制备了Ce/Tb/Sm三元共掺杂的CaO-B2O3-SiO2发光玻璃材料,并使用荧光分光光度计和CIE色度坐标对其光谱学和发光特性进行了研究.结果表明:在374nm激发下,在Ce/Tb/Sm三元共掺杂发光玻璃的发射光谱中同时观测到了蓝光、绿光和红橙光的发射带,这些发射带的混合实现了白光的全色发射显示.此外,Ce/Tb/Sm三元共掺杂发光玻璃的发光颜色随着Tb4O7含量的减小从绿光逐渐过渡到白光,显示出发光颜色的可调节性,极大地扩展了其在白光发光二极管中的应用.

Sr_2MgSiO_5:(Eu^(2+),Mn^(2+))单一基质白光荧光粉的发光性质

研究了Eu2+,Mn2+共激活的单一基质Sr2MgSiO5白光发光材料的发光性质。Eu2+中心形成峰值分别为459,555nm的特征宽带,而Eu2+中心向Mn2+中心的能量传递导致了峰值为678nm的发射,3个谱带叠加从而在单一基质中得到了白光。其激发光谱分布在250～450nm的波长范围,峰值位于390nm,可以被InGaN管芯产生的380～410nm辐射有效激发。Sr2MgSiO5:(Eu2+,Mn2+)是一种性能良好的单一基质白光发光二极管用荧光粉。

白光LED用钛酸盐红色荧光粉的研究进展

钛酸盐因具有优异的化学稳定性和光学性能而成为优异的发光基质材料,综述了钛酸盐作为白光LED用红色荧光粉的国内外研究进展。分别介绍了偏钛酸盐(MTiO3)型、正钛酸盐(M2TiO4)型和其他类型的钛酸盐红色荧光粉及其制备方法,并重点介绍了其光谱调控机理。对性能较好的荧光粉进行了重点推介,对钛酸盐红色荧光粉的发展趋势做了简要展望。

用于星上定标光源的LED筛选装置

考虑将发光二极管(LED)用作空间相机星上定标光源时对LED的发光一致性和稳定性的要求,研究了对市售LED产品进行试验和筛选的方法。分析了影响LED发光效率的因素及LED作为星上定标光源需要注意的问题,提出了将多只LED作为空间相机星上定标光源的筛选试验方案,并设计、研制了筛选装置。为了检验LED的工作稳定性和不同LED的发光一致性,该装置可同时监测多只LED的发光状态,并实现了无人值守操控和自动测量。利用该装置对某批次72只随机抽取的白光LED进行测试并根据测试数据对被筛选的白光LED进行了分析计算,结果显示,经过筛选的白光LED在连续点亮900h后,相对光强变化在1.5%左右。最后,从中筛选出符合光源要求的10只LED。

MgO对Sr_2SiO_4∶Eu^(2+)荧光粉发光性质的影响

通过在Sr2SiO4∶Eu2+荧光粉中加入MgO,提高了Sr2SiO4∶Eu2+荧光粉的蓝光和黄光发射带的发射强度,研究了MgO浓度对Sr2SiO4∶Eu2+荧光粉发光强度的影响。当Mg与Si的量比在1.0附近时,荧光粉的亮度较高,且发光颜色为白色。通过调节Sr2SiO4∶yEu2+,MgO荧光粉中Eu2+的掺杂浓度,可以调节荧光粉的发光颜色。用Sr2SiO4∶Eu2+,MgO和400 nm的InGaN管芯制备的白光LED,色坐标优于α'-Sr2SiO4∶Eu2+和β-Sr2SiO4∶Eu2+荧光粉制成的白光LED,显色指数和流明效率高于β-Sr2SiO4∶Eu2+和α'-Sr2SiO4∶Eu2+制成的白光LED。