Tm3+/Yb3+共掺碲酸盐玻璃的近红外发光及能量传递机理

采用高温熔融法制备了组分为TeO₂-ZnO-Na₂O的Tm³⁺离子单掺和Tm³⁺/Yb³⁺共掺碲酸盐玻璃,应用Judd-Ofelt理论计算分析了玻璃样品的强度参量Ω_t(t=2, 4, 6),自发辐射跃迁几率A,荧光分支比β和荧光辐射寿命τ_rad等光谱参量,测量得到了不同Yb³⁺离子掺杂浓度下玻璃样品的Tm³⁺离子上转换发光谱.结果显示,在980 nm泵浦光激励下玻璃样品发射出强烈的近红外上转换荧光.对Tm³⁺离子上转换发光分析表明,强烈的Tm³⁺离子近红外上转换发光主要来自于Yb³⁺/Yb³⁺离子间的共振能量传递以及基于单声子和双声子辅助的Yb³⁺/Tm³⁺离子间的非共振能量传递过程,并进一步计算得到了声子贡献比和能量传递系数.最后,计算分析了Tm³⁺:³F₄→³H₆能级间跃迁的1.8 μm波段吸收截面、受激发射截面和增益系数.研究表明,Yb³⁺/Tm³⁺共掺TeO₂-ZnO-Na₂O玻璃可以作为近红外波段固体激光器的潜在增益基质.     

PbWO4闪烁晶体的辐照损伤机理研究

完成了640—1040℃温度范围内钨酸铅［PbWO₄(PWO)］晶体的退火实验,观察到较低温退火时晶体中本征色心吸收带(350nm)先是增加,其后随退火温度的升高而逐渐降低直至消除的全过程．分析了PWO晶体的本征缺陷和电荷补偿机制．讨论了退火过程中氧进入晶体后色心的产生和转化规律,并提出可能发生Pb³⁺→Pb⁴⁺的进一步氧化过程,从而导致Pb³⁺空穴中心的湮没．测量并比较了不同退火温度处理后PWO晶体的紫外辐照诱导色心     

Ce3+ 掺杂高密度氧化物玻璃的闪烁性能研究

用高温熔融法制备了以SiO₂-B₂O₃-Al₂O₃-Gd₂O₃为基质系统Ce³⁺掺杂的玻璃样品, 测试样品的密度、紫外——可见透射光谱、紫外激发光谱和主要的闪烁性能, 并且把一部分闪烁性能和PbWO晶体及BGO晶体做比较. 着重研究了不同Ce³⁺掺杂浓度与Gd³⁺ 离子的含量对玻璃样品闪烁性能的影响规律. 结果表明: 玻璃样品具有较大的密度; 样品的X射线激发发射光谱发射峰位置都在390 nm左右, 当Ce³⁺ 离子的掺杂浓度为1.0 mol%(摩尔分数)、Gd₂O₃含量为15 mol%时, 玻璃样品的发光峰强度达到BGO晶体发光强度的90%; 同样验证了Ce³⁺ 离子具有浓度猝灭效应; Gd³⁺可以敏化Ce³⁺离子发光, 但是Gd³⁺离子到达一定浓度时, 反而会产生猝灭效应, 降低了Ce³⁺ 离子的发光. Ce³⁺ 离子掺杂SiO₂-B₂O₃-Al₂O₃-Gd₂O₃系统的闪烁玻璃有望替代闪烁晶体广泛应用于高能物理中.     

焙烧温度对SiO2负载的Co3O4纳米粒子表面氧缺陷浓度和CO氧化催化性能的影响

以传统的浸渍法,在不同焙烧温度下制备了用于CO氧化反应的Co₃O₄/SiO₂催化剂．通过激光拉曼光谱(Raman)、X射线光电子能谱(XPS)、X射线衍射(XRD)、程序升温还原(TPR)和X射线吸收精细结构谱(XAFS)表征了该系列催化剂的结构．在所有的催化剂中,XRD和Raman光谱都只检测到了Co₃O₄晶相的存在．与Co₃O₄体相相比,XPS结果表明在200 oC焙烧的(Co₃O₄(200)/SiO₂)催化剂中Co₃O₄表面上存在着过量的Co²⁺．与XPS的结果一致,TPR结果表明Co₃O₄(200)/SiO₂催化剂中Co₃O₄表面上存在氧缺陷, 并且XAFS结果也表明Co₃O₄(200)/SiO₂催化剂中Co₃O₄具有更多的Co²⁺．提高焙烧温度使得过量的Co²⁺进一步氧化为Co³⁺,同时降低了表面氧缺陷浓度,从而得到计量比的Co₃O₄4/SiO₂催化剂．在所有的负载催化剂中Co₃O₄(200)/SiO₂催化剂表现出了最好的CO氧化催化性能,表明过量Co²⁺和表面氧缺陷的存在能够促进Co₃O₄催化CO氧化反应的活性.     

Er3+单掺及Er3+/Yb3+共掺SiO2-Al2O3-La2O3玻璃光谱性质研究

研究了单掺Er³⁺及Er³⁺/Yb³⁺共掺SiO₂-Al₂O₃-La₂O₃玻璃的光谱性质随稀土离子浓度变化规律,应用McCumber理论计算了玻璃在1.53 μm的发射截面及积分吸收截面.结果表明:在Er³⁺离子掺杂浓度相同时,玻璃在980 nm吸收截面与Yb³⁺掺杂浓度成反比;当样品中Yb³⁺离子掺杂浓度为3.94×10²⁰ cm^-3时,玻璃在1.53 μm的吸收截面和发射截面最大,在1.40～1.60 μm积分吸收截面也最大;Er³⁺/Yb³⁺共掺SiO₂-Al₂O₃-La₂O₃玻璃在1.53 μm的荧光半高宽随Er³⁺掺杂浓度升高而增加,当Er³⁺离子掺杂浓度为2.41×10²⁰ cm^-3时,玻璃的荧光半高宽(FWHM)达到52.5 nm.     

Er3+及Er3+/Yb3+掺杂ZrO2-Al2O3的制备及发光性质

采用共沉淀法制备了纳米晶ZrO₂-Al₂O₃∶Er³⁺发光粉体.所制备的粉体室温下具有Er3+离子特征荧光发射,主发射在绿光,其中位于547 nm、560 nm的绿光最强,并得出稀土离子与基质之间有能量传递.对不同煅烧温度下的样品研究表明:因不同温度下所制得的样品晶相不同.研究了纳米晶ZrO2-Al2O3∶Er3+及ZrO₂-Al₂O₃∶Er³⁺/Yb³⁺的上转换发光,并分析了上转换的跃迁机制.发现ZrO₂-Al₂O₃∶Er³⁺的绿光为双光子过程,而ZrO₂-Al₂O₃∶Er³⁺、Yb³⁺的上转换光谱中,红光和绿光也为双光子过程,而极弱的蓝光为三光子过程.讨论了Er³⁺的浓度猝灭现象.最适宜掺杂浓度的原子分数为2%（Er³⁺/Zr⁴⁺）.     

Er3+/Ce3+共掺碲铋酸盐玻璃的制备及光谱特性提高研究

采用高温熔融退火法制备了系列 80TeO₂-10Bi₂O₃-10TiO₂-0.5Er₂O₃-xCe₂O₃ (x=0,0.25, 0.5,0.75,1.0 mol%)和(80-y) TeO₂-10Bi₂O₃-10TiO₂-yWO₃-0.5Er₂O₃-0.75Ce₂O₃ (y=3,6,9,12 mol%)的碲铋酸盐玻璃.测试了玻璃样品400-1700 nm范围内的吸收光谱, 975 nm抽运下的上转换发光谱和1.53 μm波段荧光谱, 以及808 nm激励下的Er³⁺离子荧光寿命和无掺杂玻璃样品的Raman光谱, 并结合Judd-Ofelt理论和McCumber理论计算了Er³⁺离子光谱参数.结果表明, 在掺Er³⁺碲铋酸盐玻璃中引入Ce³⁺离子进行Er³⁺/Ce³⁺共掺, 通过Er³⁺离子⁴I_11/2能级与Ce³⁺离子²F_5/2 能级间基于声子辅助的能量传递过程,可以有效抑制Er³⁺离子上转换发光并明显增强其 1.53 μm波段荧光;同时,在现有Er³⁺/Ce³⁺共掺玻璃组分基础上引入WO₃, 可进一步提高1.53 μm波段荧光并展宽其荧光发射谱. 研究结果对于获取优异光谱特性的宽带掺Er³⁺光纤放大器玻璃基质具有实际意义.     

介孔SO42-/Zr-SBA-15催化废弃油制生物柴油

采用廉价的无机锆源(无水硝酸锆)通过一步法合成表面含强Lewis酸位的SO₄^2-/Zr-SBA-15,该催化剂材料在废弃食用油和甲醇酯交换制生物柴油过程中表现出良好的催化活性和选择性. 实验考察了酯交换反应的最佳条件为：反应温度160 oC、反应时间12 h、催化剂Zr:Si为0.11、催化剂用量为10%、醇油比30:1. SO₄^2-/Zr-SBA-15在最佳反应条件下可使甘油三酯的转化率达到92.3%,脂肪酸甲酯的产率为91.7%. SO₄^2-/Zr-SBA-15具有高比表面积的介孔结构和表面酸性,且具有良好的反应稳定性和重复性,反应7次后的脂肪酸甲酯的产率仍稳定保持在74 ±1%.     

高温注氦及随后230MeV的208Pb27+辐照Al2O3的光致发光谱的研究

主要研究了110keV的He⁺高温注入Al₂O₃单晶及1.1MeV/u的²⁰⁸Pb²⁷⁺辐照注氦Al₂O₃样品的光致发光的特性. 从测试结果可以清楚地看到在375nm, 413nm和450nm处出现了强烈的发光峰. 并且在600K, 5×10sup>16ions/cm²剂量点, 样品的发光峰是最强的. 这 表明He⁺注入Al₂O₃后使带隙中深的辐射中心复合的效率大幅度提高, 极大的增强了其发光强度,而且发光伴随着蓝移现象. 而经过高能²⁰⁸Pb²⁷⁺辐照后的样品, 在390nm出现了新的发光峰,从FTIR谱中我们能够看到, 可能是²⁰⁸Pb²⁷⁺辐照相对沉积膜出现一定的晶化, 其中含有许多纳米尺寸的Al₂O₃晶粒所致.     

Er3+/Ce3+共掺TeO2-Bi2O3-TiO2玻璃的热稳定性和光谱特性研究

用高温熔融法制备了Er³⁺/Ce³⁺共掺新型碲酸盐玻璃(TeO₂-Bi₂O₃-TiO₂).采用差热分析方法研究了玻璃的热稳定性,测试并分析了不同Ce³⁺离子掺杂浓度下Er³⁺离子的吸收光谱、上转换光谱和荧光光谱特性.研究结果表明,制备的碲酸盐玻璃具有很好的热稳定性,玻璃析晶温度Tx与玻璃转变温度Tg之差(ΔT=Tx-Tg)达到了185 ℃,高于其它文献的报道|同时,Ce3+离子共掺引入的能量转移(Ce³⁺∶2F5/2+Er³⁺∶4I11/2→Ce³⁺∶2F7/2+Er³⁺∶4I13/2)有效地抑制了Er³⁺离子上转换发光并显著增强了1.53 μm波段荧光强度,而发射截面随着Ce³⁺离子掺杂浓度相应增大.优异的热稳定性以及光谱性能揭示Er³⁺/Ce³⁺共掺碲酸盐玻璃是一种潜在的制备宽带掺铒光纤放大器的理想增益介质.     

Angular dependence of the207Pb NMR linewidth in Pb(NO3)2 due to14N—207Pb direct dipole-dipole interaction

NMR signals of²⁰⁷Pb²⁺ have been measured in a single crystal of Pb(NO₃)₂. For rotation axes perpendicular to the static magnetic field and perpendicular to the (100) or (011) plane the linewidths of these signals vary by a factor 2 for different rotation angles of the single crystal. This dependence of the linewidth on the orientation has been explained by a¹⁴N —²⁰⁷Pb direct dipole-dipole coupling and it has been used to assign the different Pb²⁺ NMR signals to the different Pb²⁺ sites in the cubic unit cell of Pb(NO₃)₂.     

三维金属有机骨架/石墨烯水凝胶均相降解纤维素为小分子酸的研究

通过在三维还原氧化石墨烯孔径中原位生长ZIF-8纳米粒子,制备了三维金属有机骨架/石墨烯催化剂.这种ZIF-8/rGO纳米复合材料同时具有介孔和微孔,并且拥有高比表面积和大量催化位点,是生物质转化的理想催化剂.将纤维素溶解于氢氧化钠水溶液中,在水热条件下,使用这种催化剂,纤维素可以被充分降解转化.纤维素转化率可以达到100%,其主要产物是甲酸,产率最高可达93.66%.催化剂还可以被回收,重复使用依然具有很好的催化效果.     

ELECTRONIC STRUCTURE OF THE T*-TYPE SUPERCONDUCTORS (Bi0.5Sr1.5)(Y, Ce)2Cu2Oy STUDIED BY PHOTOELECTRON SPECTROSCOPY

The electronic structure of T^*-type compounds (Bi_0.5Sr_1.5)(Y_2-xCe_x)Cu₂O_y has been studied by X-ray photoelectron spectroscopy. From analysis of the results, it was found that cation deficiency in Ce⁴⁺ introduced holes to conduction planes in the T^* phase as in the p-type infinite layer compounds. Some Cu ions in the sample without cation-deficiency contained two-oxygen coordination, which resulted in the incompleteness of the CuO₂ sheets. Bi ions in the T^* phase cuprates take exact valence of 3_{+, Pb ions cannot replace them due to the too large an ionic radius of Pb²⁺/Pb⁴⁺.}     

A novel blue-emitting phosphor: BaAl2B2O7: Pb

Pb²⁺ doped BaAl₂B₂O₇ materials were prepared by a solution combustion synthesis. The phase of the synthesized materials was determined using the powder X-ray diffraction. The photoluminescent properties of Pb²⁺ doped BaAl₂B₂O₇ materials were investigated using spectrofluorometer at room temperature. The emission and excitation bands of BaAl₂B₂O₇: Pb²⁺ were observed at 423 and 266 nm, respectively. The dependence of the emission intensity on the Pb²⁺ concentration for BaAl₂B₂O₇: Pb²⁺ was investigated. The Stokes shifts of BaAl₂B₂O₇: Pb²⁺ was calculated to be 13 953 cm⁻¹.     

Ultrasonic-assisted synthesis of polyacrylamide/bentonite hydrogel nanocomposite for the sequestration of lead and cadmium from aqueous phase: Equilibrium,kinetics and thermodynamic studies

Clay-hydrogel nanocomposites are suitable material for mitigating the pollution/environmental impact because of their high adsorption capacity. In this study, the synthesis of polyacrylamide/bentonite hydrogel nanocomposite was assisted by ultrasound through successful incorporation of nanobentonite as filler and cross-linker into polyacrylamide framework. The adsorbent was characterized by FTIR, XRD, BET, SEM-EDX, and TEM in order to observe structural changes and sorption interactions. The effect of adsorbent dose, contact time, initial metal ion concentration and pH on the sequestration of Pb²⁺ and Cd²⁺ was analyzed. The adsorbent removed more than 95% Pb²⁺ and Cd²⁺ within first 20 min, which corresponds to relatively high pseudo-first order rate constant, k₁ (0.240 for Pb²⁺ and 0.253 1/min for Cd²⁺) and pseudo-second order rate constant, k₂ (0.031 for Pb²⁺ and 0.033 g/mg/min for Cd²⁺). The isotherm and kinetics modeling data were best described by Freundlich isotherm over the entire concentration range and pseudo-second order rate equation, respectively. The thermodynamic studies implied spontaneous and endothermic nature of adsorption process. The maximum adsorption capacity (138.33 for Pb²⁺ and 200.41 mg/g for Cd²⁺) determined using Langmuir model along with a good regeneration potential depicts that polyacrylamide/bentonite hydrogel nanocomposite could be used effectively for Pb²⁺ and Cd²⁺ uptake from aqueous solution.     

Determination of Trace Bismuth by a Solid Substrate Room Temperature Phosphorescence Quenching Method Based on Anionic Polymeric Acryclic Acid Lead Particles Containing Luminescent Eosine Molecules

Abstract

Luminescent particles of Anionic Polymeric Acryclic Acid Lead (Pb(PAA)₂) which containing eosine(HFInBr₄), Eosine nanomicroball of anionic polypropylene acid lead contained luminophores (short for E.N.PAA.L.C.L), were synthesized by a sol‐gel method, using anionic polymeric acryclic acid sodium (PAANa) as the precursor and Pb²⁺ as the precipitant. NH₄Ac‐HAc can react with the Pb²⁺ in E.N.PAA.L.C.L, causing it to decompose into aqueous soluble components. E.N.PAA.L.C.L‐ NH₄Ac‐HAc can emit strong and stable solid substrate room temperature phosphorescence (SS‐RTP) on filter paper, and bismuth, mercury or iodine can cause a decrease in phosphorescence intensity. Based on the facts above, a new method for the determination of trace bismuth by an SS‐RTP quenching method was established. The linear range of this method was 0.01–0.20(pg spot^?1) (4.0×10^?12 g ml^?1) of Bi³⁺, with a detection limit (LD) of 0.0016 pg spot^?1, and the regression equation of the working curve was ΔIp=61.01+237.8 m_Bi3+ (pg spot^?1), r=0.9992. This method was applied to the determination of trace bismuth in human hair and well water samples with satisfactory results. The mechanism of SS‐RTP emission was also discussed.     

Removal of heavy metals from aqueous solutions using Fe3O4, ZnO, and CuO nanoparticles

This study investigated the removal of Cd²⁺, Cu²⁺, Ni²⁺, and Pb²⁺ from aqueous solutions with novel nanoparticle sorbents (Fe₃O₄, ZnO, and CuO) using a range of experimental approaches, including, pH, competing ions, sorbent masses, contact time, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The images showed that Fe₃O₄, ZnO, and CuO particles had mean diameters of about 50?nm (spheroid), 25?nm (rod shape), and 75?nm (spheroid), respectively. Tests were performed under batch conditions to determine the adsorption rate and uptake at equilibrium from single and multiple component solutions. The maximum uptake values (sum of four metals) in multiple component solutions were 360.6, 114.5, and 73.0?mg?g^?1, for ZnO, CuO, and Fe₃O₄, respectively. Based on the average metal removal by the three nanoparticles, the following order was determined for single component solutions: Cd²⁺?>?Pb²⁺?>?Cu²⁺?>?Ni²⁺, while the following order was determined in multiple component solutions: Pb²⁺?>?Cu²⁺?>?Cd²⁺?>?Ni²⁺. Sorption equilibrium isotherms could be described using the Freundlich model in some cases, whereas other isotherms did not follow this model. Furthermore, a pseudo-second order kinetic model was found to correctly describe the experimental data for all nanoparticles. Scanning electron microscopy, energy dispersive X-ray before and after metal sorption, and soil solution saturation indices showed that the main mechanism of sorption for Cd²⁺ and Pb²⁺ was adsorption, whereas both Cu²⁺ and Ni²⁺ sorption were due to adsorption and precipitation. These nanoparticles have potential for use as efficient sorbents for the removal of heavy metals from aqueous solutions and ZnO nanoparticles were identified as the most promising sorbent due to their high metal uptake.     

Luminescence characteristics of Pb centres in undoped and Ce-doped Lu3Al5O12 single-crystalline films and Pb→Ce energy transfer processes

At 4.2-350 K, the steady-state and time-resolved emission and excitation spectra and luminescence decay kinetics were studied under excitation in the 2.5-15 eV energy range for the undoped and Ce³⁺-doped Lu₃Al₅O₁₂ (LuAG) single-crystalline films grown by liquid phase epitaxy method from the PbO-based flux. The spectral bands arising from the single Pb²⁺-based centres were identified. The processes of energy transfer from the host lattice to Pb²⁺ and Ce³⁺ ions and from Pb²⁺ to Ce³⁺ ions were investigated. Competition between Pb²⁺ and Ce³⁺ ions in the processes of energy transfer from the LuAG crystal lattice was evidenced especially in the exciton absorption region. Due to overlap of the 3.61 eV emission band of Pb²⁺ centres with the 3.6 eV absorption band of Ce³⁺ centres, an effective nonradiative energy transfer from Pb²⁺ ions to Ce³⁺ ions takes place, resulting in the appearance of slower component in the luminescence decay kinetics of Ce³⁺ centres and decrease of the Ce³⁺-related luminescence intensity.     

Eu2－xPbxRu2O7中的金属-绝缘体相变和自旋玻璃态行为

通过对Eu_2-xPb_xRu₂O₇(x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0和1.8)系列样品的结构、电阻和磁化率的观测，结果发现，随着Pb替代浓度x值的增加，样品的电阻率逐渐减小，系统在x=0.8附近发生了金属-绝缘体(M-I)相变；Ru⁴⁺的局域磁矩及其自旋玻璃冻结温度T_G也随之降低. 在该体系中，Pb²⁺对Eu³⁺的部分替代使样品中载流子浓度增加，Pb的6p能带与Ru 4d电子的T_2g能带混合，能带得以拓宽，Ru 4d电子的巡游性增强，导致该体系物性的系列变化. 关键词： 自旋几何受挫 2-xPb_xRu₂O₇体系')" href="#">Eu_2-xPb_xRu₂O₇体系 金属-绝缘体相变 自旋玻璃态     

Nuclear magnetic shielding tensors of207Pb2+ in Pb(NO3)2

The NMR signals of²⁰⁷Pb were observed in a single crystal of Pb(NO₃)₂ and could be assigned to the four different Pb²⁺ sites by the dependence of the linewidths on the orientation. Four different nuclear magnetic shielding tensors with equal principal values but with different characteristic vectors could be determined. The symmetry of the shielding tensors is in agreement with the symmetry at the Pb²⁺ sites. It is shown, that intermolecular contributions can not account for the anisotropy of the nuclear magnetic shielding, which is 3 of the isotropic absolute magnetic shielding.