Tuning of emission by effect of local symmetry in BaLaLiWO6:Dy3+/Eu3+ for WLEDs

The luminescence center energy transfer, crystal field strength, and covalency are limited by the crystal structure of the host and subsequently affect the luminescence efficiency, color, and intensity. Here, we report an excellent red phosphor BaLaLiWO₆:0.40Eu³⁺ and the dependence between symmetry and luminous performance. A model for changing symmetry is drawn by analyzing the Coulomb potential and structure for the application of a double-perovskite phosphor BLLWO: Dy³⁺, Eu³⁺ in white light LEDs. The addition of Dy³⁺/Eu³⁺ makes the W-O bond formed by the B-site and oxygen ion longer and the Li-O bond shorter, and the difference between the eight octahedral around the A-site is reduced, increasing the symmetry of the A-site. Local symmetry was successfully modulated by changing the Eu³⁺ concentration to control the Y/B ratio of Dy³⁺ and the R/O ratio of Eu³⁺ and smoothly achieved (0.382, 0.373) warm white light color coordinate. The phosphor has excellent thermal stability and still has 92.3% intensity at 475 K. The above results show that the wavelength composition of the luminescence is tunable by changing the symmetry of the environment in which the doped ions are located. It applies to single hosts for the regulation of white light emission.     

The temperature dependence of luminescence from a long-lasting phosphor exposed to ionizing radiation

The temperature dependence of luminescence from a long-lasting phosphor (LLP), SrAl₂O₄ : Eu²⁺,Dy³⁺, exposed to ionizing radiation has been measured to understand the LLP luminescence mechanism. Evaluation of the decay constants of the LLP exposed to -, β- or γ-rays at temperatures from 200 to 390 K showed that the decay constant is divided into four components ranging from 10⁻⁴ to 10⁻¹ s⁻¹ with activation energies of 0.02–0.35 eV.

Total luminous intensity from the LLP with changing irradiation temperature has its maximum value around the room temperature. Irradiation at elevated temperature (390 K) has the total luminescence pattern with monotonous decrease as temperature rises. As a result of evaluating the temperature dependence of luminescence, the luminescence mechanism is considered as follows:

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硼酸使掺铁铝酸锂发光增强的现象

在硼酸存在下合成了掺铁铝酸锂荧光体,研究了在不同温度下硼酸加入量对荧光体发光强度的影响,并通过X射线粉末衍射和粒度分析,初步探讨了发光增加的原因。     

YAG：Ce Phosphors for WLED via Nano-Pesudoboehmite Sol-Gel Route

The sub-micron sized YAG ： Ce phosphors were synthesized via a modified sol-gel method by peptizing nano-pesudoboehmite particulate. It is found that YAG phase from the dried gel powders appears at 1000 ℃ then the pure YAG phase exists at a relatively lower sintering temperature of 1400 ℃. The smaller sizes of phosphors in the ranges of 1 - 3 μm are obtained due to the contribution of seeding effects of nano-sized alumina particles to strengthen each step of the processes. Both the excitation and emission spectra of photoluminescence of the phosphor obtained at 1400 ℃ meet well with the spectroscopic requirements of the WLED phosphors.     

Luminescence Characterization of Mg Doped Y2O2S:Ti Long Afterglow Phosphor

Y1.94-xMgxO2S:0.06Ti (0≤x≤0.10) phosphors with long afterglow were synthesized by solid state reaction route. The photoluminescence spectra, decay curves, thermoluminescent spectra and chromaticity coordinate curves were investigated. The results show that the luminescence intensity of Y1.94-xMgxO2S:0.06Ti (0≤x≤0.10) phosphors decrease gradually with increasing Mg2 ion content, and the shape of luminescence spectra and chromaticity coordinate change as well. Furthermore, two thermoluminescent peaks in single Ti-doped Y2O2S sample are found at 91.8 and 221.5 ℃, respectively. Nevertheless, significant different spectra were found for the Mg, Ti co-doped Y2O2S samples that three thermoluminescence peaks appear at 52.3, 141.7 and 226.8 ℃, respectively. These results indicate that the co-doped Mg ion changes the inherent trap depth of single Ti-doped Y2O2S:Ti phosphor, and induces simultaneously a new trap level in the Y1.94-xMgxO2S:0.06Ti phosphor. Based on the analysis of thermoluminescent spectra, photoluminescent spectra, decay curve and crystal structure defect, it was proposed that the varied structure defect and introduced new trap level by the doped Mg2 ions should be responsible for reducing luminescence intensity and varying color in the Y1.94-xMgxO2S:0.06Ti phosphor.     

壳聚糖对水中磷的吸附处理研究

采用天然高分子聚合物壳聚糖对含磷废水进行吸附处理，考察了壳聚糖前处理的方式、处理时间、pH值、壳聚糖用量等条件对吸附率的影响，得出壳聚糖前处理最佳pH值为2．0；处理的水样pH值为6．0—6．2时，吸附磷的效果最好；最佳处理时间为40—50min，吸附率达到74．14％，吸附量为0．342mg／g。动态解吸，回收率可达91．84％。壳聚糖还可以进行再生，再生利用率为94．34％，同时还探讨了该方法在实际中的具体应用。     

A new oxyapatite red phosphor Eu3+-doped Ca3Y7(BO4)(SiO4)5O: Synthesis,structure and luminescence properties

A series of new oxyapatite red phosphors Ca₃Y₇(BO₄)(SiO₄)₅O doped with different concentrations of Eu³⁺ were successfully synthesized by high temperature solid state method. The X-ray diffraction (XRD) Rietveld refinement results show that the structure of the phosphor belongs to space group P6₃/m and Eu³⁺ ion replaces Y³⁺ ion. The emission spectrum consists of the characteristic emission peaks corresponding to Eu³⁺ under the excitation of 274 nm and the dominant emission peak is at 614 nm (⁵D₀→⁷F₂ of Eu³⁺). The concentration quenching effect occurs and the optimized Eu³⁺ concentration is 4.0 mol%. The energy level diagram for luminous mechanism is also given and the non-radiative energy transfer mechanism between Eu³⁺ is mainly exchange interaction. The CIE coordinate is close to the ideal red light and the color purity is higher than 99.79%. Moreover, the phosphor exhibits moderate thermal stability because the photoluminescence intensity at 423 K is still maintained at higher than 78.97% of that at room temperature. The internal quantum efficiency of Ca₃Y₇(BO₄)(SiO₄)₅O:4.0 mol%Eu³⁺ phosphor is 58.2%. A red light emitting diode (LED) device based on it can emit bright red light. The CCT values of the device are basically unchanged when driven by various bias current. The results show that Ca₃Y₇(BO₄)(SiO₄)₅O:Eu³⁺ is a new type of oxyapatite red fluorescent material with good comprehensive performances.     

不同添加剂对SrAl2O4:(Eu,Dy)磷光体发光性能的影响

在较低的温度下用燃烧合成法快速合成了 Eu2 ,Dy3 掺杂的SrAl2O4长余辉磷光体发光材料.研究了P2O5,CaF2,H3BO3,NaF 几种添加剂对SrAl2O4:(Eu,Dy)粉体发光性能的影响.结果发现:H3BO3和P2O5的添加有利于改善磷光体的发光性能,而在配料中加入CaF2和NaF,磷光体发光效率降低.随着这几种添加剂的加入,SrAl2O4:(Eu,Dy)磷光体材料发射光谱的主发射峰不同程度的出现蓝移.根据实验结果分析了添加剂的作用机理.     

无磷条件下膜生物反应器处理化工废水

在进水不含磷条件下,对膜生物反应器(MBR)系统的运行情况进行了研究。结果表明:微生物充分利用体内储存的聚磷酸盐及死亡细胞和碎片中的磷进行生长,因此混合液悬浮固体(MLSS)仍能增加,最后稳定在8.5 g/L;化学需氧量(COD)处理效果一直较好;氨氮和总氮去除率可达90％及70％;系统经历了丝状菌膨胀和非丝状菌膨胀两个阶段。在缺磷的情况下,MBR系统的处理结果并未受到很大影响。     

Synthesis and luminescence properties of red phosphor CaO: Eu3+

Ca(NO₃)₂·4H₂O, Eu(NO₃)₃ and H₂C₂O₄·2H₂O were adopted to synthesize CaO: Eu³⁺ with the chemical co-precipitation method, and the effects of the calcination temperature and Eu³⁺ doping concentration on the phosphor structure and its luminescent properties were investigated by TG-SDTA, XRD, and PL-PLE. The results confirm that the Eu³⁺ ions as luminescent centers substitutes Ca²⁺ sites without changing the crystal structure of cubic CaO. The optimum calcination temperature and the optimum concentration of Eu³⁺ are 1 100 ° and 1 mol%, respectively, under which the best crystallinity and highest PL intensity appeared. The maximum emission wavelength is 592 nm (⁵D₀→⁷F₁) which is excited by xenon lamp with the wavelength of 200–280 nm, indicating that the Eu³⁺ ion mainly locates in the symmetric position (O_h) in the crystal lattice of CaO. Funded by the Science and Technology Bureau of Sichun Province(No. 2006J13-059) and Education Bureau of Sichun Province (No. 2006A094)