Synthesis of NaYF4:Yb3+, Er3+ upconversion nanoparticles in normal microemulsions

An interface-controlled reaction in normal microemulsions (water/ethanol/sodium oleate/oleic acid/n-hexane) was designed to prepare NaYF4:Yb3+, Er3+ upconversion nanoparticles. The phase diagram of the system was first studied to obtain the appropriate oil-in-water microemulsions. Transmission electron microscopy and X-ray powder diffractometer measurements revealed that the as-prepared nanoparticles were spherical, monodisperse with a uniform size of 20 nm, and of cubic phase with good crystallinity. Furthermore, these nanoparticles have good dispersibility in nonpolar organic solvents and exhibit visible upconversion luminescence of orange color under continuous excitation at 980 nm. Then, a thermal treatment for the products was found to enhance the luminescence intensity. In addition, because of its inherent merit in high yielding and being economical, this synthetic method could be utilized for preparation of the UCNPs on a large scale.     

Composition tuning the upconversion emission in NaYF4:Yb/Tm hexaplate nanocrystals

Single crystal hexagonal NaYF4:Yb/Tm nanocrystals have been synthesized with uniform size, morphology and controlled chemical composition. Spectroscopic studies show that these nanocrystals exhibit strong energy upconversion emission when excited with a 980 nm diode laser, with two primary emission peaks centered around 452 nm and 476 nm. Importantly, the overall and relative emission intensity at these wavelengths can be readily tuned by controlling the concentration of the trivalent rare earth element dopants at the beginning of the synthesis which has been confirmed by EDX for the first time. Through systematic studies, the optimum rare earth ion doping concentration can be determined for the strongest emission intensity at the selected peak(s). Confocal microscopy studies show that the upconversion emission from individual NCs can be readily visualized. These studies demonstrate a rational approach for fine tuning the upconversion properties in rare-earth doped nanostructures and can broadly impact areas ranging from energy harvesting, energy conversion to biomedical imaging and therapeutics.     

NaYF4:Yb/Tm上转换荧光材料的制备及发光性质研究

文章采用水热法制备了PEI修饰的上转换荧光纳米晶NaYF4:Yb/Tm。XRD和TEM测试表明,产物具有良好的结晶性,其形貌为球状,平均粒径为20 nm。在980 nm光源激发下,随着Tm或Yb掺杂浓度的增大,纳米晶的上转换发光强度逐渐减弱。从能级跃迁的角度分析发现,纳米晶在不同Yb/Tm掺杂量的上转换发光性质变化主要受浓度猝灭和Tm的1D2和1G4能级布居两方面影响。     

稀土上转换发光材料NaYF4:Yb:Er的合成研究

在NaYF4基质中掺杂Y3 和Er3 ,合成了上转换材料NaYF4:Yb:Er,并对所得到的产物进行了表征.探讨了在合成NaYF4:Yb:Er过程中,Yb和Er的掺杂浓度、溶液的酸度、活化的温度等因素对形成六方相NaYF4:Yb:Er的影响.     

九种M~(2+)掺杂对NaYF_4:Yb,Er上转换红光的影响研究

本文通过水热法合成不同浓度M~(2+)掺杂的NaYF_4:18%Yb~(3+),2%Er~(3+)上转换发光材料。系统的探讨了九种二价金属离子掺杂以及不同掺杂浓度对材料的上转换红光强度的影响。利用扫描电子显微镜(SEM)、X射线衍射分析(XRD)、荧光光谱等测量手段对样品进行了形貌、晶相、发光性质的表征。2%掺杂浓度下全部离子对上转换发光均稍有增强;5%掺杂浓度下,Sr、Ca对上转换荧光的增强效果最为显著,Ni、Zn、Co稍有增强,而Mg、Cu、Mn、Ba均降低了发光;10%掺杂浓度下,Mg、Ca对上转换荧光的增强效果最为显著,Zn稍有增强,而Ni、Sr、Cu、Mn、Ba、Co均降低了发光。荧光光谱结果表明碱土金属掺杂对发光的增强效果优于过渡金属掺杂,过渡金属对材料形貌的改善效果优于碱土金属。二价金属离子对红光的增强效果明显优于绿光。     

Power dependent upconversion in Er3+/Yb3+ co-doped BiNbO4 phosphors

In the present article, optical properties and energy upconversion in Er³⁺/Yb³⁺ co-doped BiNbO₄ matrix were investigated. The BiNbO₄ matrix was prepared using the solid-state reaction method. X-ray diffraction of the matrix shows that the crystal structure is consistent with ICSD code 74338. The grain distribution and the behavior of doping with Er³⁺ and Yb³⁺ on the sample surface were obtained by scanning electron microscope. Raman spectral characterization was carried out to examine the behavior of the vibrational modes of the samples. Upconversion emissions in the visible region at 484.5, 522, 541.5 and 670.5 nm in the matrices BiNbO₄:Er,Yb and BiNbO₄:Er were observed and analyzed as a function of 980 nm laser excitation power and rare-earth doping concentration. The results show that BiNbO₄ is a promising host material for efficient upconversion phosphors.     

Upconversion of NaYF4: Yb,Er Nanoparticles Co-doped with Zr 4+ for Magnetic Phase Transition and Biomedical Imaging Applications

Tracking of cancer cells and cytotoxicity of normal tissue are the leading problem in cancer treatment. The magnetic and fluorescent multifunctional particles evolve as an emerging alternative for future target recognition. The ferromagnetic materials potentially treat the defects in the gene. Hence, ferromagnetic materials are the best for the treatment of cancer using gene therapy. Here, β-NaYF₄: Yb, Er compounds doped with 10%, 20% and 30% Zirconium (Zr) are prepared through hydrothermal technique. Citrate itself is a highly biocompatible surface ligand that labels the imaging probe. The X-ray diffraction analysis is evident for transforming hexagonal to cubic phase via Zr doping in NaYF₄: Yb, Er compounds. The electron microscopic images identify the hexagonal plates. This compound can emit visible light in response to infrared (IR) light irradiation. Especially β-NaYF₄: Yb, Er, and 10% of Zr, Yb, Er tridoped NaYF₄ compounds show enhanced red emission exploited in bioimaging applications. Insignificantly, 30% of Zr, Yb, Er tridoped NaYF₄ concentration exhibit hexagonal and dominating cubic (α) phase, could decrease red emissions intensity and magnetisation value. This Zr material reveals peculiar magnetic properties, especially ferromagnetism at a lower magnetic field and produces paramagnetism at a higher magnetic field. Here, 10–20% Zr, Yb, Er tridoped NaYF₄ concentrations exhibit better magnetic properties. The resultant compound is viable for the VERO cells.

     

Plasmon enhanced upconversion luminescence of NaYF(4):Yb,Er@SiO(2)@Ag core-shell nanocomposites for cell imaging

NaYF(4):Yb,Er@SiO(2)@Ag core-shell nanocomposites were prepared to investigate metal-enhanced upconversion luminescence. Two sizes (15 and 30 nm) of Ag nanoparticles were used. The emission intensity of the upconversion nanocrystals was found to be strongly modulated by the presence of Ag nanoparticles (NPs) on the outer shell layer of the nanocomposites. The extent of modulation depended on the separation distance between Ag NPs and upconversion nanocrystals. The optimum upconversion luminescence enhancement was observed at a separation distance of 10 nm for Ag NPs with two different sizes (15 and 30 nm). A maximum upconversion luminescence enhancement of 14.4-fold was observed when 15 nm Ag nanoparticles were used and 10.8-fold was observed when 30 nm Ag NPs were used. The separation distance dependent emission intensity is ascribed to the competition between energy transfer and enhanced radiative decay rates. The biocompatibility of the nanocomposites was significantly improved by surface modification with DNA. The biological imaging capabilities of these nanocomposites were demonstrated using B16F0 cells.     

Dual-modal fluorescent/magnetic bioprobes based on small sized upconversion nanoparticles of amine-functionalized BaGdF5:Yb/Er

A new type of BaGdF(5):Yb/Er nanoprobe for dual-modal fluorescent and magnetic resonance imaging (MRI) is demonstrated. Water soluble and amine-functionalized BaGdF(5):Yb/Er nanoparticles (NPs) with average size of about 10 nm were synthesized by a facile one-pot hydrothermal method. The in vitro up-converted emission of BaGdF(5):Yb/Er NPs is observed in HeLa cells with near-infrared excitation at 980 nm and served as a fluorescent label. In addition, the cytotoxicity assay in HeLa cells shows low cell toxicity of the amine-functionalized BaGdF(5):Yb/Er NPs. Moreover, these BaGdF(5) NPs exhibit excellent intrinsic paramagnetic properties and enhanced T(1)-weighted MRI images with increased concentrations of BaGdF(5) NPs. Therefore, these results suggest that the amine-functionalized BaGdF(5) NPs with an optimized size and low cell toxicity are promising dual-modal bioprobes for optical bioimaging and MRI.     

Visible green upconversion luminescence of Er3+/Yb3+/Li+ co-doped CaWO4 particles

The upconversion (UC) luminescence of Li⁺/Er³⁺/Yb³⁺ co-doped CaWO₄ phosphors is investigated in detail. Single crystallized CaWO₄:Li⁺/Er³⁺/Yb³⁺ phosphor can be obtained, co-doped up to 25.0/5.0/20.0 mol% (Li⁺/Er³⁺/Yb³⁺) by solid-state reaction. Under 980 nm excitation, CaWO₄:Li⁺/Er³⁺/Yb³⁺ phosphor exhibited strong green UC emissions visible to the naked eye at 530 and 550 nm induced by the intra-4f transitions of Er³⁺ (²H_11/2,⁴S_3/2→⁴I_15/2). The optimum doping concentrations of Yb³⁺/Li⁺ for the highest UC luminescence were verified to be 10/15 mol%, and a possible UC mechanism that depends on the pumping power is discussed in detail.     

水热法制备的六方相NaYF4:Er3+,Dy3+荧光粉的吸收光谱

用水热法制备了六方相NaYF4:Er3+,Dy3+荧光粉.通过在NaYF4:Er3+中共掺Dy3+,拓宽上转换荧光粉的吸收峰,以增加太阳能电池在红外光谱区的吸收范围.通过X射线衍射和分光光度计检测和分析了共掺Dy3+对荧光粉的晶体结构和晶格缺陷的影响以及拓宽荧光粉在红外光谱区的吸收范围.结果表明:共掺Dy3+后,晶胞产...     

Enhanced upconversion emission in Yb3+ and Er3+ codoped NaGdF4 nanocrystals by introducing Li+ ions

β-NaGdF(4)?:?Yb(3+)/Er(3+) nanoparticles (NPs) codoped with Li(+) ions were prepared for the first time via a thermal decomposition reaction of trifluoroacetates in oleylamine. The influence of site occupancy of Li(+) on the upconversion emission of β-NaGdF(4)?:?Yb(3+)/Er(3+) NPs was investigated in detail. The upconversion emission intensity was significantly enhanced by introducing different concentrations of Li(+) ions. In contrast to lithium-free β-NaGdF(4)?:?Yb(3+)/Er(3+), the green and red UC emission intensities of the NPs codoped with 7 mol% Li(+) ions were enhanced by about 47 and 23 times, respectively. The luminescence enhancement should be attributed to the distortion of the local asymmetry around Er(3+) ions. The mechanisms for the enhancement of upconversion emission were discussed. In addition, it was found in our research work that β-NaGdF(4)?:?Yb(3+)/Er(3+) NPs exhibited paramagnetic features at room temperature and the magnetization was slightly increased by introducing Li(+) ions.     

Monodisperse upconversion GdF<Subscript>3</Subscript>:Yb,Er rhombi by microwave-assisted synthesis

We have synthesized a variety of monodisperse colloidal GdF₃:Yb, Er upconversion nanocrystals with different shape, size, and dopants by microwave-assisted synthesis. Typical upconversion emission from Er³⁺ was observed. In addition to highly monodisperse spherical particles, we were able to prepare monodispersed rhombic-shaped slices that showed a tendency for self-assembly into stacks.     

La2O2SO4:RE/Yb new phosphors for near infrared to visible and near infrared upconversion luminescence (RE=Ho,Er, Tm)

The 3 new upconversion (UC) phosphors of La₂O₂SO₄:RE/Yb (RE=Ho, Er, and Tm, respectively) were derived via facile dehydration of their layered hydroxide precursors that were hydrothermally synthesized at 100°C. Rietveld XRD refinement found contracting cell dimension with decreasing RE³⁺ size, confirming the direct crystallization of solid solution. The Er³⁺ and Ho³⁺ activators both exhibited simultaneous green and red (dominant) emissions under 978‐nm near‐infrared (NIR) laser excitation (NIR‐Vis UC). Particularly, Tm³⁺ produced a Gaussian‐shaped pure NIR emission band at ~812 nm via its ³H₄ → ³H₆ transition (NIR‐NIR UC), which is highly desired for NIR biological application. Analysis of the excitation‐power dependent UC properties manifested a 3‐photon mechanism for the 3 phosphors, and the possible photon reactions leading to UC were illustrated.     

Thermal effects of Er3+/Yb3+‐doped NaYF4 phosphor induced by 980/1510 nm laser diode irradiation

The thermal effects of Er/Yb‐doped NaYF₄ phosphor induced by 980/1510 nm laser diode irradiation were intuitively and contrastively investigated using an infrared thermal imaging technology with real‐time online monitoring. The Yb³⁺/Er³⁺ codoped materials have strong thermal effects and high‐temperature elevation under 980 nm irradiation. However, the severe thermal effects of materials with higher Er³⁺ ion doping concentration are remarkably attributed to the cross relaxation between the Er³⁺ ions under 980 nm irradiation. The energy transfer between Er³⁺ and Yb³⁺ ions in Er³⁺/Yb³⁺‐codoped materials also contributes to the thermal effects under 1510 nm laser diode irradiation. Under the same testing conditions, the temperature elevation ?T of samples induced by 1510 nm laser diode irradiation is lower than that induced by 980 nm laser diode irradiation. The temperature rising rate and elevation ?T value of samples depend on the ion doping concentration and power density of the laser diode excitation. The internal temperature of the samples exhibits deep temperature gradient under 980/1510 nm laser diode irradiation. By comparing the two kinds of thermometry methods, the temperature value calculated by fluorescence intensity ratio is almost similar to that obtained through infrared thermal imaging technology under higher excitation power pumping.     

NaYF4:Yb,Tm与CdS量子点协同提高二氧化钛光催化性能

上转换材料可将低能红外光转换为高能可见光或紫外光,而量子点敏化可调节TiO_2的能带宽度。本实验首先合成nc-TiO_2纳米晶胶体,制成nc-TiO_2膜,再进行Cd S量子点敏化,与制得的NaYF_4:Yb,Tm进行复合。对所得的CdSQDs/TiO_2/NaYF_4:Yb,Tm复合膜采用TEM和XRD,以及上转换荧光表征,并借用探针反应,测试膜的光催化活性。结果表明在全光照射下,Cd S QDs/TiO_2和TiO_2/NaYF_4:Yb,Tm及Cd S QDs/TiO_2/NaYF_4:Yb,Tm复合膜的光催化降解速率分别是TiO_2的1. 8,1. 4和2. 6倍,说明NaYF_4:Yb,Tm与量子点可协同提高二氧化钛全波段光催化性能。     

Near‐UV activated,photostable nanophosphors for in vitro dosimetry and dynamic bioimaging

Luminescent rare earth nanoparticles exhibit superior optical stability over commonly‐used organic dyes and higher biocompatibility over quantum dots, rendering them advantageous as bioimaging nanoprobes. However, their typical excitation inhibits their broad employment with conventional fluorescence microscopes and, thus, solutions are sought to shift their activation in the long‐wavelength (near‐UV) spectral region. Here, we synthesize YVO₄:Eu³⁺ nanophosphors by flame aerosol technology to systematically study the effect of Bi³⁺ codoping on their luminescence. That way, we identify an optimal Bi‐content for sufficient near‐UV activation. These nanophosphors are highly crystalline and appeared bright red under a conventional fluorescence microscope, facilitating bioimaging with HeLa cells and in vitro dosimetry correlations in the presence and absence of serum. The nanophosphor superiority over organic‐dye‐labeled silica nanoparticles is shown during dynamic imaging for 4 h without photobleaching for the former. These YVO₄:Eu³⁺/Bi³⁺ nanophosphors can provide a non‐photobleaching tool for further dynamic nanoparticle‐cell interaction studies with conventional fluorescence microscopes. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2947–2957, 2018     

High-sensitivity in vivo imaging for tumors using a spectral up-conversion nanoparticle NaYF4: Yb3+, Er3+ in cooperation with a microtubulin inhibitor

Fluorescein has been used for in vivo imaging to identify tumors. However, this technique presents several limitations, mainly due to its limited targeting efficiency, tissue autofluorescence and poor light penetration in tissue. In the present study, an alternative fluorescence imaging technique to localize tumors has been developed by using up-conversion nanoparticles (UCNs) and enhanced targeting approaches. A folic acid molecule is conjoined with UCNs (NaYF(4): Yb(3+), Er(3+)) to improve the tumor-specificity; the UCN is also loaded with the microtubule inhibitor CA4P, to further improve the local delivery of particles in the tumor. The proposed imaging technique combines several well-established individual concepts into one novel integrated procedure and significantly improves its tumor-imaging capability: the near-infrared excitation for UCNs minimizes tissue autofluorescence and allows imaging into deeper tissue; the improvement in the signal to noise ratio (SNR) is at least a magnitude better than that of a conventional fluorescence imaging technique, and the modification of UCNs with folic acid significantly improves the tumor targeting efficiency by utilizing its affinity for the folic acid receptor that is often over expressed in tumors. The loading of CA4P further helps UCNs to cross blood vessel walls to reach tumor cells by depolymerizing the microtubules of endothelial cells. The integrated nanoparticle possesses the near-infrared-identical optical properties of UCNs alone, thus achieving a highly effective fluorescence imaging probe. The results demonstrated that the proposed method provides an excellent alternative for tumor localization and a potential traceable vehicle for highly efficient drug delivery.     

Water-soluble,mesoporous Fe3O4: Synthesis,characterization, and properties

Water-soluble, mesoporous Fe₃O₄ nanopowder is successfully prepared by one-step thermal decomposition of an iron-urea complex ([Fe(NH₂CONH₂)₆](NO₃)₃) in triethylene glycol (TEG). The formation of Fe₃O₄ is confirmed from X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and selected area electron diffraction (SAED) measurements. The morphological and structural properties of the Fe₃O₄ nanopowder are characterized by transmission electron microscopy (TEM), nitrogen adsorption–desorption, and thermogravimetric analysis (TGA). Monodisperse, nearly spherical and highly crystalline Fe₃O₄ nanoparticles are obtained by this method. The Fe₃O₄ nanopowder is well dispersed in water and ethanol with a mesoporous structure, average pore size of 3.6 nm, and Brunauner–Emmett–Teller (BET) surface area of 122 m²/g. The room temperature magnetization hysteresis curve exhibits barely measurable values for coercivity and remanence, suggesting that the Fe₃O₄ nanopowder possesses superparamagnetic characteristics.     

Upconversion luminescence enhancement of NaYF4:Yb3+,Er3+ nanocrystals induced by the surface plasmon resonance of nonstoichiometric WO2.72 semiconductor

Upconversion luminescence of rare‐earth ions doped nanoparticles can be enhanced by the localized surface plasmon resonance (LSPR) of noble metals nanoparticles, which was extensively investigated. The semiconductor nanomaterials such as the WO_2.72 exhibited the tunable LSPR, which provide the possibility for the luminescence enhancement of upconversion nanoparticles. In this work, the urchin‐like WO_2.72 was successfully prepared by solvothermal method, exhibiting the LSPR in the near infrared region. The influence of LSPR of WO_2.72 on the upconversion luminescence of NaYF₄:Yb³⁺,Er³⁺ nanoparticles was investigated firstly. The 525, 542, and 660 nm upconversion luminescence of NaYF₄: Yb³⁺,Er³⁺ nanoparticles was increased by the 10, 8, and 12 factors, respectively, which was from the enhanced excitation field induced by the WO_2.72 film.