Luminescence Properties of Eu~(2 ) and Mn~(2 ) Co-Doped Ca_8Mg(SiO_4)_4Cl_2

The green phosphor for white LED, Ca8Mg(SiO4)4Cl2∶Eu2+, Mn2+, was synthesized by high temperature solid state reaction under reducing atmosphere. During the process of the phosphor prepared, the excess CaCl2 can improve the intensity of emission. The experimental results indicate that there is an effective energy transfer from Eu2+ to Mn2+in Ca8Mg(SiO4)4Cl2 host. This kind of energy transfer may be due to resonance transfer, and this energy transfer is limited.     

Intense blue-emitting Ca₂PO₄Cl:Eu²⁺ phosphor for near-ultraviolet converting white light-emitting diodes

A blue phosphor Ca2PO4Cl:Eu2+(CAP:Eu2+) was synthesized by solid state reaction.The Ca2PO4Cl:Eu2+ exhibited high quantum efficiency and excellent thermal stability.The luminescent intensity of Ca2PO4Cl:Eu2+ was found to be 128% under excitation at 380 nm,149% under 400 nm,and 247% under 420 nm as high as that of BaMgAl10O17:Eu2+.The optimal doping concentration was observed to 11 mol.% of CAP:Eu2+.The energy transfer between Eu2+ ions in CAP were occurred via electric multipolar interaction,and the critical transfer distance was estimated to be 1.26 nm.A mixture of blue-emitting Ca2PO4Cl:Eu2+,green-emitting(Ba,Sr)2SiO4:Eu2+ and red-emitting CaAlSiN3:Eu2+ phosphors were selected in conjunction with 400 nm chip to fabricate white LED devices.The average color-rendering index Ra and correlated color temperature(Tc) of the white LEDs were found to be 93.4 and 4590 K,respectively.The results indicated that it was a promising candidate as a blue-emitting phosphor for the near-UV white light-emitting diodes.     

Luminescence and Preparation of LED Phosphor Ca8Mg(SiO4)4Cl2:Eu2+

Calcium magnesium chlorosilicate doped by europium, Ca8Mg(SiO4)4Cl2:Eu2 , was prepared by the solid state reaction at high temperature. The compound obtained is pure Ca8Mg(SiO4)4Cl2 phase with cubic structure. Its average particle size is 5 μm, and it has good dispersity and morphological form. The excitation spectrum of Ca8Mg(SiO4)4Cl2:Eu2 is a wide band, which covers from 270 to 480 nm. The emission spectrum is also a wide band peaked at 510 nm. The luminescent intensity reaches to the maximum when the concentration of Eu2 is 2%. The wavelength of emission and excitation of the phosphor with various Eu2 contents keeps constant. This spectrum range matches violet and blue LED chips very well, and its strong luminescence intensity is suitable for a green phosphor of tricolor phosphor of white light LED.     

Luminescent properties of Ca2SiO4:Eu3+ red phosphor for trichromatic white light emitting diodes

The luminescent properties of Eu3 doped Ca2SiO4 red phosphors synthesized by the flux fusion reaction method were investigated. It was found that the excitation spectrum included two regions: the weak excitation band below 325 nm and strong narrow peaks above 325 nm. The main peak of the excitation band was located at 400 nm. The peaks located at 290 nm were assigned to the combination of the charge transfer transition of O-Eu, peaks above 325 nm (325, 385, 400, 470, 511, and 539 nm) were assigned to the f–f transitions of Eu3 . The emission spectrum was dominated by the red peak located at 612 nm due to the electric dipole transition of 5D0–7F2. In addition, the ef- fects of the Eu3 content and charge compensators of Li , Na , K , and Cl– ions on the emission intensity were investigated. The experiment results suggested that the strongest emission was obtained when the concentration of the Eu3 ions was 0.3 mol–1, and Li ions gave the best improvement to enhance the emission intensity. Ca2SiO4:Eu3 , Li was thus suitable for low-cost trichromatic white light emitting diodes (WLED) based on UV InGaN chip.     

Tunable luminescence of Ce3+/Li+,Eu2+ co-doped Ca4(PO4)2O phosphor for white light emitting diodes

Phosphors Ca4(PO4)2O:Ce3+/Li+,Eu2+ were prepared by solid state reaction successfully, and characterized by X-ray diffraction, UV-Vis spectrometer and photoluminescence spectrometry. The as-prepared phosphors exhibited strong absorption in the UV-visible region and dual-emission bands centered at approximately 460 and 630 nm. Energy transfer from Ce3+ to Eu2+ was also observed. By varying the excitation wavelength, these new phosphors exhibited tunable emissions from blue to white and then to yellow, making them potential candidates as UV-convertible phosphors for white light emitting diodes.     

A potential single-phased white-emitting LiBaBO3:Ce3+,Eu2+ phosphor for white LEDs

Ce3+/Eu2+ co-doped LiBaBO3 phosphor was synthesized by high temperature solid-state reaction method, and its luminescent character- istics were investigated. The hues of the LiBaBO3:Ce3+, Eu2+ phosphor varies from blue to white and eventually to yellow-green by properly tuning the Ce3+/Eu2+ ratio. Under UV excitation, white light was generated by coupling blue and yellow-green emission bands attributed to Ce3+ and Eu2+ emissions, respectively. The luminous efficacy of LiBaBO3:1%Ce3+, 2%Eu2+ calculated from ...     

Enhancement of red to orange emission ratio of YPO4：Eu3＋,Ce3＋ and its dependence on Ce3＋ concentration

Eu3+ and Ce3+ co-doped YPO4 microspheres were synthesized by hydrothermal method without template. The emission spectra showed that the red emission centered at 618nm could be readily increased relatively to the orange emission centered at 590nm by controlling the doping concentration of Ce3+ ion. The investigation based on excitation spectra and decay curves demonstrated that the doped Ce3+ ions took two efficient energy transfers to Eu3+ ions and affected the lifetime of the emission states of Eu3+ ions so that the emission spectra of Eu3+ ion were accordingly tuned with the Ce3+ content increasing. This controllable red (5D0→7F2) to orange ( 5D0→7F1) emission ratio of YPO4:Eu3+,Ce3+ made it very promising for encoded anti-fake labels and bio-labels.     

Luminescent Properties of Green Phosphor Ca8Mg（SiO4 ）4 Cl2：EU^2＋ , DY^3＋ for LED Applications

The new phosphor calcium magnesium chlorosilicate, codoped with Eu^2＋ and Dy^3＋, was synthesized with the help of the high temperature solid state reaction in reducing atmosphere. The excitation and emission spectra were very similar to that of Ca8Mg（SiO4）4Cl2 ：Eu^2＋, and the Dy^3＋ concentration influenced the emission intensity of this phosphor. The intensity of Eu^2＋ and Dy^3＋ codoped CMSC was stronger than that of Eu^2＋ singly doped CMSC. The emission spectrum of the Dy^3＋ ion overlapped the absorption band of the Eu^2＋ ion, indicating that an energy transfer from Dy^3＋ to Eu^2＋ took place in CMSC：Eu^2＋, Dy^3＋ phosphor. The mechanism of the energy transfer from Dy^3＋ tO Eu^2＋, in this phosphor, might be resonant energy transfer.     

Combustion synthesis of Ce~（3＋）, Eu~（3＋） and Dy~（3＋） activated NaCaPO_4 phosphors

The preparation of NaCaPO4 doped with rare earth (RE) ions Ce3+, Eu3+ and Dy3+ by combustion method was described. Under UV excitation (251 nm) of NaCaPO4:Ce3+ showsd emission (367 nm) in UV range. When NaCaPO4:Dy3+ phosphor was excited at 349 nm, the emission spectrum showed intense bands at 482 nm (blue) and 576 nm (yellow). In Eu activated NaCaPO4 phosphor, the emission spectrum showed a dominant peak at 594 nm (orange) while others were at 614 and 621 nm (red) when excited at 393 nm. The prepared phosph...     

Effect of different dopants on the long lasting phosphorescence behavior of CaTiO_3：Pr~（3＋）

In order to improve the luminescence properties of CaTiO3:Pr3+, a series of CaTiO3:Pr3+, such as CaTi0.97Nb0.03O3:Pr3+, Ca0.8Zn0.2TiO3: Pr3+, Ca0.8Zn0.2Ti0.97Nb0.03O3:Pr3+ and B3+-doped Ca0.8Zn0.2Ti0.97Nb0.03O3: Pr3+ were prepared through conventional solid state reaction method. The results of the photoluminescence excitation and emission spectra showed that all the samples emitted red phosphorescence at 612 nm originating from 1D2 to 3H4 emission of Pr3+ under the 337 nm excitation. When examined by the X-ray diffraction (XRD), all the samples presented a predominant phase of CaTiO3 (JCPDS# 42-423) except Zn2+-doped samples which also revealed another phase of Zn2Ti3O8 (JCPDS# 73-579). The results of the afterglow decay curves showed that co-doping Zn2+ ions, Nb5+ ions or adding a small amount of B3+ into Ca0.8Zn0.2Ti0.97Nb0.03O3:Pr3+ were effective in improving the photoluminescence properties of CaTiO3:Pr3+ phosphor. Thermoluminescence results showed that the trap existing in all the samples was the same as in CaTiO3:Pr3+ and doping singly Nb5+ or Zn2+ hardly changed the trap depth but co-doping Nb5+ and Zn2+ could modify the trapping level from 0.63 to 1.26 eV distinctively. In addition, adding a certain amount of B3+ into CTO-PZN could also deepen the trap depth.     

Study on Ca8Mg(SiO4)4Cl2:Eu2+ Doped with Sr2+

Ca8Mg(SiO4)4Cl2:Eu2 phosphor doped with Sr2 cation for Ca2 partially, was synthesized by solid-state reaction at high temperature under reducing atmosphere, and its luminescent properties were investigated. The experimental results indicate that the emission intensity of the phosphor increases after being doped with a few amount of Sr2 ion. The emission peak of the phosphor blue shift to about 464 nm when the phosphor is doped with large quantity of Sr2 ions. The excitation spectrum indicates that the phosphor can be well excited by UV and blue light from 300 to 460 nm, and the phosphor was fitted well for the excitation by UV or blue-LED.     

Luminescent properties of MMgP_2O_7：Eu~（3＋）（M=Ca,Sr,Ba） phosphor

A series of red phosphors Eu3+-doped MMgP2O7(M=Ca,Sr,Ba) were synthesized by solid-state reaction method.X-ray powder diffraction(XRD) analysis confirmed the formation of pure CaMgP2O7,SrMgP2O7 and BaMgP2O7 phase.Photoluminescence spectra of MMgP2O7(M=Ca,Sr,Ba):Eu3+ phosphors showed a strong excitation peak at around 400 nm,which was coupled with the characteristic emission(350-400 nm) from UV light-emitting diode.The CaMgP2O7:Eu3+,SrMgP2O7:Eu3+ and BaMgP2O7:Eu3+ phosphors showed strong emission bands peaking at 612,593 and 587 nm,respectively.Due to the difference of the ion sizes between Ba2+(0.142 nm),Sr2+(0.126 nm),Ca2+(0.112 nm),Mg2+(0.072 nm) and Eu3+(0.107 nm),Eu3+ ions were expected to substitute for different sites in CaMgP2O7,SrMgP2O7 and BaMgP2O7 lattice.     

Rare earth double activated phosphors for different applications

For the purpose of development of highly energy-efficient light sources,one needs to design highly efficient green,red and yellow phosphors,which are able to absorb excitation energy and generate emissions.In this contribution,we present our results on producing some efficient phosphors with improved luminescence properties.Using double activation,energy could be transferred from one luminescent activator to the other one,resulting in more efficient or brighter device operation.Co-activators could be added to a host material to change the color of the emitted light.The incorporation of Eu3+ or Tb3+ ions into the CaWO4 crystal lattice modified the luminescence spectrum due to the formation of the emission centers that generated the specific red and green light.Very efficient new red phosphors based on YNbO4 and doped by Eu3+,Ga3+,Al3+ allowed recommending these materials as good candidates for different applications including LED and X-ray intensifying screens.For double activated TAG with Ce3+ and Eu3+ and for different mole ratios of Ce/Eu,the color temperature changed from 5500 K(0.331,0.322) up to 4200 K(0.370,0.381) and the light became "warmer".Application of TAG:Ce,Eu in the light emitting device showed better chromaticity coordinates of luminescence and color rendering index of LEDs.     

Long Lasting Phosphorescence in Eu2+ and Ce3+ Co-Doped Strontium Borate Glasses

Long lasting phosphorescence (LLP) was observed in Eu2+, Ce3+ co-doped strontium borate glasses prepared under the reducing atmosphere due to the emission of both Eu2+ and Ce3+. The methods of photoluminescence, thermoluminescence and phosphorescence were used to study the samples, and possible mechanism was suggested. The co-doping of Ce3+ ions poisoned the phosphorescence emission of Eu2+ because of the competition to obtain the trapped electron. The phosphorescence of Ce3+ in the sample decays more quickly than that of Eu2+, which is suggested for the reason that the emission energy of Ce3+ is higher or the distance between Ce3+ and electron traps of the glasses is longer.     

Luminescence properties of BaB8O13：Eu under UV and VUV excitation

The phosphor BaB8O13:Eu3+ were synthesized by solid-state reaction, and their luminescent properties were studied under 254 and 147 nm excitation. The excitation spectrum showed two broad bands in the range of 100-300 nm: one was the host lattice absorption with the maxima at 160 nm and the other was Ba-O absorption overlapped with the CT band of Eu3+, which indicated that the energy of the host lat-tice absorption could be efficiently transferred to the Eu3+. The overlapped bands were tended to separate when monitored by different wave-length, which indicated that at least two Ba2+ sites were available in BaB8O13. The emissions of Eu3+ (612 nm) and Eu2+ (405 nm) were both observed in the emission spectra of BaB8O13:Eu3+ under the excitation of either 254 or 147 nm. With the doping concentration of Eu3+ in-creasing, the 612 nm emission was enhanced while 405 nm emission was decreased under 254 nm excitation, which was due to the persistent energy transfer from Eu2+ to Eu3+. While under 147 nm excitation, the 612 nm emission was quenched and the 405 nm emission was en-hanced. It was concluded that the preferential excitation of Eu2+ under 147 nm excitation was one of the reasons for this facts.     

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 ...     

Enhancement of photoluminescence of Ba2SiO4：Eu^2＋ by co-doping of La^3＋ or Y^3＋

Green light-emitting Ba2SiO4:Eu2+ phosphors co-doped with La or Y were synthesized by conventional solid-state reaction technique in reductive atmosphere (a mixture of 5% H2 and 95% N2). The results showed that the co-doping of La and Y could greatly enhance the fluorescence intensity of Ba2SiO4:Eu2+ phosphors. The optimum doping concentration expressed by the x value in (Ba0.985-1.5xREx)2SiO4: 0.03Eu2+ (RE=La or Y) was determined to be of 0.05. The excitation and emission peaks of all as-synthesized phosphors were wide bands. The excitation bands ranged from 250 to 400 nm, which matched well with the wavelength of near ultraviolet white light-emitting diodes (LED) chip and could be used as a potential candidate for the fabrication of white LED. The emission bands from 450 to 550 nm were typical 5d-4f transition emission of Eu2+ and displayed un-symmetry profiles because of the two substitution sites of Ba2+ with Eu2+.     

CaMoO_4∶Eu~(3+),M~+(M=Li,Na,K)粉体的制备与发光性能研究

采用溶胶-凝胶法制备了Ca_(1-1.5x)MoO_4∶xEu~(3+)和Ca_(0.5)MoO_4∶0.25Eu~(3+),M~+(M=Li,Na,K)荧光粉,并对样品的物相结构、颗粒形貌及发光性能进行了分析。结果表明,样品属于四方晶系,颗粒接近八面体形状,大小为2~3μm。激发光谱显示,样品的激发中心分别位于364 nm、386 nm、396 nm、419 nm和466 nm,最大激发峰值位于396 nm。在396 nm近紫外光激发下,样品的发射中心分别位于596 nm、616 nm、656 nm、704 nm,特征发射峰为616 nm,Eu3+离子掺杂浓度为25%(体积分数)时发光强度最强,引入的3种电荷补偿剂M~+(M=Li,Na,K)中,Li+对发光强度的提高最为显著。     

Luminescent properties of red phosphors K2Ba（MoO4）2：Eu3＋ for white light emitting diodes

K2Ba(MoO4)2:Eu3+ phosphors were synthesized by solid-state reaction. The emission and excitation spectra of K2 Ba(MoO4)2:Eu3+ phosphors exhibited that the phosphors could be effectively excited by near ultraviolet (394 nm) and blue (465 nm) light, and emitted red light at 616 nm. The influence of Eu3+concentration, sintering temperature and charge compensators (K+, Na+ or Li+ ) on the emission intensity were investigated. The results indicated that concentration quenching of Eu3+ was not observed within 30mol.% Eu 3+, 600 oC was a suitable sintering temperature for preparation of K2 Ba(MoO4)2:Eu3+phosphors, and K+ ions gave the best improvement to enhance the emission intensity. The CIE chromaticity coordinates of K2 Ba(MoO4)2:0.05Eu3+phosphor were calculated to be (0.68, 0.32), and color purity was 97.4%.     

Energy transfer from Ce~(3+) to Tb~(3+) and Eu~(3+) in zinc phosphate glasses

Ce3+,Eu3+ and Tb3+ singly doped and Ce3+/Eu3+ and Ce3+/Tb3+ co-doped zinc phosphate glasses were prepared by sintering P2O5,ZnO,Ce2(C2O4)3·10H2O and Eu2O3/Tb4O7 mixtures at 1200 °C in the air for 2 h and then annealing at 450 °C for 10 h.The obtained glasses were homogeneous and transparent.The glasses without Ce3+ were colorless and those with Ce3+ showed slightly yellow.The singly doped glasses showed strong emissions and excitations from doped trivalent rare earth ions.Strong energy transfer from Ce3+ to Tb3+ was observed for Ce3+/Tb3+ coped samples.There were also some very weak evidences for the energy transfer from Ce3+ to Eu3+.