Fabrication of P(NIPAAm-<Emphasis Type="Italic">co</Emphasis>-AAm) coated optical-magnetic quantum dots/silica core-shell nanocomposites for temperature triggered drug release,bioimaging and in vivo tumor inhibition

ZnS:Mn²⁺ quantum dots (QDs) Fe₃O₄ QDs/SiO₂/P(NIPAAm-co-AAm) core-shell-shell nanocomposites have been successfully fabricated by free radical polymerization method. The average diameter and LCST of ZnS:Mn²⁺ QDs Fe₃O₄ QDs/SiO₂/P(NIPAAm-co-AAm) (NIPAAm:AAm=90:10) nanocomposites was about 200?nm and 41.1°. It possessed a strong yellow-orange emission peak centered at 589?nm from the Mn^{2+ 4}T₁-⁶A₁ transition and the desired superparamagnetic property at room temperature. The DOX encapsulation efficiency and loading capacity was 88% and 15.3 wt%, respectively. The nanocomposites showed the faster drug release behavior at 43?°C than that at 25?°C in vitro release experiment, and exhibited no significant cytotoxicity against the HeLa, HepG2 and HEK293 cell lines. Red fluorescence was observed in the cytoplasm of HeLa cells, confirming its application for biolabeling. Effective tumor inhibition was realized in vivo without the induction of toxicity in mice.

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ZnS:Mn²⁺ (QDs) Fe₃O₄ QDs/SiO₂/P(NIPAAm-co-AAm) nanocomposites showed the red fluorescence in the cytoplasm of HeLa cells, faster drug release behavior at 43?°C than that at 25?°C in vitro, and effective tumor inhibition in vivo, confirming its application for drug delivery.

     

Fabrication and optical properties of ZnS:Mn2+ quantum dots/SiO2 nanocomposites

ZnS:Mn²⁺ quantum dots (QDs)/SiO₂ nanocomposites were successfully synthesized by stöber method. The results showed that the Mn²⁺ ions were substitutionally incorporated into the ZnS host and the average size of the ZnS:Mn²⁺ (5 %) QDs was about 5.5 nm. The yellow–orange emission from the Mn^{2+ 4}T₁–⁶A₁ transition was observed in the photoluminescence spectra, the peak intensity increased as the Mn²⁺ doped ratio increased, and showed a maximum when the concentration of the Mn²⁺ ions kept at 3 %. As the hydrolysis time of tetraethyl orthosilicate increased, the intensity of the yellow–orange emission reached the highest value when t = 4 h for the ZnS:Mn²⁺ (5 %) QDs/SiO₂ nanocomposites.     

Chitosan-encapsulated ZnS : M (M: Fe<Superscript>3+</Superscript> or Mn<Superscript>2+</Superscript>) quantum dots for fluorescent labelling of sulphate-reducing bacteria

Chitosan-encapsulated Mn²⁺ and Fe³⁺-doped ZnS colloidal quantum dots (QDs) were synthesized using chemical precipitation method. Though there are many reports on bio-imaging applications of ZnS QDs, the present study focussed on the new type of microbial-induced corrosive bacteria known as sulphate-reducing bacteria, Thiobacillus novellus. Sulphate-reducing bacteria can obtain energy by oxidizing organic compounds while reducing sulphates to hydrogen sulphide. This can create a problem in engineering industries. When metals are exposed to sulphate containing water, water and metal interacts and creates a layer of molecular hydrogen on the metal surface. Sulphate-reducing bacteria then oxidize the hydrogen while creating hydrogen sulphide, which contributes to corrosion for instance, in pipelines of oil and gas industries. In this study, detection and labelling of sulphate-reducing bacteria is demonstrated using fluorescent QDs. Chitosan capped ZnS QDs were synthesized using dopants at different doping concentrations. UV–Vis spectroscopy, XRD and FTIR characterizations were done to identify the optical band gap energy, crystal planes and determine the presence of capping agent, respectively. The morphology and the average particle size of 3.5 ± 0.2 nm were analysed using TEM which substantiated UV–Vis and XRD results. Photoluminescence spectroscopy detected the bacteria attachment to the QDs by showing significant blue shift in bacteria conjugated ZnS QDs. Fluorescence microscopy confirmed the fluorescent labelling of QDs to Thiobacillus novellus bacteria cells making them ideal for bio-labelling applications.     

Green synthesis of white-light-emitting ZnSe:Eu<Superscript>2+</Superscript>, Mn<Superscript>2+</Superscript> quantum dots in an aqueous solution

High-quality ZnSe:Eu, Mn quantum dots (QDs) with white light emitting were synthesized via a green preparation method in an aqueous solution using thioglycolic acid as a stabilizing agent. The composition of the QDs could be flexibly controlled by varying the amount of Eu or Mn cation. The effects of reflux time and Eu²⁺ ion dopant concentration on the luminescence properties were systematically investigated. The obtained QDs were characterized by photoluminescence spectrometry, X-ray powder diffraction, and high-resolution transmission electron microscopy. The proposed method formed cubic ZnSe:Mn²⁺, Eu²⁺ QDs with the maximum emission peak at 460 and 580 nm. In the optimal condition, the quantum yields of ZnSe:Mn²⁺, Eu²⁺ QDs could reach 27.68%. The CIE color coordinates were (0.328, 0.334), which agreed with those of pure white light (0.33, 0.33). The results verified that the ZnSe:Mn²⁺, Eu²⁺ QDs exhibited potential in light-emitting diode applications.     

Effect of Mn<Superscript>2+</Superscript> doping on the temperature coefficient of capacitance of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>-doped BaTiO<Subscript>3</Subscript> ceramics

The effect of Mn²⁺ on the temperature coefficient of capacitance (TCC) of TiO₂/SiO₂-doped BaTiO₃ ceramics has been investigated. The experiment has shown that the high temperature peak of TCC exhibited a continuous enhancement when Mn²⁺ concentration increased and X8R specification was gradually met. The secondary phase Ba₂TiSi₂O₈ was found in all samples. SEM and XRD analyses have proved that Mn²⁺ could depress the crystallization of TiO₂/SiO₂ in BaTiO₃ ceramics. The microstrain study through MAUD analysis depicted that the high temperature peak of TCC was dependent on the microstrain of samples to a certain extent. The Mn²⁺ could be a useful dopant for ameliorating the TCC of TiO₂/SiO₂-doped BaTiO₃ ceramics. The text was submitted by the authors in English.     

Synthesis,tunable luminescence and thermal stability of Mg<Subscript>2</Subscript>Al<Subscript>4</Subscript>Si<Subscript>5</Subscript>O<Subscript>18</Subscript>:Ce<Superscript>3+</Superscript>/Mn<Superscript>2+</Superscript> phosphors

Ce³⁺/Mn²⁺ singly doped and codoped Mg₂Al₄Si₅O₁₈ phosphors were synthesized by a solid state reaction. The phase, luminescent properties and thermal stability of the synthesized phosphors were investigated. Ce³⁺ and Mn²⁺ singly doped Mg₂Al₄Si₅O₁₈ phosphors show emission bands locating in blue and yellow–red regions, respectively. In Ce³⁺ and Mn²⁺ codoped Mg₂Al₄Si₅O₁₈, tunable luminescence was obtained because of the energy transfer from Ce³⁺ to Mn²⁺. In Mg₂Al₄Si₅O₁₈:Ce³⁺/Mn²⁺ phosphors with a fixed Ce³⁺ concentration, energy transfer efficiency increases with the increasing Mn²⁺ concentration, which is confirmed by the continually decreasing intensity and shortening decay time of Ce³⁺ emission. Moreover, the luminescent properties and thermal stability provide a great significance on the applications in the field of light emitting diodes.     

Persistent luminescence of Zn<Subscript>2</Subscript>GeO<Subscript>4</Subscript>:Mn<Superscript>2+</Superscript>/Pr<Superscript>3+</Superscript> phosphors

Zn₂GeO₄, Zn₂GeO₄:Mn²⁺, Zn₂GeO₄:Pr³⁺ and Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphors were fabricated by a solid state reaction. The phase and luminescent properties of the fabricated phosphors were investigated. The XRD patterns show that all of the fabricated phosphors have an orthorhombic structure. The fabricated Zn₂GeO₄ shows an emission band in the range of 350–550 nm. The fabricated Zn₂GeO₄:Mn²⁺ and Zn₂GeO₄:Pr³⁺ phosphors show emission bands corresponding to Mn²⁺ and Pr³⁺ ions, respectively. The fabricated Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphor shows the emission band results from Mn²⁺ and the codoped Pr³⁺ enhances the emission intensity of Mn²⁺. Moreover, Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphor exhibits longer decay time than that of Zn₂GeO₄:Mn²⁺. The higher intensity and longer lifetime of Mn²⁺ emission are induced by the energy transfer from Pr³⁺ of various vacancies to Mn²⁺ in Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphors.     

Novel quantum dots: Water-based CdTeSe/ZnS and YAG hybrid phosphor for white light-emitting diodes

Novel water-based core/shell CdTeSe/ZnS quantum dots (QDs) were synthesized by aqueous method. The CdTeSe/ZnS QDs were investigated by high resolution transmission electron microscopy, energy dispersive spectrometry, UV–vis absorption spectra, and photoluminescence spectrum. The as-prepared QDs capped with ZnS shell were spherical in shape with an excellent quantum yield of 16% and emitted bright yellow light. In addition, the CdTeSe/ZnS QDs can be excited by blue or near-UV region, which is an advantage over wavelength converters for white light-emitting diodes (LEDs). White LEDs based on CdTeSe/ZnS QDs, commercially known as Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce), and hybrid phosphor of CdTeSe/ZnS QDs and YAG:Ce, were fabricated. The luminescent properties of the resultant white LEDs were evaluated. The higher red-component in the emission spectrum from CdTeSe/ZnS QDs increased the color rendering index (CRI) value of the commercial YAG:Ce-based white LEDs, and the hybrid phosphor-based white LED had CIE-1993 color coordinate, color temperature, and CRI values of (0.3125, 0.2806), 7108 K and 83.3, respectively.     

Single phased Sr<Subscript>3</Subscript>La(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>:Eu<Superscript>2+</Superscript>/Mn<Superscript>2+</Superscript> phosphors: solid state synthesis,tunable luminescence and potential applications in white light LEDs

A series of Sr₃La(PO₄)₃:Eu²⁺/Mn²⁺ phosphors were synthesized by a solid state reaction. The phase and the optical properties of the synthesized phosphors were investigated. The XRD results indicate that the doped Eu²⁺ and Mn²⁺ ions do not change the phase of Sr₃La(PO₄)₃. The peak wavelengths of Eu²⁺ single doped and Eu²⁺/Mn²⁺ codoped Sr₃La(PO₄)₃ phosphors shift to longer wavelength due to the larger crystal field splitting for Eu²⁺ and Mn²⁺. The increases of crystal field splitting for Eu²⁺ and Mn²⁺ are induced by the substitution of Sr²⁺ by Eu²⁺ and Mn²⁺ in Sr₃La(PO₄)₃ host. Due to energy transfer from Eu²⁺ to Mn²⁺ in Sr₃La(PO₄)₃:Eu²⁺/Mn²⁺ phosphors, tunable luminescence was obtained by changing the concentration of Mn²⁺. And the white light was emitted by Sr₃La(PO₄)₃:3.0 mol%Eu²⁺/4.0 mol%Mn²⁺ and Sr₃La(PO₄)₃:3.0 mol%Eu²⁺/5.0 mol%Mn²⁺ phosphors.     

Influence of isovalent and heterovalent substitution for Bi<Superscript>3+</Superscript> and Fe<Superscript>3+</Superscript> on the properties of Bi<Subscript>2</Subscript>Fe<Subscript>4</Subscript>O<Subscript>9</Subscript>-based solid solutions

Bi_2–хLa_хFe₄O₉ and Bi₂Fe_4–2xTi_xCo_xO₉ ferrites have been prepared by solid-state reactions at a temperature of 1073 K. X-ray diffraction data indicate that, in the Bi_2–хLa_хFe₄O₉ system, the limiting degree of La³⁺ substitution for Bi³⁺ ions in Bi₂Fe₄O₉ does not exceed 0.05 and that the limiting degree of substitution in the Bi₂Fe_4–2xTi_xCo_xO₉ system lies in the range 0.05 < x < 0.1. The specific magnetization and specific magnetic susceptibility of the samples have been measured at temperatures from 5 to 300 K in a magnetic field of 0.86 T. The field dependences of magnetization obtained for the Bi_2–хLa_хFe₄O₉ and Bi₂Fe_4–2xTi_xCo_xO₉ ferrites at temperatures of 300 and 5 K demonstrate that partial isovalent substitution of La³⁺ for Bi³⁺ ions in Bi₂Fe₄O₉ and heterovalent substitution of Ti⁴⁺ and Co²⁺ ions for two Fe³⁺ ions leads to partial breakdown of the antiferromagnetic state and nucleation of a ferromagnetic state.     

Nano-domain structure of Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript> spinel

XRD-pure Li₄Mn₅O₁₂ spinels are obtained below 600 °C from oxalate and acetate precursors. The morphology consists of nanometric particles (about 25 nm) with a narrow particle size distribution. HRTEM and electron paramagnetic resonance (EPR) spectroscopy of Mn⁴⁺ are employed for local structure analysis. The HRTEM images recorded on nano-domains in Li₄Mn₅O₁₂ reveal its complex structure. HRTEM shows one-dimensional structure images, which are compatible with the (111) plane of the cubic spinel structure and the (001) plane of monoclinic Li₂MnO₃. For Li₄Mn₅O₁₂ compositions annealed between 400 and 800 °C, EPR spectroscopy shows the appearance of two types of Mn⁴⁺ ions having different metal environments: (i) Mn⁴⁺ ions surrounded by Li⁺ and Mn⁴⁺ and (ii) Mn⁴⁺ ions in Mn⁴⁺-rich environment. The composition of the Li⁺, Mn⁴⁺-shell around Mn⁴⁺ mimics the local environment of Mn⁴⁺ in monoclinic Li₂MnO₃, while the Mn⁴⁺-rich environment is related with that of the spinel phase. The structure of XRD-pure Li₄Mn₅O₁₂ comprises nano-domains with a Li₂MnO₃-like and a Li_4/3−x Mn_5/3+x O₄ composition rather than a single spinel phase with Li in tetrahedral and Li_1/3Mn_5/3 in octahedral spinel sites. The annealing of Li₄Mn₅O₁₂ at temperature higher than 600 °C leads to its decomposition into monoclinic Li₂MnO₃ and spinel Li_4/3−x Mn_5/3+x O₄.     

Enhanced Luminescence of Quantum Dots near a Layer of Ag/SiO<Subscript>2</Subscript> Nanoparticles

We have studied the influence of monodisperse Ag/SiO₂ core–shell-type nanoparticles with a core diameter of 17 nm and a dielectric-shell thickness within 0–40 nm on the photoluminescence of CdSe/ZnS quantum dots (QDs) excited by laser at a wavelength corresponding to the plasmon resonance in Ag/SiO₂ nanoparticles. It is established that the intensity of QD luminescence in the composite system exhibits up to 8.7-fold increase.     

Synthesis and thermoluminescence properties of CdB<Subscript>4</Subscript>O<Subscript>7</Subscript>:Tb<Superscript>3+</Superscript> and CdB<Subscript>4</Subscript>O<Subscript>7</Subscript>:Mn<Superscript>2+</Superscript>

Polycrystalline samples of undoped, terbium-doped (CdB₄O₇:Tb³⁺), and manganese-doped (CdB₄O₇:Mn²⁺) cadmium tetraborate have been prepared by solid-state reactions at 850°C. Using differential scanning calorimetry and X-ray diffraction, we have determined the melting point of CdB₄O₇ (t _m = 976°C) and shown that this compound melts incongruently. The observed monotonic decrease in the orthorhombic cell parameters of the doped materials indicates the formation of substitutional solid solutions (sp. gr. Pbca). The thermoluminescence intensity of the doped materials has been shown to depend on the nature and concentration of the activators and the irradiation time.     

Structure and luminescent properties of Cs<Subscript>2</Subscript>Sr(VO<Subscript>3</Subscript>)<Subscript>4</Subscript>:Mn<Superscript>2+</Superscript>

We have developed a procedure for thermally stimulated synthesis of a cesium strontium metavanadate, Cs₂Sr(VO₃)₄:Mn²⁺ (0.01, 0.50, 1.00, 5.00 at % Mn²⁺), using MnO-containing starting mixtures. The EPR spectrum of the material containing 0.01 at % Mn²⁺ shows a hyperfine structure due to the incorporation of a small amount of manganese into the diamagnetic double metavanadate host. The luminescent and optical properties of Cs₂Sr(VO₃)₄:Mn²⁺ depend on manganese content. In contrast to higher doping levels, doping with 0.01 at % Mn²⁺ increases the integrated emission intensity of the vanadate by 10% and improves its chromaticity characteristics (approaching them to those of white light). We assume that this is due to the reduction in the density of vacancy-type growth defects, such as oxygen vacancies.     

Influence of Mn<Superscript>2+</Superscript> on the up-conversion emission performance of Mn<Superscript>2+</Superscript>, Yb<Superscript>3+</Superscript>, Er<Superscript>3+</Superscript>: ZnWO<Subscript>4</Subscript> green phosphors

The Mn²⁺, Yb³⁺, Er³⁺: ZnWO₄ green phosphors are synthesized successfully through the high temperature solid state reaction method. The micro-structure and morphology have been investigated by means of XRD and EDS. The doped concentrations of Mn²⁺, Yb³⁺, Er³⁺ are measured by ICP. The absorption spectra and emission spectra with different doped concentrations of Mn²⁺ are presented to reveal the influence of Mn²⁺ on the green up-conversion performance. Excited with 970 nm LED, the up-conversion emission peak at 547 nm is obtained and the CIE spectra as well as the green light photo are also presented. The results indicate that the Mn²⁺ ions play the role of the luminescence adjustment in the up-conversion process, which can improve the up-conversion green emission intensity effectively. The luminescence adjustment mechanism of Mn²⁺ ions in Mn²⁺, Yb³⁺, Er³⁺: ZnWO₄ green phosphors has been discussed. The crystal parameters of Dq, B and C are calculated to evaluate the energy level split effect.     

Doping effects of Mn<Superscript>2+</Superscript> on the dielectric properties of glass-doped BaTiO<Subscript>3</Subscript>-based X8R materials

In this paper, Mn²⁺ and calcium borosilicate glass (CBS) were used as effective dopants to prepare environmentally friendly dielectric materials satisfying EIA X8R specification. The effects of various Mn²⁺ concentrations on the dielectric properties of BaTiO₃ (BT) ceramics were investigated when CBS amount was fixed. The dielectric measurements showed that the permittivity was decreased continuously with increasing Mn²⁺ concentrations, resulted from the existence of paraelectric regions caused by Mn²⁺ doping. The dielectric loss was decreased at the beginning and then increased with increasing Mn²⁺ concentrations, whereas the resistivity showed an opposite movement. The SEM images and X-ray diffraction curves corresponding to BT ceramics doped with different Mn²⁺ amounts proved that Mn²⁺ can promote the crystallization of CBS glass to form the secondary phase Ca₄Mn₄Si₈O₂₄, which determines the intensity of the high temperature peak (at about 125 °C) of the variation rate curve of capacitance. Moreover, the modification effects of Mn²⁺ on the dielectric properties of BT have been investigated. It is revealed that a proper usage of Mn²⁺ can improve the dielectric properties significantly, and Mn²⁺ and CBS co-doped BT ceramics are promising to develop X8R MLCs.     

Magnetically separable Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@TiO<Subscript>2</Subscript> nanospheres: preparation and photocatalytic activity

A facile and efficient approach for the fabrication of Fe₃O₄@TiO₂ nanospheres with a good core–shell structure has been demonstrated. Products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results showed that Fe₃O₄@TiO₂ nanocomposites exhibited high degree of crystallinity, excellent magnetic properties at room temperature. Furthermore, the as-prepared Fe₃O₄@TiO₂ nanocomposites exhibited good photocatalytic activity toward the degradation of Rhodamine B (RhB) solution. Additionally, the recycling experiment of Fe₃O₄@TiO₂ nanocomposites had been done, demonstrating that Fe₃O₄@TiO₂ nanocomposites have high efficiency and stability.     

Synthesis and applications of fluorescent-magnetic-bifunctional dansylated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanoparticles

Bifunctional magnetic-luminescent dansylated Fe₃O₄@SiO₂ (Fe₃O₄@SiO₂-DNS) nanoparticles were fabricated by the nucleophilic substitution of dansyl chloride with primary amines of aminosilane-modified Fe₃O₄@SiO₂ core–shell nanostructures. The morphology and properties of the resultant Fe₃O₄@SiO₂-DNS nanoparticles were investigated by transmission electron microscopy, FT–IR spectra, UV–vis spectra, photoluminescence spectra, and vibrating sample magnetometry. The Fe₃O₄@SiO₂-DNS nanocomposites exhibit superparamagnetic behavior at room temperature, and can emit strong green light under the excitation of UV light. They show very low cytotoxicity against HeLa cells and negligible hemolysis activity. The T ₂ relaxivity of Fe₃O₄@SiO₂-DNS in water was determined to be 114.6 Fe mM⁻¹ s⁻¹. Magnetic resonance (MR) imaging analysis coupled with confocal microscopy shows that Fe₃O₄@SiO₂-DNS can be uptaken by the cancer cells effectively. All these positive attributes make Fe₃O₄@SiO₂-DNS a promising candidate for both MR and fluorescent imaging applications.     

Morphology and luminescent properties of Al<Superscript>3+</Superscript>/Mg<Superscript>2+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphor

Al³⁺/Mg²⁺ doped Y₂O₃:Eu phosphor was synthesized by the glycine-nitrate solution combustion method. In contrast to Y₂O₃:Eu which showed an irregular shape of agglomerated particles (the mean particle size >10 μm), the morphology of Al³⁺/Mg²⁺ doped Y₂O₃:Eu crystals was quite regular. Al³⁺/Mg²⁺ substituting Y³⁺ in Y₂O₃:Eu resulted in an obvious decrease of the particle size. Meanwhile, higher the Al³⁺/Mg²⁺ concentration, smaller the particle size. In particular, the introduction of Al³⁺ ion into Y₂O₃ lattice induced a remarkable increase of PL and CL intensity. While, for Mg²⁺ doped Y₂O₃:Eu samples, their PL and CL intensities decreased. The reason that causes the variation of PL and CL properties for Al³⁺ and Mg²⁺ doped Y₂O₃:Eu crystals was concluded to be related to sites of Al³⁺ and Mg²⁺ ions inclined to take and the difference of ion charge.     

The Multiferroic Properties of (Bi<Subscript>0.9</Subscript>Ba<Subscript>0.1</Subscript>)(Fe<Subscript>0.95</Subscript>Mn<Subscript>0.05</Subscript>)O<Subscript>3</Subscript> Films

(Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ films were prepared on LaNiO₃-coated surface oxidized Si substrates. XRD and Raman measurements confirm that the (Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ film has pure R3c structure. Clear ferromagnetism with saturated magnetization of about 25 emu/cm³ has been observed at room temperature. The ferroelectric properties of the (Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ film was confirmed by the observation of the ferroelectric domains and the converse piezoelectric coefficient d ₃₃ versus applied voltage hysteresis loops by piezoelectric force microscopy (PFM). The observation of ferromagnetism and ferroelectricity in (Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ films indicates the potential multiferroic applications.