Presence of intrinsic defects and transition from diamagnetic to ferromagnetic state in Co<Superscript>2+</Superscript> ions doped ZnO nanoparticles

In this paper, we report the structural, morphological and magnetic properties of pure and Co²⁺ doped ZnO nanoparticles synthesized using sol–gel auto combustion method. The prepared nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area diffraction pattern (SAED), Fourier transform infrared spectroscopy (FTIR) and photoluminescence spectroscopy. The analysis of XRD pattern shows the single phase nature with a hexagonal wurtzite structure for the prepared nanoparticles. The average crystallite sizes of the prepared nanoparticles were found in the range 18–19 nm. SEM images showed that pure and Co²⁺ doped nanoparticles have different morphology. The shape of the prepared nanoparticles is approximately hexagonal shown by TEM image. SAED pattern also confirms the wurtzite structure with single crystalline nature. FTIR spectra showed the characteristic vibrations frequency band of Zn–O. Photo luminescence spectrum showed that two emission peaks, which are ascribed to near band edge transitions and broadened intensive green emission associated with oxygen-vacancy defects. The magnetic properties were measured by vibrating sample magnetometer (VSM) and superconducting quantum interference device with field dependant magnetization at 300 K and temperature dependant magnetization from 0 to 300 K. From VSM analysis, pure ZnO nanoparticles show diamagnetic behavior while Co²⁺ doped ZnO nanoparticles revealed ferromagnetic behaviour at room temperature. The significant changes in M–H loop from diamagnetic behavior to ferromagnetic behavior are due to the intrinsic defects such as oxygen vacancies (Vo) and zinc vacancies (Vz_n). The RTFM has been presented in terms of vacancies in the frame of bound magnetic polaron model.     

Effect of inorganic shells on luminescence properties of ZnS:Ag nanoparticles

The hydrothermally synthesized Ag-doped ZnS (ZnS:Ag) nanoparticles have been coated with inorganic shells by a chemical precipitation method. The ZnS:Ag/ZnS, ZnS:Ag/CdS, and ZnS:Ag/ZnO core–shell nanoparticles with different thickness of ZnS, CdS, and ZnO shells have been prepared. The effects of shells on the luminescence properties of ZnS:Ag cores have been investigated through the photoluminescence (PL) spectra and luminescence stabilities of products. In the core–shell nanoparticles involved here, the ZnO shell can most significantly enhance the luminescence of ZnS:Ag cores. The 450 nm emission intensity of ZnS:Ag/ZnO nanoparticles is up to 125 % of that of ZnS:Ag nanoparticles. However, the ZnO shell can hardly influence the luminescence stability under ultraviolet irradiation. The ZnS shell can only increase the luminescence of ZnS:Ag cores to some extent, but it can improve the luminescence stability under ultraviolet irradiation. Although the CdS shell can improve the luminescence stability to some extent, it quenches the luminescence of ZnS:Ag nanoparticles dramatically.     

Influence of microstructure on the luminescence properties of YVO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> nanoparticles

YVO₄:Eu³⁺ nanoparticles were synthesized by hydrothermal method at different conditions. The microstructures and photoluminescence (PL) properties of the as-prepared YVO₄:Eu³⁺ nanoparticles were investigated by X-ray powder diffraction, field emission scanning electron microscopy and PL spectroscopy. The detailed relationship between the microstructures and luminescence properties was investigated. It has been found that the crystallinity, the grain size and the duty factor of Eu³⁺ play important roles in influencing the luminescence properties. The article is published in the original.     

SiNx薄膜中硅纳米粒子的制备及表征

通过等离子增强化学气相沉积(PECVD)法, 以氨气和硅烷为反应气体, P型单晶硅和石英为衬底, 低温下(200℃)制备了含硅纳米粒子的非化学计量比氮化硅(SiN_x)薄膜. 经高温(范围500~950℃)退火处理优化了薄膜结构. 室温下测试了不同温度退火后含硅纳米粒子SiN_x薄膜的拉曼(Raman)光谱、光致发光(PL)光谱及傅立叶变换红外吸收(FTIR)光谱, 对薄膜材料的结构特性、发光特性及其键合特性进行了分析. Raman光谱表明. SiN_x薄膜内的硅纳米粒子为非晶结构. PL光谱显示两条与硅纳米粒子相关的光谱带, 随退火温度的升高此两光谱带峰位移动方向相同. 当退火温度低于800℃时, PL光谱峰位随退火温度的升高而蓝移. 当退火温度高于800℃时, PL光谱峰位随退火温度的升高而红移. 通过SiNx薄膜的三种光谱分析发现薄膜的光致发光源于硅纳米粒子的量子限制效应. 这些结果对硅纳米粒子制备工艺优化和硅纳米粒子光电器件的应用有重要意义.     

Investigation of size dependent structural and optical properties of thin films of CdSe quantum dots

Cadmium selenide (CdSe) quantum dots were grown on indium tin oxide substrate using wet chemical technique for possible application as light emitting devices. The structural, morphological and luminescence properties of the as deposited thin films of CdSe Q-dot have been investigated, using X-ray diffraction, transmission electron microscopy, atomic force microscopy and optical and luminescence spectroscopy. The quantum dots have been shown to deposit in an organized array on ITO/glass substrate. The as grown Q-dots exhibited size dependent blue shift in the absorption edge. The effect of quantum confinement also manifested as a blue shift of photoluminescence emission. It is shown that the nanocrystalline CdSe exhibits intense photoluminescence as compared to the large grained polycrystalline CdSe films.     

Fluorescent magnetic hybrid nanoprobe for multimodal bioimaging

A fluorescent magnetic hybrid imaging nanoprobe (HINP) was fabricated by the conjugation of superparamagnetic Fe3O4 nanoparticles and visible light emitting (～600 nm) fluorescent CdTe/CdS quantum dots (QDs). The assembly strategy used the covalent linking of the oxidized dextran shell of magnetic particles to the glutathione ligands of QDs. The synthesized HINP formed stable water-soluble colloidal dispersions. The structure and properties of the particles were characterized by transmission electron and atomic force microscopy, energy dispersive x-ray analysis and inductively coupled plasma optical emission spectroscopy, dynamic light scattering analysis, optical absorption and photoluminescence spectroscopy, and fluorescent imaging. The luminescence imaging region of the nanoprobe was extended to the near-infrared (NIR) (～800 nm) by conjugation of the superparamagnetic nanoparticles with synthesized CdHgTe/CdS QDs. Cadmium, mercury based QDs in HINP can be easily replaced by novel water-soluble glutathione stabilized AgInS2/ZnS QDs to present a new class of cadmium-free multimodal imaging agents. The observed NIR photoluminescence of fluorescent magnetic nanocomposites supports their use for bioimaging. The developed HINP provides dual-imaging channels for simultaneous optical and magnetic resonance imaging.     

磁性荧光纳米复合粒子的制备及其表面生物功能化

用化学共沉淀法制备了四氧化三铁(Fe3O4)纳米粒子,Stober法在其表面包裹SiO2并复合荧光标记物FITC,EDC偶联牛血清白蛋白(BSA)。采用扫描电子显微镜(SEM),傅里叶变换红外光谱仪(FT-IR),荧光分析仪,电子能谱(XPS)等对复合粒子进行了表征。结果表明,复合粒子保留了FITC的荧光特性、Fe3O4的磁响应性并成功接枝蛋白分子。生物功能化磁性荧光复合纳米粒子有望广泛应用于细胞标记、荧光追踪、磁性分离等领域。     

Temperature dependence of up-conversion luminescence and photoluminescence of Mn2+ in ZnS:Mn2+ nanoparticles

The photoluminescence (excited at both 300 nm and 383.5 nm) and up-conversion luminescence (excited at 767 nm) of the Mn2+ 4T1-->6A1 transition in both bulk and ZnS:Mn2+ nanoparticles have been measured as a function of temperature. The Mn2+ emission spectra shift monotonically to longer wavelengths at lower temperatures, whereas the intensity change of the luminescence is more complex. The complicated temperature behavior is explained by considering the processes of nonradiation relaxation via phonon coupling, exciton thermal dissociation (binding energy), energy transfer, carrier trapping, and the temperature change of the absorption spectra. The fact that the temperature dependence of the 767 nm excited up-conversion luminescence is the same as the 383.5 nm excited photoluminescence in both bulk and nanoparticles supports the conclusion that the up-conversion luminescence is due to two-photon absorption.     

Temperature dependent luminescence of azobenzene capped CdS quantum dots

Cadmium sulfide (CdS) quantum dots (QDs) are prepared at room temperature by "form-fill-seal" method, while the azobenzene is used as surfactant to control the particle size and to prevent agglomeration. The typical size of CdS nanoparticles is estimated as 2 nm by X-ray diffraction. The absorption spectra of CdS QDs are measured at room temperature and a new absorption peak associated with the surface excited state is found. The luminescence property of the CdS QDs is studied at room temperature and low temperature. Two photoluminescence peaks exist in the temperature range of 8-300 K. One peak at 460 nm is attributed to CdS QDs, while the other one at 667 nm comes from the transition of surface excited state and its intensity decreases with temperature increasing.     

Synthesis and characterization of lanthanide-doped sodium holmium fluoride nanoparticles for potential application in photothermal therapy

Upconversion nanoparticles (UC NPs) in combination with plasmonic materials have great potential for cancer photothermal therapy. Recently, sodium holmium fluoride (NaHoF₄) is being investigated for luminescence and magnetic resonance imaging (MRI) contrast agent. Here, we present successful synthesis of excellent quality doped NaHoF₄ NPs for possible UC luminescence application and coated for possible photothermal therapy application. Synthesized NaHoF₄ nanocrystals were doped with Yb/Er and coated with gold, gold/silica, silver and polypyrrole (PPy). XRD, XPS and TEM were used to determine structure and morphology of the NPs. Strong UC photoluminescence (PL) emission spectra were obtained from the NPs when excited by near-infrared (NIR) light at 980 nm. Cell viability and toxicity of the NPs were characterized using pancreatic and ovarian cancer cells with results showing that gold/silica coating produced least toxicity followed by gold coating.     

Zinc oxide nanoparticles: A study of defect level blue-green emission

Systematic investigation of the structural, morphological and optical properties of hexylamine capped zinc oxide (ZnO) nanoparticles is presented. Optical properties indicate the presence of sufficient amount of surface defects. These defects in highly dispersed ZnO nanoparticles have been studied by annealing the nanoparticles in air at various temperatures and recording the photoluminescence spectra. The annealing temperature was found to strongly influence the UV band edge emission and the blue-green defect level emission (DLE). At low annealing temperatures an increase in UV emission with temperatures is observed and this emission is proposed to be a result of desorption of surface adsorbed water and hydroxyl groups. The DLE of the synthesized sample is likely due to the presence of oxygen vacancies on the surface resulting in green emission.     

Influence of Co-doping on the structural, optical and magnetic properties of ZnO nanoparticles synthesized using auto-combustion method

In the present work, we have interested to understand the influence of cobalt doping on the various properties of ZnO nanoparticles, a series of samples were successfully synthesized using sol–gel auto-combustion method. The effects of Co doping on the structural and optical properties of ZnO:Co nanoparticles were investigated using X-ray diffraction (XRD), scanning electron microscopy, fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible spectroscopy, photoluminescence spectroscopy and vibrating sample magnetometer (VSM). With the sensitivity of the XRD instrument, the structural analyses on the undoped and Co-doped ZnO samples reveal the formation of polycrystalline hexagonal-wurtzite structure without any secondary phase. FTIR spectra confirm the formation of wurtzite structure of ZnO in the samples. The optical absorption spectra showed a red shift in the near band edge which indicates that Co²⁺ successfully incorporated into the Zn²⁺ lattice sites. The room temperature PL measurements show a strong UV emission centered at 392 nm (3.16 eV), ascribed to the near-band-edge emissions of ZnO and defect related emissions at 411 nm (violet luminescence), 449 nm (blue luminescence) and 627 nm (orange-red luminescence), respectively. Magnetic study using VSM reveals that all the samples are found to exhibit room temperature ferromagnetism.     

Effect of 8 MeV electron beam irradiation on the structural and optical properties of CeO2 nanoparticles

The effect of 8 MeV electron beam irradiation on the structural and optical properties of cerium oxide nanoparticles was investigated. Ceria nanoparticles were synthesized by chemical precipitation method, and characterized by X-ray diffraction, transmission electron microscopy, ultraviolet–visible, photoluminescence and Raman spectroscopy. Ultraviolet–visible absorption spectra, photoluminescence and Raman spectra of beam irradiated samples were modified, and shifted to blue region, which were attributed to quantum size effect. Systematic observations found that nonstoichiometry, defects and size reduction caused by beam irradiation have great influence on optical band gap, blue shift, photoluminescence and Raman band modifications. Moreover, electron beam irradiation is a suitable technique to enhance the structural and optical properties of nanoceria by controlling the particle size, which may lead to potentially useful technological applications.     

Structural and optoelectronic characterization of prepared and Sb doped ZnO nanoparticles

This paper briefly reports the structural and optoelectronics properties of prepared pure and Sb doped ZnO nanoparticles. Doping with suitable elements offers an efficient method to control and enhance the optical properties of ZnO nanoparticles, which is essential for various optoelectronics applications. Sb doped ZnO nanoparticles have significant concern due to their unique and unusual electrical and optical properties. In the present work, we report the synthesis of Sb doped ZnO successfully with average particle size range from 26 to 29 nm via direct precipitation method. The phase purity and crystallite size of synthesized ZnO and Sb doped nano-sized particles were characterized and examined via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The elemental analyses of undoped and doped ZnO nanoparticles were examined by using energy-dispersive X-ray spectroscopy (EDAX).We investigated and measured the optoelectronics properties of synthesized ZnO and Sb doped ZnO nanoparticles by employing photoluminescence and UV–Visible spectroscopy. The influence of Sb doping on photoluminescence (PL) spectra of ZnO nanoparticles, which consists of UV emission and broad visible emission band, is found to be strongly dependent upon the Sb concentration for all the Sb doped ZnO nanoparticles samples under investigation. The UV–Visible absorption study shows an increase in band gap energy as Sb is incorporated on the ZnO nanoparticles.     

Optical and electrophysical properties of Ag–PEPC nanocomposites

Absorption and luminescence spectra as well as the temperature dependences of electrical conductivity of polyepoxypropylcarbazole (PEPC) with Ag nanoparticles are studied. Polyepoxypropylcarbazole results in an additional stabilization of Ag nanoparticles. They cause essential PEPC photoluminescence quenching. An additional maximum in the luminescence spectrum appeared to be decreasing in time, probably due to some photochemical reaction. Metallic type of conductivity appeared at intermediate temperatures even with rather low concentration of nanoparticles.     

Synthesis and characterization of porous ZnO nanoparticles by hydrothermal treatment of as pure aqueous precursor

The presence of the complexing agents in the growth solution poses risk of the unintentional doping in the synthesized product and hence is likely to adversely affect the intrinsic properties. Herein we report the synthesis of ZnO nanoparticles with porous microstructure using pure aqueous precursor. Crystalline ZnO nanoparticles were synthesized by thermal treatment of aqueous solution of zinc acetate in an open bath. The size of the nanocrystals was controlled by changing the initial precursor concentration. The structural and optical properties of the synthesized nanocrystals were analyzed by X-ray diffraction, high resolution transmission electron microscopy, UV-vis absorption and room temperature photoluminescence measurement techniques. The TEM and UV-vis spectral signature analyses confirmed the formation of dispersed single crystalline ZnO nanoparticles. The nanopowders were found to have disordered mesoporous structure. The synthesized nanocrystals exhibited characteristic band edge emission as well as to surface defect related deep level visible luminescence.     

Effects of the host morphologies on luminescence properties of Nd(3+)-doped LaF3 nanoparticles

By using different surfactants, several host morphologies including rod-like, pot-like and shuttle-like of LaF3:Nd3+(1% mol) nanoparticles were prepared by a simple microemulsion hydrothermal method, and their properties were characterised by XRD, TEM and photoluminescence spectroscopy. The experimental results indicated that the rod-like and pot-like nanocrystals possess well shaped hollow structures. The analysis of spectra proved that the local environment around the dopant ion changed with the different host morphology, which in turn influenced the luminescence properties. The luminescence lifetimes derived from biexponential fitting were 615 micros (nanopots), 419 micros (nanorods) and 194 micros (nanoshuttles), respectively. This phenomenon is ascribed to the weakening effect of hollow or fenestral structures to the nonradiative ratio.     

Optical characterization of Er-doped ZnSe for scintillation applications

The effect of Er-doping of ZnSe crystals on luminescence and structural properties was investigated using low-temperature photoluminescence, X-ray luminescence, Raman and IR spectroscopies. It was found that Er dopant atoms with the concentration in the solid phase of about 10⁻³ wt.% lead to a substantial disordering of initial crystalline structure. The mentioned processes manifest in substantial decrease of the amplitudes of corresponding vibrational modes and increase of their FWHM in first-order Raman spectra of Er-doped ZnSe crystals. Also, Er-doping stimulates an appearance of additional absorbance bands in IR transmittance spectra. However, Er-doping leads to substantial increase of the efficiency of photoluminescence and X-ray luminescence that is very important for scintillation application. In this case, the luminescence is mainly caused by recombination via defect centers which contain Er atoms incorporated in the ZnSe lattice in different electronic configurations.     

Synthesis,characterization and studies on optical properties of hierarchical ZnO–CdS nanocomposites

Cadmium sulfide coated zinc oxide hierarchical nanocomposites have been synthesised at room temperature by a simple solution based method. CdS nanoparticles were deposited on the surface of ZnO without using any surfactant, ligand or chelating agents. The nanocomposites were synthesised using different concentrations of thioacetamide, cadmium salts, and also by varying the reaction time. After characterization of the nanocomposites, optical properties were investigated by UV–visible diffuse reflectance and photoluminescence spectroscopy techniques. It was found that band gap of the ZnO–CdS nanocomposites is tunable between 2.42 and 3.17 eV.     

Photoluminescence of Si nanocrystallites and amorphous oxygen-containing si nanoparticles: the reversible effect of ambient atmosphere on luminescence

Si nanocrystallites of various sizes and oxygen-containing Si nanoparticles with different oxygen contents were prepared by vapor condensation. The Si nanocrystallites showed a visible light emission from 500 nm to 900 nm with the peak at 800 nm, and the intensity of photoluminescence increased with decreasing the particle size. This photoluminescence observed in vacuum could be quenched by air and hydrogen, and reappeared after the sample chamber was evacuated. The oxygen-containing Si nanoparticles consisting mainly of Si oxide were amorphous and had an average particle size of approximately 20 nm. Increasing the oxygen content of nanoparticles caused a blueshift of the absorption edge in the transmission spectra. A blue-green photoluminescence with two peaks at 500 nm and 800 nm was observed from these oxygen-containing Si nanoparticles. The luminescence intensity increased with the oxygen content of nanoparticles, and was very sensitive to the ambient atmosphere. Much lower intensity was observed in air, but higher intensity could be recovered in vacuum. Surface states and oxygen-induced luminescent centers were proposed to be responsible for the photoluminescence from the Si nanocrystallites and oxygen-containing Si nanoparticles, respectively. The reversible ambient effect in both cases could be explained by surface charge redistribution during the gas adsorption and desorption processes.