Long-Lasting Properties of Rare Earth-Doped Y_2O_2S Phosphors

The aim of this presentation is to report a new result of afterglow materials. The Y 2O 2S∶Ln 3+ (Ln=Sm, Tm) phosphors show bright reddish orange and orange-yellow colors when excited by UV or visible light. The main spectroscopic characterizations of Sm 3+ and Tm 3+ in yttrium oxysulfide and their long-lasting phosphorescence were measured and discussed in this presentation. Their long-lasting phosphorescence can be seen by the naked eyes clearly for about one hour in the dark room after the irradiation light sources were removed. XRD and photoluminescence (PL) spectra as well as the luminance decay were used to characterize these long-lasting phosphorescence phosphors. The results of XRD indicate that the products synthesized through the flux fusion method under 1050 ℃ for 6 h have a good crystallization without any detectable amount of impurity phase. Both the PL spectra and luminance decay results reveal that these phosphors have efficient luminescent and good long-lasting properties. We believe that the experimental data gathered in our present work will be useful in finding some new long-lasting phosphors with different colors.

Flux and concentration effect on Eu^(3+) doped Gd_2(MoO_4)_3 phosphor

A novel red emitting phosphor Gd2（MoO4）3：Eu^3＋ was prepared by solid reaction, using Gd2O3, Eu2O3 and WO3 as starting matedals and NH4F as flux. The effects of flux content and Eu^3＋ concentration on the crystal structure, morphology and luminescent properties were investigated using XRD, SEM and fluorescent spectrum measurement. The XRD patterns showed that the resultants had the monoclinic structure. With the increase in flux amount, their crystallization significantly improved. The SEM images indicated that the mean size of the phosphor particles was around 2 μm, and agglomeration of the phosphor particles appeared while introducing higher flux amount. The excitation spectra exhibited more intense f-f transitions originating from ground state 7^F0 to upper states 5^L6 and 5^D2 than the charge transfer band. The concentration quenching of Eu^3＋ emission indicated that energy transfer from Eu^3＋ to molybdate host existed even at lower Eu^3＋ concentration.

Y_2O_2S∶Eu,Mg,Ti,Tb红色长时发光材料的研究

利用高温固相反应法合成了一种新型的红色长时发光材料———Y2O2S∶Eu,Mg,Ti,Tb。材料的XRD测试结果表明Eu掺杂引起Y2O2S∶Eu,Mg,Ti,Tb晶胞增大。激发光谱、发射光谱和发光衰减曲线表明该材料是一种适合紫外线和可见光激发,并具有很好的长时发光性能的红色长时发光材料。热释光谱测试结果表明该材料可能具有两个较深的陷阱能级。研究了Eu,Mg,Ti,Tb的加入量对材料发光特性的影响,结果表明:Eu,Mg,Ti,Tb影响材料的初始亮度和发光时间,Eu决定材料的红色比。

乳状液膜法制备硫氧化物超细X射线发光粉

采用乳状液膜法制备了颗粒均匀的Gd-Tb草酸盐微粒,将草酸盐粒子放在硫气气氛下焙烧后得到Gd2O2S∶Tb超细X射线发光粉。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、红外(IR)光谱、光致发光(PL)光谱和X射线激发发光光谱(XEL)对微晶进行了表征。结果表明,900℃下焙烧后的粒子显示了单一的六角形Gd2O2S晶相,与传统固相法相比,有效降低了焙烧温度。根据谢乐公式,估算一次粒径为29nm,初级粒子尺寸较小,这在一定程度上可以提高成像系统的空间分辨率。从SEM照片来看,粒子显示了一定的团聚性,但团聚尺寸<5μm,为超细X射线发光粉。同时,在254nm紫外光和X射线激发下,Gd2O2S∶Tb发光粉都显示出Tb3+的特征发射峰,并且通过分析红外光谱对样品发光性能的影响作了详细的讨论。

稀土硫氧化物发光材料的制备技术

稀土硫氧化物是一类重要的发光体基质材料,有着广阔的应用前景。主要介绍了国内外制备稀土硫氧化物材料的常用方法,如固相反应法、固-气反应法、醇溶液热合成法和微波辐射法,并对各种方法的优缺点进行了评述。在此基础上,还对处于研究前沿的稀土硫氧化物纳米材料制备技术进行了详细的介绍,并分析了先驱物硫化法和氧化物硫化法各自的特点。最后展望了该类材料制备技术的发展趋势。

纳米Y_2O_2S∶Tb X射线发光粉的合成及发光性质

以EDTA为螯合剂、尿素为沉淀剂,采用络合沉淀法制备了Y2O2S:Tb纳米X射线发光粉.通过X射线衍射(XRD)、光致发光(PL)光谱和X射线激发发光(XEL)光谱对纳米发光粉进行了表征,并研究了纳米晶的发光性能及Tb3+离子的能量传递过程.研究表明:所制备样品显示了单一的六角结构,其一次粒径约为32nm.在254nm紫外光和X射线激发下,Y2O2S:Tb X射线发光粉都显示了Tb3+离子的特征发射峰,分别起源于5D3和5D4能级到基态能级的跃迁.

Preparation and characterization of monodisperse spherical particles of X-ray nano-phosphors based on Gd_2O_2S:Tb

Monodisperse spherical Gd2O2S:Tb nanoparticles have been prepared using an improved homogeneous precipitation method combined with solid-gas sulfuration technology. The effects of Tb3+-doped concentration on luminescent intensity and color purity of samples were investigated, and the optimal Tb3+-doped concentration was determined. Under the excitation of X-ray, the obtained sample shows excellent luminescent properties, and its luminescent intensity is increased by about 50% under lower sulfuration temperature compared with that of the Gd2O2S:Tb nanoparticles prepared by complex precipitation method.

Redox behavior of gold supported on ceria and ceria-zirconia based catalysts

A series of gold-based catalysts were prepared by deposition precipitation or incipient wetness impregnation on CexZ1-xO2 solid solutions （0.28≤x≤1.00）. The morphological and structural characterization of these catalysts were carried out with X-ray diffraction, trans- mission electron microscopy （TEM） analysis and physical adsorption technique, and their redox properties were studied by temperature programmed reduction using both H2 and CO as probe molecules. Two cycles of oxidation/reduction were carried out in order to evaluate the effects of redox aging and gold sintering on the oxygen exchange capability. As observed with other noble metals, gold enhanced and promoted the ceria reduction at lower temperatures. Reduction by CO was shown to be dependent on the fine dispersion of gold and to be nega- tively affected by the ageing process more than reduction with hydrogen. This might have implications in reactions like water gas shift and CO-PROX which involve CO as a main reactant.

Characterization of Superfine Sr_2CeO_4 Powder Prepared by Microemulsion-Heating Method

Powder phosphor of Sr2CeO4 is prepared by microemulsion-heating method and a film of the phosphor on ITO glass is formed by electrophoretic deposition. Field emission scanning electron microscopy （FE-SEM） images show that the powder fired at 850 ℃ for 4 h has a spherical shape with an average diameter of 70 - 80 nm whereas the powder sintered at 900 ℃ for 4 h and 1000 ℃ for 4 h have shuttle-like and spherical shapes, respectively, with both sizes less than 1μm. X-ray diffraction （XRD） pattems indicate that the superfine Sr2CeO4 exhibits an orthorhombic crystal structure. Roomtemperature photoluminescence （PL） measurements show that there are three excitation peaks located at around 262, 280 and 341 nm, and all the Sr2CeO4 samples display an intense blue emission at 470 nm with CIE coordinate of （x, y） = （0.176, 0.283）. The quantum yield of phosphor is high up to 0.47 ±0.04. Compared with Sr2CeO4 samples prepared with traditional high-temperature heating, the phosphor synthesized with this method has a smaller size, lower calcination temperature, and shorter calcination time, and the main excitation and emission bands are blue shifted about 30 and 12 tun respectively. The startup voltage for Sr2CeO4 film on ITO glass shifts from 2700 to 4000 V with increasing thickness of the film.

Luminescence property of Eu-doped fluorochlorozirconate glass-ceramics

A series of Eu2＋-doped fluorochlorozirconate glass-ceramics were prepared by solid state reaction method. X-ray diffraction, pho- toluminescence, photo-stimulated luminescence （PSL） and the turbidity of fluorozirconate glass containing BaCl2 nano- and micro-crystals were measured for the samples annealed at 290℃ for 10 rain The PSL was attributed to the characteristic emission of Eu2＋ in nano-crystallites of BaCI2, which formed in the glass upon annealing. The PSL efficiency of the glass ceramic was increased by increasing the concentration of BaCl2, which, however, resulted in the decreasing in the transparency of the sample. The sample turned to a semi-transparent glass ceramic or even an opaque and milky white one from a near-transparent glass. The trade-off between optical transparency and PSL intensity over different concentrations of BaCl2 for X-ray imaging plate applications was briefly discussed.

Photoluminescence properties of YAG:Ce3+,pr3+nano-sized phosphors synthesized by a modified co-precipitation method

Abstract： Monophasic Ce3＋ and Pr3＋ co-doped yttrium aluminum garnet （YAG：Ce3＋,pr3＋） nanoparticles with good dispersity and uniform grain sizes in the range of 50-80 nm were prepared by a two-step route, which consisted of a modified co-precipitation preparation of mixed metal hydroxide hydrate intermediates at low temperature of about 40℃ and a subsequent calcination conversion of the synthesized intermediates to crystalline nanoparticle products at about 1000℃. The influences of both the lanthanide ion （Ce3＋ and Pr3＋） doping concentration and different doping （Ce3＋/pr3＋） ratio on the photoluminescence intensity were systematically investigated. The synthesized （Ce0.6Pr0.4）0.04Y2.96Al5O12 nanoparticles were near spherical nanoclusters with good dispersity and uniform sizes in the range of 50-80 nm for about 85% of the particles. The strongest photoluminescence intensity was observed for the （Ce0.6Pr0.4）0.04Y2.96Al5O12 nanoparticle products.

X-ray-activated UVA long persistent luminescence from defective fluoride elpasolites

Long persistent phosphors have received significant attention owing to their attractive photophysical properties.Here,we report a new long persistent phosphor exhibiting strong ultraviolet A(UVA)afterglow.The phosphors were synthesized by a solid-state reaction method.We find that the obtained phosphors demonstrate super long UVA-afterglow emissions after irradiation by X-ray source,and the afterglow can last more than 50 h.A wide range of experimental characterizations indicate that the Tb^3+doped fluoride elpasolite phosphors are defective and some fluoride ions are replaced by oxygen ions,which creates electron traps with suitable trap depths.Our results establish that Tb^3+can act as optical emitters in wide-bandgap hosts that can result in the UVA afterglow.This work enriches the bank of UV long persistent phosphors,and may stimulate more efforts for the design and synthesis of this kind of optical materials.

Synthesis and characterization of Ca0.9Mg0.1TiO3：Pr3＋,Ag＋ phosphor

Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ phosphors were synthesized by solid-state reaction technique. The crystalline phase and luminescence performances of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ were observed by X-ray powder diffractometer（XRD）, transmission electron microscope（TEM）, photoluminescence spectrometer and brightness meter, respectively. The addition of Ag~＋ can diminish in the crystal particle sizes of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）. Because Ag＋ can reduce the concentration of the undesirable defects in the phosphor, luminescence intensity of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ is 2.3 times as high as that of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）at the same preparation condition. The effect of Ag＋ on the persistent afterglow properties is to deepen the energy storage traps and enhance the energy transfer efficiency from Ca_（0.9）Mg_（0.1）TiO_3 to Pr^（3＋）. The persistent afterglow properties of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ are better than those of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋） at the same preparation condition. In conclusion,Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ phosphor with molar ratio of Ag~＋to Pr^（3＋） 3：1 obtained at 900 ℃ for 4 h exhibits the optimal photoluminescence performances.

煅烧温度对白色长余辉发光材料Y_2O_2S:Tb^(3+),Sr^(2+),Zr^(4+)形貌及发光性能的影响

采用高温固相法合成了白色长余辉发光材料Y2O2S:Tb3+,Sr2+,Zr4+,利用X射线衍射、扫描电子显微镜、荧光分光光度计、照度计和热释光谱仪研究了煅烧温度对样品物相、形貌及发光性能的影响。结果表明:在950℃煅烧时,样品为Y2O3与Y2O2S的混合相,其中Y2O3为主相;在1000和1 050℃煅烧时为纯的Y2O2S相;当温度高于1 050℃时。再次出现Y2O3相;用288 nm波长光激发样品,Tb3+发射峰形状与位置不变,其中位于417 nm蓝光与544 nm黄绿光主发射峰归属于Tb3+的5D3→7F5与5D4→7F5跃迁;当煅烧温度为1000℃时,样品的能级陷阱深度为0.64eV,余辉时间为160s(≥1mcd/m2)。

Synthesis of high quality Ce：YAG nanopowders by graphene oxide nanosheet-assisted co-precipitation method

（Ce_（0.04）Y_（2.96））Al_5O_（12） phosphor nanoparticles were prepared by a modified co-precipitation method with graphene oxide（GO） nanosheets used as dispersing agent. The GO concentration is controlled at 0.0.005,0.01, 0.02, and 0.03 g/L. The addition of lamellar GO nanosheets in the precipitant solution possibly enhances both the dispersity of precursor particles and the crystallinity of phosphor nanoparticles. Pure Ce-doped YAG phase is obtained by calcining the precipitate at 1000 ℃ for 3 h. The（Ce_（0.04）Y_（2.96））Al_5 O_（12）phosphor nanoparticles have an average size of 64 nm and there is no significant change on particle size with increase of the GO concentration in precipitant solution. The luminescence property of（Ce_（0.04）Y_（2.96））Al_5O_（12） phosphor nanoparticles varies with different concentrations of GO. The photoluminescence emission intensity of the optimum sample with 0.02 g/L GO is about 1.6 times higher than the sample without using GO.

Spectral change and far-red emission of Mn^(2+)ions co-doped NaSrB_(5)O_(9):Dy^(3+)luminescence material for plant growth LEDs

Due to the characteristic emission of phosphors,phosphor-converted LEDs have been employed to provide the requisite light sources for indoor plant growth in the optical agricultural industry.Herein,we prepared a series of Mn^(2+)co-doped NaSrB5 O9:Dy^(3+)phosphors via a solid-state reaction method.These phosphors have significant three-band emissions at 467 nm(blue region),606 nm(orange region),and765 nm(far-red region),ascribed to the^(4)F_(9/2)-^(6)H_(15/2)and 4 F9/2-6 H13/2 transitions of the Dy^(3+)ions and the^(4)T_(1g)(G)-^(6)A_(1g)(S)spin-forbidden transition of the Mn^(2+)ions,respectively,when excited by light of 376 nm(near-UV region).The co-dopant in the host material facilitates tunable photoluminescence(PL)due to energy transfer from the Dy^(3+)ions to the Mn^(2+)ions.The three emission peaks from the prepared phosphors well match with the absorption spectra of the photosynthesis pigments of plants,chlorophyll and phytochrome,which can absorb blue(400-500 nm),orange-red(550-700 nm),and infrared(IR)radiation,indicating that these phosphors have potential applications in the fabrication of plant-growth LEDs.Prior to the PL studies,the structure of the phosphors was determined by X-ray diffraction,refined by Rietveld method and chemically quantified by X-ray photoelectron spectroscopy.