Upconversion luminescence from CdSe nanoparticles

Efficient upconversion luminescence has been observed from CdSe nanoparticles ranging in size from 2.5 to 6 nm. The upconversion luminescence exhibits a near-quadratic laser power dependence. Emissions from both excitons and trap states are observed in the upconversion and photoluminescence spectra, and in the upconversion luminescence the emission from the trap states is enhanced relative to the trap-state emission in the photoluminescence. The upconversion decay lifetimes are slightly longer than the photoluminescence decay lifetimes. Time-resolved spectral measurements indicate that this is due to the involvement of long decay components from surface or trap states. Both the photoluminescence and upconversion luminescence decrease in intensity with increasing temperature due mainly to thermal quenching. All the observations indicate that trap states work as emitters rather than as intermediate states for upconversion luminescence and that two-photon absorption is the likely excitation mechanism.     

Surface passivated silicon nanocrystals with stable luminescence synthesized by femtosecond laser ablation in solution

We report the synthesis of silicon nanocrystals via a one-step route, namely, femtosecond laser ablation in 1-hexene under ambient conditions. The size of these silicon nanocrystals is 2.37 ± 0.56 nm as determined by transmission electron microscopy. Fourier transform infrared spectra and X-ray photoelectron spectra indicate that the surface of the silicon nanocrystals is passivated by organic molecules and is also partially oxidized by O(2) and H(2)O dissolved in the solution. These silicon nanocrystals emit stable and bright blue photoluminescence. We suggest that the photoluminescence originates from the radiative recombination of electron-hole pairs through the oxide-related centers on the surface of the silicon nanocrystals. The decay rate of the oxide-related surface recombination can be comparable to that of the direct band gap transition. In the excitation and emission spectra, a vibrational structure with nearly constant spacings (0.18 eV) is observed. We propose that the strong electron-phonon coupling between excitons and the longitudinal optical (LO) phonons of the Si-C vibration is responsible for this vibrational structure. The fluctuations in the peak resolution, about ±0.01 eV, are ascribed to the size distribution and presence of Si-O vibrations. These silicon nanocrystals offer stable luminescence and are synthesized through a "green" and simple route. They may find important applications in many fields, such as bioimaging and environmental science.     

Preparation of yttrium oxysulfide phosphor nanoparticles with infrared-to-green and -blue upconversion emission using an emulsion liquid membrane system

Yttrium oxysulfide upconverting phosphor nanoparticles, doped with Yb as a sensitizer and Er (or Ho, Tm) as an activator, have been prepared via a solid-gas reaction using precursor oxalate particles obtained in an emulsion liquid membrane (ELM, water-in-oil-in-water (W/O/W) emulsion) system. The resulting Y(2)O(2)S:Yb,Er particles, mainly smaller than 50 nm in diameter, demonstrated green upconversion emission under infrared excitation (lambdaex = 980 nm) via a two-photon process. Distinct green and blue upconversion emission were also demonstrated under the same infrared excitation from Y(2)O(2)S:Yb,Ho and Y(2)O(2)S:Yb,Tm nanoparticles, respectively. These upconverting phosphor nanoparticles, together with Y(2)O(3):Yb,Er infrared-to-red upconverting phosphor particles, with different emission under the same infrared excitation may be applied to the luminescent reporter materials for the detection of the targeted analyte in multiplexed assays.     

Monodisperse and core-shell-structured SiO2@YBO3:Eu3+ spherical particles: synthesis and characterization

Y0.9Eu0.1BO3 phosphor layers were deposited on monodisperse SiO2 particles of different sizes (300, 570, 900, and 1200 nm) via a sol-gel process, resulting in the formation of core-shell-structured SiO2@Y0.9Eu0.1BO3 particles. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and cathodoluminescence (CL) spectra as well as lifetimes were employed to characterize the resulting composite particles. The results of XRD, FE-SEM, and TEM indicate that the 800 degrees C annealed sample consists of crystalline YBO3 shells and amorphous SiO2 cores, in spherical shape with a narrow size distribution. Under UV (240 nm) and VUV (172 nm) light or electron beam (1-6 kV) excitation, these particles show the characteristic 5D0-7F1-4 orange-red emission lines of Eu3+ with a quantum yield ranging from 36% (one-layer Y0.9Eu0.1BO3 on SiO2) to 54% (four-layer Y0.9Eu0.1BO3 on SiO2). The luminescence properties (emission intensity and color coordinates) of Eu3+ ions in the core-shell particles can be tuned by the coating number of Y0.9Eu0.1BO3 layers and SiO2 core particle size to some extent, pointing out the great potential for these particles applied in displaying and lightening fields.     

长波敏化发光铕配合物纳米粒子的制备与表征

以牛血清白蛋白(BSA)为保护剂, 利用沉淀法制备了平均粒径为35 nm的Eu(tta)3dpbt (dpbt = 2-(N,N-二乙基苯胺-4-基)-4,6-二(3,5-二甲基吡唑-1-基)-1,3,5-三嗪, tta = 噻吩甲酰三氟丙酮负离子)荧光纳米粒子. BSA保护Eu(tta)3dpbt纳米粒子在水中分散稳定性高, 光稳定性好, 长波敏化发光性能优良. 其在可见光区激发峰位于415 nm, 激发峰尾部延展至470 nm, 发光量子产率为0.20 (λex=415 nm, 25 ℃). 在近红外双光子激发下可发出纯正的红光, Eu(tta)3dpbt纳米粒子最大双光子激发作用截面为2.4×10⁵ GM (λex=830 nm, 1 GM=10^-50 cm⁴·s·photo^-1·particle^-1).     

Photoluminescence from water-soluble BSA-protected gold nanoparticles

The photoluminescence from water-soluble gold nanoparticles, each composed of a 5.1 nm gold core and a bovine serum albumin (BSA)-protected layer, has been observed. The maximal excitation and the maximal emission wavelength are at 320 and 404 nm, respectively. The photoluminescence quantum yield is estimated as 0.053+/-0.0070, at room temperature. The mechanism of the luminescence is hypothesized to be associated with interband transitions between the filled 5d(10) band and 6(sp)(1) conduction band. The photoluminescence is sensitive to pH, organic solvents and metal ions. These observations suggest that this nanoparticles are a viable alternative to organic fluorophores or semiconductor nanoparticles for biological labeling and imaging.     

球形Y2O2S∶Yb,Ho上转换粒子的合成及其尺寸相关的发光机制研究

采用改进的均匀沉淀法结合固-气硫化工艺制备了一系列Y2O2S∶Yb, Ho上转换粒子. 利用X射线晶体衍射(XRD)和透射电子显微镜(TEM)对粒子的结构和形貌进行了表征, 并通过上转换发光光谱(UCL)和红外光谱(FTIR)研究了粒子的上转换发光性质. XRD和TEM结果表明, 所制备的样品均为单一的六方相结构, 且所有粒子均呈单分散和尺寸均一的球形, 其尺寸分别为40, 80和200 nm. 根据发光强度和激发功率间的对数关系曲线发现, 随着粒子尺寸的降低, 蓝光发射由三光子吸收过程转变为双光子吸收过程; 而绿光和红光发射虽然一直保持双光子吸收过程, 但其对数曲线斜率均随粒子尺寸的降低而逐渐增大. 对该材料的粒子尺寸与上转换发光机制的关系进行了讨论.     

Photoluminescence Properties of Surface-Modified Nanocrystalline ZnS : Mn

DBS surface-modified nanocrystalline ZnS : Mn was prepared by a precipitation method. Photoluminescence spectra and decay curves were measured and compared to those of unmodified samples. For both kinds of samples, luminescence decay curves of 600 nm emission consist of two components with nanosecond (ns) and millisecond (ms) lifetimes. The nanosecond component is attributed to zinc vacancies luminescence, with peak located at 440 nm. While the millisecond component is attributed to Mn(2+) luminescence and its decay time changes with Mn(2+) concentration and surface modification. The surface-modified sample has a longer lifetime compared to unmodified samples. The photoaging of surface-modified samples is slow. Particle size effects on photoaging were also examined. For nanocrystalline ZnS : Mn photoaging is more noticeable than that of bulk material. After UV irradiation, photoluminescence intensity of the modified sample is several times larger than that of the unmodified sample, because the surface-active reagent decreases surface defects and depresses radiationless transitions. XPS yields direct evidence of the surface-modification effect on the surface structure. Copyright 2000 Academic Press.     

Spectroscopy property of Ag nanoparticles

Three silver nanoparticles of different size characterized by the UV-vis absorbance spectra and TEM images were prepared by citrate reduction and laser ablation with excitation of 532 and 248 nm. It is proved that all of them are effective SERS-active substrates, whereas, enhancement effect of silver colloids has not too much relation with the size and shape of the Ag nanoparticles. However, different photoluminescence spectra were observed from these three particles, indicating that the photoluminescence property of silver nanoparticles is dependent on the size. The spectra shift to higher energies with decreasing particle size. In addition, we also tentatively give the assignment of the luminescence bands.     

Ca掺杂的Ba2Al2Si10N14O4∶Eu2+荧光粉发光性能

通过固相反应制备了系列Ca掺杂的Ba2Al2Si10N14O4∶Eu2+绿色荧光粉,发现当半径较大的Ba被Ca取代后导致了晶格的收缩,通过X射线衍射(XRD)测量和Unitcell软件计算发现Ca的最大掺杂量在20%。Ca掺入Eu0.4Ba1.6Al2Si10N14O4荧光粉后,可有效地提高光转换性能,并使激发光谱发生一定程度的红移和宽化,从而被近紫外宽波段光有效激发,与近紫外LED的发射光谱匹配。同时Ca的掺杂也使发射光谱发生了可控的红移,可以由520 nm的绿光红移至548 nm的黄光区域。进一步发现Eu2+的淬灭浓度随着20%Ca的掺入而降低,这是由于Ca掺入导致的晶格收缩使Eu2+离子间距离减小。最后在CIE色度图中对不同Ca,Eu浓度的荧光粉的色坐标位置进行比较,发现可通过Ca,Eu浓度的变化在很大范围内调制荧光粉的发光性能。     

Highly luminescent silicon nanocrystals with discrete optical transitions.

A new synthetic method was developed to produce robust, highly crystalline, organic-monolayer passivated silicon (Si) nanocrystals in a supercritical fluid. By thermally degrading the Si precursor, diphenylsilane, in the presence of octanol at 500 degrees C and 345 bar, relatively size-monodisperse sterically stabilized Si nanocrystals ranging from 15 to 40 A in diameter could be obtained in significant quantities. Octanol binds to the Si nanocrystal surface through an alkoxide linkage and provides steric stabilization through the hydrocarbon chain. The absorbance and photoluminescence excitation (PLE) spectra of the nanocrystals exhibit a significant blue shift in optical properties from the bulk band gap energy of 1.2 eV due to quantum confinement effects. The stable Si clusters show efficient blue (15 A) or green (25-40 A) band-edge photoemission with luminescence quantum yields up to 23% at room temperature, and electronic structure characteristic of a predominantly indirect transition, despite the extremely small particle size. The smallest nanocrystals, 15 A in diameter, exhibit discrete optical transitions, characteristic of quantum confinement effects for crystalline nanocrystals with a narrow size distribution.     

Luminescent nanoparticles prepared by encapsulating lanthanide chelates to silica sphere

The luminescent nanoparticles were prepared by encapsulating the [LnL₄]^? (Ln = Eu, Tb; L = BTFA, HFAA, TTFA, TFAA) complexes anion into the silicon framework. We firstly synthesized a series of novel siloxy-bearing lanthanide complex precursor, and then encapsulated them into the silica sphere by a modified Stöber process. As a result, four europium and two terbium tetrakis β-diketonate complexes functionalized silica sphere nanoparticles were obtained and characterized in detail using Fourier transform infrared spectra, X-ray diffraction, scanning electronic microscope, thermogravimetric analysis, luminescence excitation and emission spectroscopy, luminescence lifetime measurements, and diffuse reflectance UV–Vis spectroscopy. The result shows that these luminescent nanoparticles maintain the distinctive luminescence character of lanthanide chelate including broad excitation spectra, line-like emission spectra, high quantum efficiency, and long luminescent lifetime, which makes them great potential application in the synthesis of luminescent nanoparticle.     

Folate-receptor-mediated delivery of InP quantum dots for bioimaging using confocal and two-photon microscopy

A novel method for the synthesis of highly monodispersed hydrophillic InP-ZnS nanocrystals and their use as luminescence probes for live cell imaging is reported. Hydrophobic InP-ZnS nanocrystals are prepared by a new method that yields high-quality, luminescent core-shell nanocrystals within 6-8 h of total reaction time. Then by carefully manipulating the surface of these passivated nanocrystals, aqueous dispersions of folate-conjugated nanocrystals (folate-QDs) with high photostability are prepared. By use of confocal microscopy, we demonstrate the receptor-mediated delivery of folic acid conjugated quantum dots into folate-receptor-positive cell lines such as KB cells. These folate-QDs tend to accumulate in multi-vescicular bodies of KB cells after 6 h of incubation. Receptor-mediated delivery was confirmed by comparison with the uptake of these particles in folate-receptor-negative cell lines such as A549. Efficient two-photon excitation of these particles and two-photon imaging using these particles are also demonstrated. The use of these InP-ZnS nanoparticles and their efficient two-photon excitation can be potentially useful for deep tissue imaging for future in vivo studies.     

Two-photon excitation of substituted enediynes

Electronic spectroscopy of nine benzannelated enediynes and a related fulvene was studied under one-photon and two-photon excitation conditions. We utilize measured absorbance and emission spectra and time-resolved fluorescence decays of these molecules to calculate their radiative lifetimes and fluorescence quantum yields. The fluorescence quantum yields for the other compounds were referenced to the fluorescence quantum yield of compound 3 and used to determine relative two-photon absorption cross-sections. Further insight into experimental studies has been achieved using time-dependent density functional (TD-DFT) computations. The probability of two-photon absorption (TPA) increases noticeably for excitation to the higher excited states. The photophysical properties of benzannelated enediynes are sensitive to substitutions at both the core and the periphery of the enediyne chromophore. Considerably enhanced two-photon absorption is observed in an enediyne with donor substitution in the middle and acceptor substitution at the termini. Excited states with B symmetry are not active in TPA spectra. From a practical point of view, this study extends the range of wavelengths applicable for activation of the enediyne moiety from 350 to 600 nm and provides a rational basis for future studies in this field. Our theoretical computations confirmed that lowest energy TPA in benzannelated enediynes involves different orbitals than lowest energy one-photon absorbance and provided further support to the notion that introduction of donor and acceptor substituents at different ends of a molecule increases TPA.     

Highly luminescent Eu3+ chelate nanoparticles prepared by a reprecipitation-encapsulation method

Aqueous suspensions of highly luminescent Eu3+ chelate nanoparticles are prepared by a novel reprecipitation-encapsulation method. An alkyl alkoxysilane encapsulation agent is included during the nanoparticle formation process, forming a nanoparticle encapsulation layer that inhibits aggregation as evidenced by UV-vis spectroscopy and atomic force microscopy. In addition, the encapsulated nanoparticles exhibit a small size (10 nm), intense luminescence, and excellent photostability. We estimate that the molar extinction coefficients of the approximately 10 nm particles are approximately 5.0x10(7) M-1 cm-1 with a luminescence quantum yield of 6%, indicating a luminescence brightness many times larger than that of conventional fluorescent dyes and comparable to that of colloidal semiconductor quantum dots. The small size, high brightness, highly red-shifted luminescence, and long luminescence lifetimes of the nanoparticles are of interest for luminescence labeling and sensing applications.     

EuBO3的低温水热合成及光谱可调性质研究

采用低温水热法合成了稀土硼酸盐EuBO3的纯相样品.利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱仪(XPS)和荧光光谱仪(PL)对样品的结构、形貌、价态及发光性质进行了研究.结果表明,该样品属六方晶系,在不同的矿化剂和碱度下呈现不同的自组装形貌.当以NaOH或NH3.H2O为矿化剂时,该样品分别沿着(100)和(002)晶面生长.因为Eu离子以混合价态形式存在,样品表现出光谱可调性,当激发波长为270～360 nm时,样品荧光由红色转为橙色,经粉紫光变为蓝光.     

硅掺杂碳量子点荧光猝灭法测定水样中铜(Ⅱ)

3-氨丙基三甲氧基硅烷(APTMS)与戊二醛(GA)混合前驱物合成的硅掺杂碳量子点(SDCQDs),其最大吸收、激发和发射波长分别为259,245,395 nm,量子产率为13.60%,XPS谱图表明碳量子点掺杂Si,且富含甲亚胺基团和硅氧键。Cu~(2+)对碳量子点荧光产生猝灭作用,依据Cu~(2+)浓度与碳量子点荧光强度猝灭率的相关性,建立碳量子点荧光探针测定水样中Cu~(2+)的分析方法,其它金属离子对Cu~(2+)干扰程度较小,回收率为91.4%~100.8%,检出限为0.13μmol/L,相对标准偏差为0.20%~0.92%。     

固态发光碳纳米粒子的制备及在潜指纹成像中的应用

采用热分解法, 以柠檬酸钠和尿素为前驱体, 通过控制反应温度制备了不需要结合任何固体分散基质即可呈现明亮固态发光的碳纳米粒子(CNPs). 利用X射线衍射(XRD), 透射电子显微镜(TEM), X射线光电子能谱(XPS)、 紫外-可见吸收光谱(UV-Vis)和光致发光光谱(PL)等对CNPs的物相、 形貌和粒径、 表面基团及光学特性进行了表征. 结果表明, 该CNPs为无定形碳结构, 准球形形貌, 粒径分布在5~15 nm范围, 其表面存在C=O, C=N和O=C—N等基团. CNPs的水溶液和固体粉末在365 nm紫外光辐射下, 均呈现明亮的蓝绿色发光. 将该CNPs粉末用作荧光试剂可直接显现不同非渗透性客体表面的潜指纹(LFPs). 在365 nm紫外光激发下, CNPs粉末刷显后的LFPs细节特征清晰可辨, 强荧光背景客体表面的LFPs获得了高对比度的显现效果. 同时, 老化30 d的LFPs利用CNPs粉末也能够显现出可识别的指纹细节. CNPs发光粉末作为指纹试剂在刑侦领域具有潜在的应用前景.     

基于玉米淀粉制备绿色碳量子点及氢离子/氢氧根 离子调节荧光开关性能

以玉米淀粉为碳源,在草酸的作用下利用乙醇溶剂热法制备了一种绿色荧光碳量子点(G-CQDs).通过透射电子显微镜(TEM)、傅里叶红外光谱(FT-IR)、X射线衍射(XRD)、X射线光电子能谱(XPS)和Raman光谱等测试分析了G-CQDs的形貌、组成和结构.结果表明,G-CQDs为粒径为2～5 nm的准球形纳米颗粒,...     

多羧酸根铕二元配合物的合成及光谱分析

分别以1,3,5-苯三甲酸(H₃BTC)、苯六甲酸(H₆MTA)和1,2,3,4,5,6-环己六甲酸(H₆CCA)为配体合成了Eu(III)的二元发光配合物Eu(BTC)·2H₂O, Eu₂(MTA)·4H₂O 和Eu₂(CCA)·4H₂O. 通过元素分析、红外光谱和等离子体原子发射光谱对其化学组成进行了结构表征, 表征结果与理论吻合良好. 利用荧光分度计, 研究了所制备配合物室温条件下的荧光性能(荧光激发光谱、发射光谱、荧光寿命和量子效率), 结果表明: 该三种配合物在紫外光照射下, 均发射Eu(III)离子的特征红光, 其中Eu₂(MTA)·4H₂O(量子效率＝10.25%, 荧光寿命＝0.36 ms)的荧光性能最好, 这说明配体H₆MTA 的能级与Eu³⁺离子能级匹配程度很好. 另外, 通过热分析对配合物的热稳定性进行了分析, 结果表明: 该三种配合物均具有良好的热稳定性, 主要分解温度远高于其他β-二酮配合物.