Luminescence,Plasmonic, and Magnetic Properties of Doped Semiconductor Nanocrystals

Introducing a few atoms of impurities or dopants in semiconductor nanocrystals can drastically alter the existing properties or even introduce new properties. For example, mid-gap states created by doping tremendously affect photocatalytic activities and surface controlled redox reactions, generate new emission centers, show thermometric optical switching, make FRET donors by enhancing the excited state lifetime, and also create localized surface plasmon resonance induced low energy absorption. In addition, researchers have more recently started focusing their attention on doped nanocrystals as an important and alternative material for solar energy conversion to meet the current demand for renewable energy. Moreover, the electrical and magnetic properties of the host are also strongly altered on doping. These beneficial dopant-induced changes suggest that doped nanocrystals with proper selections of dopant–host pairs may be helpful for generating designer materials for a wide range of current technological needs. How properties relate to the doping of a variety of semiconductor nanocrystals are summarized in this Review.     

A New Maleato-Bridged Mn(II) Phen Complex: Structure and Magnetic Properties of Mn(phen)(C4H2O4)

Reaction of freshly-precipitated MnCO₃, phenanthroline monohydrate and maleic acid in CH₃OH/H₂O (pH = 6.23) at 50°C afforded a new maleato bridged, catenated coordination polymer Mn(phen)(C₄H₂O₄), where the Mn atoms are each octahedrally coordinated by two N atoms of one phen ligand and four O atoms of three maleato ligands (d(Mn-N) = 2.300, 2.331 Å; d(Mn-O) = 2.112-2.207 Å). The maleato ligand chelates one Mn atom to form a seven membered ring while two carboxylate groups of different maleato ligands bridge two Mn atoms to form an eight-membered ring, 1D ¹ _∞[Mn(phen)(C₄H₂O₄)_3/3] chains being generated in a sequence of seven- and eight-membered rings. Significant interchain π-π stacking interactions are responsible for the supramolecular assembly of the polymeric ¹ _∞[Mn(phen)(C₄H₂O₄)_3/3] chains into 2D layers. At low temperatures, the title complex becomes antiferromagnetic with T _Née1 = 7 K and follows the Curie-Weiss law _χm (T + 9.82) = 4.140 cm³ mol^-1 K between 30-300 K.     

钙钛矿二维纳米材料的合成和发光研究进展

钙钛矿纳米材料的研究取得了飞速发展:一方面,合成方法不断涌现,已经可以实现从零维纳米晶、一维纳米线到二维纳米片的形貌精确控制,对其尺寸和维度依赖的光学性质认识也不断深入;另一方面,钙钛矿纳米材料的光学和光电子应用也得到了快速发展,其中,基于钙钛矿量子点的光致发光和电致发光技术最受关注。 由于钙钛矿的天然层状结构,通过配体调控很容易制备出二维纳米材料,其发光性能可以通过层数和组分进行调节,最高量子产率超过85%,且具有偏振发光特性,有望成为一类新型发光材料。 本文从制备方法、光致发光和电致发光应用等方面综述了基于钙钛矿二维纳米材料的进展,并对其未来的发展方向进行讨论。     

GdF3∶Eu3+/NaGdF4∶Eu3+纳米晶的水热合成及发光性质

采用水热法,以聚乙二醇(400)为分散剂,以NaOH和HNO3溶液调节初始溶液pH值,合成GdF3∶Eu3+和NaGdF4∶Eu3+纳米晶。XRD和SEM结果表明:在酸性溶液(pH=3,5)、中性溶液(pH=7)和碱性溶液(pH=9)中,分别获得具有正交结构的GdF3∶Eu3+纳米晶,GdF3∶Eu3+和NaGdF4∶Eu3+混合晶,六方结构NaGdF4∶Eu3+棒状微米晶。根据Scherrer公式估算pH=3和pH=5时制备纳米晶的一次性粒径分别为49和28 nm。样品的发射光谱结果表明:特征发射峰来自于5D2、5D1、5D0到7FJ跃迁。在主晶相为GdF3样品中,主发射峰来自于Eu3+的5D0→7F1的磁偶极跃迁;晶相为NaGdF4样品的主发射峰来自于Eu3+的5D0→7F2电偶极跃迁。5D0→7F1和5D0→7F2跃迁发射相对强度比值显示:Eu3+在NaGdF4晶体中的格位对称性下降。激发光谱显示出Gd3+和Eu3+具有较好的能量传递。     

棒状LaF3∶Eu3+纳米晶的制备与发光性能

采用一种简单的液相反应法在室温下合成了棒状的LaF3∶Eu3+纳米晶, 对其结构和发光性能进行了表征. XRD分析结果表明, 室温下即可得到结晶良好的六方晶相的LaF3, 灼烧之后样品的衍射峰增强, 没有杂相产生. TEM照片表明, 棒状LaF3∶Eu3+纳米材料的直径为8 nm左右, 长度达到50 nm. 荧光光谱表明, 室温下合成的棒状LaF3∶Eu3+纳米晶的最强发射峰位于589 nm, 对应于Eu3+的5D0-7F1跃迁发射, 说明Eu3+占据LaF3基质中La3+晶格点的C2对称格位上. 同时Eu3+的猝灭摩尔分数为5%, 荧光寿命随着灼烧温度的升高而延长.     

球形La2O3∶Eu纳米晶的制备及其发光特性

The spheric La₂O₃∶Eu nanocrystals were prepared using NH₃·H₂O-NH₄HCO₃ mixture as precipitant. The material was characterized by FTIR, XRD and TEM techniques. The luminescence properties of Eu³⁺ in spheric La₂O₃ were measured by three dimension spectra, emission and excitation spectra. The results indicate that the La₂O₃∶Eu nanocrystals are in hexagonal phase by annealing at 800 ℃, the crystal size is about 30 nm. The maximum emission and excitation wavelength were determined by three dimensional spectroscopy to be at 591 nm and 394 nm, respectively. In emission spectrum the band at 591 nm and 612 nm are corresponding to ⁵D₀-⁷F₁ and ⁵D₀-⁷F₂ transition of Eu³⁺ ions. With increasing in annealing temperature the differences of intensity of the two transitions are increased. This phenomenon shows that the luminescence intensity of La₂O₃∶Eu nanocrystals can be tuned by changing annealing temperature.     

正铌酸镧(LaNbO4)及其掺杂粉体的发光特性

采用化学共沉淀法和高温固相法合成制备得到纯的和掺杂Tb的LaNbO4超细粉体, 并对其发光性能进行了激发和发射光谱分析.测试表明, LaNbO4可被汞线激发, 发射波长处于蓝紫光区; 相比高温固相法, 化学共沉淀法制备的LaNbO4粉末相对发光强度增加3～4倍;Tb的掺杂使(La, Tb)NbO4粉体在汞线激发下发出黄绿色光, (La, Tb)NbO4的基质络离子NbO6发生淬灭, 并对有关机制进行了讨论.     

铁酸钴纳米晶的低温合成、谱学表征及磁性

以十六烷基三甲基溴化铵（CTAB）为模板,Fe(NO3)3·9H2O和Co(NO3)2·6H2O为前躯体,NaOH为沉淀剂,低温回流合成了磁性铁酸钴纳米晶。利用X射线衍射、透射电子显微镜、红外光谱、拉曼光谱等测试技术对产品的结构进行了表征,借助振动样品磁强计测定了样品的室温磁性能。结果表明,铁酸钴纳米晶为单相立方尖晶石结构,纳米晶的平均粒径为15-20 nm。铁酸钴纳米晶在室温外加磁场下表现出明显的磁滞现象,饱和比磁化强度MS=36.5 A.m2/kg,矫顽力HC=5.89×104 A/m。     

单分子磁体[Mn4(CF3COO)4(hmp)6]的合成、晶体结构及磁学性质

以[Mn12O12(CF3COO)16(H2O)4]·2CF3COOH·4H2O和2-羟甲基吡啶(hmpH)为起始物, 在四氢呋喃溶液中合成了一种新的四核锰配合物[Mn4(CF3COO)4(hmp)6]. X射线单晶衍射结果表明, 该配合物属于单斜晶系, P21/c空间群, 晶胞参数a=1.3663(3) nm, b=1.4705(3) nm, c=1.4734(3) nm, β=98.51(3) °, V=2.9276 nm3, Z=2. 配合物中有两个CF3COO-基团与七配位Mn2中心相连, 其中一个为单齿配体, 另一个是双齿配体. 直流磁化率研究结果表明, 该配合物具有较高的自旋基态, 而交流磁化率依赖于外场频率变化极值的出现表明该配合物是一种单分子磁体.     

相位可控的氟钪纳米晶的合成及其上转换发光性能

控制反应条件如表面活性剂的组成、加入量或反应时间,可以制得不同形态、相结构且具有上转换发光(UCL)的氟钪纳米晶(NCs)。改变表面活性剂油酸(OA)/油胺(OM)的比例有利于晶体结构从立方相ScF_3∶Yb,Er转变为具有上转换发光性能增强的正交相KSc_2F_7∶Yb,Er纳米晶,而纳米晶的形态会发生从小到大的转变。改变掺杂元素的种类及含量,在980 nm光激发下,KSc_2F_7纳米晶的上转换发光可以从蓝色变到白色,再到主要发射紫色光。     

Luminescence Properties of Mn2+-Doped Sol-Gel Glasses

Mn²⁺-doped 1Al₂O₃-99SiO₂ glasses have been prepared by a sol-gel method and their photoluminescence (PL) properties have been studied for the first time. The effect of ZrO₂ and TiO₂ on the luminescence properties has also been studied. In addition, the PL of Mn: 1Al₂O₃-99SiO₂ is compared with Mn:SiO₂. The emission spectra of all the samples containing Al₂O₃ show a band around 620 nm, and the sample without Al₂O₃ shows two bands around 620 and 650 nm. These emission bands are all assigned to the ⁴T₁ ⁶A₁ transition of octahedrally coordinated Mn²⁺ · ZrO₂ and TiO₂ have fluorescence quenching effect. The relative fluorescence intensity of Mn²⁺-doped sol-gel 1Al₂O₃-99SiO₂ is much stronger than that of Mn²⁺-doped sol-gel SiO₂. The difference of the emission wavelength between host materials is explained in terms of the ligand field effect.     

纳米晶LaAlO3掺Eu3+的复合沉淀法制备及发光性质

以NH₃·H₂O-NH₄HCO₃混合溶液为复合沉淀剂,制备了LaAlO₃:Eu³⁺纳米晶体.通过X射线衍射、扫描电镜和透射电镜对产物进行了表征,用荧光光度计测试了样品的三维荧光光谱、激发光谱和发射光谱.结果表明:前驱沉淀物经800℃焙烧处理2h,制备出球型形貌,颗粒分散性好、尺寸约为40nm的立方相LaAlO₃纳米晶.由三维荧光光谱确定了LaAlO₃:Eu³⁺的最佳监测波长和激发波长,在395nm波长光的激发下观察到纳米LaAlO₃中Eu³⁺的591nm(⁵D₀-⁷F₁)和613nm(⁵D₀-⁷F₂)特征发射谱,磁偶极跃迁⁵D₀-⁷F₁的发射峰强度要比电偶极跃迁⁵D₀-⁷F₂更强,而且这种趋势随着焙烧温度的升高明显增强,说明由该法制备的纳米LaAlO₃中Eu³⁺离子占据的位置具有高的对称性.     

Mn0.6 Zn0.4 Fe2 O4 磁性亚微球的可控合成及磁性能

采用溶剂热法制备了单分散Mn0.6Zn0.4Fe2O4磁性亚微米球, 研究了反应工艺参数对磁性亚微米球结构形貌、 直径和静磁性能的影响规律. 研究发现, 随着反应时间的延长, 体系中的金属离子首先水解沉淀, 形成羟基氧化铁及Mn, Zn氢氧化物, 然后脱水转化为Mn0.6Zn0.4Fe2O4球形纳米粒子, 这些纳米粒子发生团聚, 形成结构疏松、 大小不均匀的亚微米粒子, 最后通过Ostwald熟化过程, 形成致密的单分散亚微米球. 降低反应溶液的pH值、 增加乙二醇或聚乙二醇的用量, 均会使亚微球的直径增大, 并可在150~500 nm范围内调控微球的粒径; 但组成磁性亚微球的纳米粒子的粒径逐渐减小, 产物的饱和磁化强度增大, 矫顽力和剩磁减小.     

ZrO2∶Tb3+纳米晶的离子交换法制备及其发光特性

以强碱性阴离子交换树脂为交换介质,采用离子交换法制备了稀土Tb3+离子掺杂的ZrO2:Tb3+纳米晶.通过XRD,TG-DSC,TEM,HRTEM等手段分析了样品制备过程的物相变化及晶粒形貌,用荧光光度计研究了样品的三维荧光光谱、激发光谱和发射光谱.结果表明:前驱沉淀物经800℃焙烧处理2 h,制备出近方型形貌,颗粒分散性好、尺寸约为40 nm的四方相ZrO2:Tb3+纳米晶.当焙烧温度升高到900℃以上时样品出现了少量单斜晶相,而经800℃焙烧处理的纯Zr02是以四方相和单斜相同时存在.说明稀土Tb3+离子的掺杂对ZrO2基质的四方晶相起到稳定作用.由ZrO2:Tb3+)的等角三维荧光光谱图显示Tb3+在ZrO2基质中的最佳激发波长为290 nm:在290 nm波长光的激发下观察到纳米ZrO2中Tb3+的发射峰位于491,545,582 nm分别对应于Tb3+的5D4→7F6、5D4→7F5、5D4→7F4、5D4→7F4能级跃迁,以491,545nm的发射峰最强,其中经800℃焙烧处理的样品其5D4→7F6跃迁发射与5D4→7F5跃迁发射强度几乎相同,说明该法制备的纳米ZrO2:Tb3+中5D4→7F6跃迁发射增强,使Tb3+发光的蓝色成分增加了.     

Synthesis,Crystal Structure and Magnetic Properties of Rb2Mn3O4

Rb₂Mn₃O₄, which is the first rubidium oxomanganates(II), has been synthesized via the azide/nitrate route from a stoichiometric mixture of the precursors RbN₃, RbNO₃, and MnO, as well as from Rb₂O and MnO, through an all solid state reaction. Its crystal structure (C2/c, Z = 4, a = 1546.9(2) pm, b = 666.22(7) pm, c = 588.06(6) pm) consists of a 3D arrangement of edge‐ and corner‐sharing MnO₄ tetrahedra with rubidium filling the space between. Magnetic susceptibility measurements indicate a magnetic phase transition at 126 K. The magnetic response as a function of temperature is complex, indicating strong, partly frustrated magnetic exchange interactions.