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Paper Reading Notes

These are my science paper reading notes, the format of reading note is:

Title of the paper or article

  • Paper/article's other information（Reference information），such as authors, journal，publication date and so on.

Text：reading notes for this paper/article or summary of this paper/article.

And I should make a explain for it(paper reading note). I take this note in order to improve my English / Research ability. According to the professor Peter W. Carr 's video for reading papers, my notes are wrote after surveying and reading articles.

For "Surveying the articles", the keys are reading the title and keywords & reading the abstract & reading the conclusions.

For "Reading the articles", the keys are looking at the tables and figures & reading the introduction & reading the results and discussion & reading the experimental

Other tips: select papers which are published in last 5 years, get some information from the references of these papers and focus on top researchers' works.

Plasmonic Chemmistry

Strong coupling between magnetic resonance and propagating surface plasmons at visible light frequencies

  • Jingyu Wang, Weimin Yang. al, Strong coupling between magnetic resonance and propagating surface plasmons at visible light frequencies. J. Chem. Phys.152, 014702 (2020)

The conclusion of this paper is that the strong coupling in a PIMR-based platform composed of a 2D metallic nanogroove array filled with SHINs at visible frequencies was theoretically demonstrated for the first time. Analysis of these nanostructures shows that the PIMR mode can be successfully modulated in the visible region of the spectrum. With the aid of the strong coupling, a narrow linewidth mixed mode with huge electric and magnetic field enhancements was obtained.

Based on the calculation result, for the first time, the feasibility of strong coupling between plasmon-induced magnetic resonant and propagating surface plasmonic modes at visible light frequencies is theoretically demonstrated. Taking advantage of the strong coupling between these modes allowed for a narrow-linewidth hybrid mode with a huge electromagnetic field enhancement to be acquired.

The author employed 3D-FDTD numerical method (Lumerical Solutions, Canada) to study in detail the far-field scattering and near-field distribution properties of the PIMR and PSP modes of the SHIN metamaterial whose structure consists of a 2D Au nanogroove array filled with SHINs. And the structural parameters of the nanogroove are width (w) = 250 nm, groove depth (h) = 250 nm, and the refractive index of the environment (n) = 1. The simulation times were set as 1000 fs to ensure convergence

Their work’s results, the found two new hybrid states and can be qualitatively represented by the Hamilto-nian coupled oscillator model, with the satisfied eigenvalue equation and based on it, the wavelength of the PSP mode of the 2D rectangular array under normal incidence can be expressed by the following equation (in this paper).

Strong Spin-Orbit Interaction of Light in Plasmonic Nanostructures and Nanocircuits

  • Deng Pan, Hong Wei, Long Gao, and Hongxing Xu. Phys. Rev. Lett. 117, 166803 – Published 12 October 2016

When light interacts with a medium, the conservation of optical angular momentum (AM) can lead to a coupling between the photons’ intrinsic spin degree of freedom and their orbital motion.An example manifestation of this spin orbit interaction (SOI) of light is the transverse shift of circularly polarized beams when reflected by a dielectric interface. In this letter, authors tackled both of these issues: although studies have, in principle,demonstrated the utilization of SOI for plasmonic devices, promising applications of the spin degree of freedomfor optical information in plasmonics depend on the loadingand sorting of circularly polarized photons in interconnectedcompact plasmonic nanocircuits—this feature has toour knowledge not yet been realized and reported.

They shown how the SOI of light is enhanced in plasmonic metal nanostructures, and explored the underlying mechanismfor this effect, and further demonstrated how it could potentially be harnessed for nanophotonic applications. They shown that the scattering of circularly polarized photons by a single metal nanosphere causeslight to propagate along sharply twisted chiral trajectories near the nanosphere, thus revealing a strong SOI inthe near field of surface plasmons and found similar spin-dependent trajectories of light induced by a strongSOI also in the near field of surface plasmons generated on the tip of a metal nanowire.Then, utilized this strong SOI to for the first time experimentally realize spin sorting of photons in a compact plasmonic nanocircuit.The findings offer insights into how the SOI of light can be enhanced and explored for a new degree offreedom in plasmonic nanocircuits and future spin-controlled nanophotonic devices.

First step in this paper is that introduce the AM and the SOI of photons using a Dirac-like form of Maxwell’s equation, then, using finite element method (COMSOL Multiphysics software) to calculate simulation results via classical Maxwell’s equations. The theoretical studey to illustrate how this type of strong SOI of photons canbe induced in plasmonic nanostructures. According to the simulation result, The wavelength is 785 nm. Thus, they set the experiment. They xperimentally demonstrate the predicted spin-sortingfunctionality in their fabricated branched-nanowire structure

In summary, authors provided insights into howthe SOI of photons can be strongly enhanced in plasmonicnanostructures and how this effect could be used to achievenew functionalities in nanophotonic circuits. They have studied the evolution of the AM of light during theinteraction between circularly polarized photons and indi-vidual metal nanostructures, and found that light propa-gates along chiral trajectories in the near field of SPsbecause of a strong SOI. This effect can be readily used toencode, transport, and manipulate the spin degree offreedom of optical information in nanophotonic and plas-monic circuits, as demonstrated by their proof-of-principleexperiments on spin sorting in a plasmonic nanocircuit.

Calculated shape dependence of electromagneticfield in tip-enhancedRaman scattering by using a monopole antenna model

To evaluate the shape of an Ag tip with regard to tip-enhanced Raman scattering (TERS) signal, the enhanced electro magnetic (EM)field and scattering spectrum, arising from surface plasmon resonance at the apex of thetip, were calculated using afinite-difference time domain (FDTD) method. In the calculated forward scatteringspectra from the smooth Ag tip, the band appeared within the visible region, similar to the experimental resultsand calculation for a corrugated Ag cone. In the FDTD calculation of TERS, the Ag tip acting as a monopole antennawas adopted by insertion of a perfect electric conductor between the root of the tip and a top boundary surface ofthe calculation space. As a result, the EMfield was only enhanced at the apex. The shape dependence i.e. the EMfield calculated at the apex with various curvatures on the different tapered tips, obtained using the monopoleantenna model, was different from that simulated using a conventional dipole antenna.

The calculation software is EEM-FDM (EEM Inc., Saitama, Japan), to find some relationship from 300 nm to 1000nm, and their summary is that: in the calculation of enhanced EMfield for TERS, selection of themodels to be applied to the semi-infinite system is a controversialtopic. In the present study, a PEC was inserted between the root of aAg tip and a boundary surface of the calculation space. The realistic sit-uation in which the EMfield is enhanced only at the apex wasreproduced by the monopole antenna model. In the model, the EMfield wasalways calculated to beweakonthe PEC. This modelcanbeap-plied to a grating-coupling tip, because the EMfield is always en-hanced on the grating and propagates to the apex. While the forwardscattering band appeared within the visible region, as observed in theexperimental results,nosignificant difference between theSPR scattering spectra from the tip with and without the PEC was calcu-lated. On the other hand, the shape dependence of the EMfield at theapex of the tip with the PEC was different from that without the PEC.While the EMfield at the apex on the short cone of the tip withoutthe PEC was larger than that on the long cone, the opposite trend wasobserved at the apex of the tip with PEC of small curvature. It may bepossible to confirm the validity of the monopole antenna model forthe EMfield, in terms of the different shape dependence, comparedwith the dipole antenna model, by TERS and SEM measurements.

On the convergence and accuracyof the FDTD method for nanoplasmonics

  • Antonino Calà Lesina, Alessandro Vaccari, Pierre Berini, and Lora Ramunno, "On the convergence and accuracy of the FDTD method for nanoplasmonics," Opt. Express 23, 10481-10497 (2015)

I read some papers with FDTD calculation, so I checked this paper to understand it.

Use of the Finite-Difference Time-Domain (FDTD) method tomodel nanoplasmonic structures continues to rise – more than 2700 papershave been published in 2014 on FDTD simulations of surface plasmons.However, a comprehensive study on the convergence and accuracy of themethod for nanoplasmonic structures has yet to be reported. Althoughthe method may be well-established in other areas of electromagnetics,the peculiarities of nanoplasmonic problems are such that a targetedstudy on convergence and accuracy is required. In this paper, authors studied the FDTD convergence for plasmonic nanostructures considering per-componentversus uniform staircase mesh, double versus single-precision arithmetic, and dispersive Drudemodel with critical points versus standard Drude. They have seen that the per-component ap-proach guarantees a faster convergence of the FDTD algorithm for the sphere and bowtie, whilethe uniform staircase method works better for the dipole nanoantenna. Round-off errors can ap-pear with decreasing mesh size in single and double-precision simulations. The Drude model,in the range where it is valid, produces an irregular convergence with respect to the Drude+2CPmodel for both gold and silver. Faster convergence results are expected using more advancedmeshing techniques, like conformal mesh and subpixel smoothing. Future work will aim toimplement these techniques for the Drude+2CP model in 3-D for more efficient plasmonicsimulations.

One detail about their setting is that: The total simulation duration was taken to be 25 fs, which is long after the pulse has gone,in order to guarantee the steady-state regime. This corresponds to 15000 FDTD time iterationsfor the nominal simulation. The simulation volume was meshed with different space-steps: 10, 5, 2, 1, 0.5, 0.25 and0.125 nm, and for each of them the time-step was scaled accordingly. The physical simulationtime was 25 fs, resulting in 1500, 3000, 7500, 15000, 30000, 60000 and 120000 FDTD timeiterations, respectively.

Materials Chemistry

Chemical Design and Synthesis of Functionalized Probes for Imaging and Treating Tumor Hypoxia

  • Liu, J. N., Bu, W. B. , and J. L. Shi . "Chemical Design and Synthesis of Functionalized Probes for Imaging and Treating Tumor Hypoxia." Chemical Reviews 9.117(2017):6160-6224.

Hypoxia development in tumor is closely associated with its increased aggressiveness and strong resistance to therapy, leading to the poor prognosis in several cancer types. Clinically, invasive oxygen microelectrode and high dosage radiotherapy are often utilized to accurately detect and effectively fight hypoxia. Recently, however, there has been a surge of interdisciplinary research aiming at developing functional molecules and nanomaterials that can be used to noninvasively image and efficiently treat hypoxic tumors. In this review, we will provide an overview of the reports published to date on the imaging and therapy of hypoxic tumors. First, we will present the design concepts and engineering of various hypoxia-responsive probes that can be applied to image hypoxia noninvasively, in an order of fluorescent imaging, positron emission tomography, magnetic resonance imaging, and photoacoustic imaging. Then, we will summarize the up-to-date functional nanomaterials which can be used for the effective treatments of tumor hypoxia. The well-established chemical functions of these elaborately designed nanostructures will enable clinicians to adopt specific treatment concepts by overcoming or even utilizing hypoxia. Finally, challenges and future perspectives facing the researchers in the field will be discussed.

Plasmonic enhancement of lanthanides luminescence using metallic nanoparticles

  • Berthelot, A. , et al. "Plasmonic enhancement of lanthanides luminescence using metallic nanoparticles." Optical Components and Materials XI International Society for Optics and Photonics, 2014.

Lanthanides ions have been widely studied for numerous optical applications such as solar cells , optical amplification, and bio-labeling , as well as for photodynamic cancer therapy . Although they present high quantum efficiencies, they can suffer from low absorption and emission cross-sections (around 10-20 cm2) so that metal-enhanced fluorescence (MEF) has been proposed to improve their emission properties.Plasmon-enhancing excitation does not modify the emission properties of Eu3+ ions because the emission lines are too far from the plasmon resonance. In contrast, lanthanide absorptions, based on 4f transitions, are very weak (around 10-20 cm2). Therefore, the strongest enhancement is expected when matching the lanthanide absorption wavelength with the dipolar plasmon resonance. The emission of a lanthanide can be far from the excitation wavelength and still probably not influenced much by the plasmon phenomenon

Metal enhanced fluorescence in rare earth doped plasmonic core–shell nanoparticles

  • S Derom et al. "Metal enhanced fluorescence in rare earth doped plasmonic core–shell nanoparticles" Nanotechnology 24(2013):495704

Metal enhanced spectroscopies rely on excitation and/or emission enhancement by coupling emitters to a plasmonic particle. This has been extensively studied, notably for tip or surface-enhanced Raman scattering (TERS/SERS) or dye fluorescence enhancement. In practice, the highest signal enhancement is achieved for low initial absorption cross-section and quantum yield, since both the excitation and the emission processes are enhanced. Sun et al described SERS as photoluminescence enhancement in the limit of null initial absorption cross-section and quantum yield. Therefore, SERS presents the highest enhancement (up to 106) whereas MEF is typically of a few tens only. Nevertheless there sults achieved for dye molecule scan not be directly transposed to rare earth ions which present extremely low absorption cross-sections but quantum efficiencies close to unity, in contrast to dyes which present high absorption cross-sections and generally lower quantum efficiencies. In addition,it is worth while to note that lanthanide luminescence is also extremely sensitive to the surroundings so that identifying the role of plasmons is a difficult task. A large number of works, mainly experimental, but also theoretical, have been realized in order to probe the possibility to enhance the optical properties of rare earth ion splaced near metal nanoparticles .Some recent works have highlighted that gold or silver metal nanoparticles could change the selection rules of rare earth ion emission, but the localized plasmon contribution remains under discussion. Indeed, it is very difficult to separate the respective roles of plasmons and energy transfer in the observed enhancement.

In practice, the highest signal enhancement is achieved for low initial absorption cross-section and quantum yield, since both the excitation and the emission processes are enhanced. The highest plasmon mediated enhancement is achieved when the particle’s dipolar resonance matches the excitation wavelength. The enhancement mainly comes from excitation rate enhancement by coupling to the dipolar mode, whereas the emission process is weakly modified. It is also possible to enhance the excitation by coupling to the quadrupolar plasmon and the emission by coupling to the dipolar plasmon. This offers a supplementary degree of freedom for luminescence control. These results differ from dye-doped particles. Indeed, the small Stokes shift between the emission and excitation wavelengths leads then to the choice of a particle resonance overlapping the two in order to enhance both the excitation and the radiative rates by coupling to the dipolar resonance.

An organolanthanide(III) single-molecule magnet with an axial crystal-field: influence of the Raman process over the slow relaxatio

  • Long, Jér?me, et al. "An organolanthanide(III) single-molecule magnet with an axial crystal-field: influence of the Raman process over the slow relaxation." Chem. Commun. 53.34(2017):4706-4709.

Controlling the coordination environment/geometry of lanthanide ions appears as a decisive problem for the rational design of mononuclear Single-Molecule Magnets (SMMs).1 These complexes, composed solely by an unique paramagnetic ion and one or several ligand(s) exhibit a slow-relaxation of the magnetization that may eventually be associated with a magnetic bistability.2 Consequently, they can be viewed as promising candidates for future applications including information storage and data processing.3 It has been demonstrated that their slow relaxation features strongly depend on both, the nature of the lanthanide ion and the strength of the crystal field. In this line of thought, one of the recent challenges in this field consists in designing high symmetry lanthanide-based complexes possessing also large axial crystal field allowing to decrease the effect from transverse crystal-field components. This permits to suppress the rate of the Quantum Tunnelling of Magnetization (QTM), which is the main reason for reducing the SIM performances. In this sense, organometallic chemistry offers an appealing alternative to ligands involving N and O donor atoms traditionally used in coordination chemistry.

Consequently, the relaxation of the magnetisation occurs mostly via a combination of Raman and QTM processes in the considered temperature range. The QTM is known to be greatly reduced upon applying DC fields.This suggests a contribution of the QTM in the zero-field relaxation that decrease the effective energy barrier. Such discrepancy points out a certain covalency that cannot be modelled through simple electrostatic considerations

Dy-based compounds exhibit a geniune Single-Molecule Magnet (SMM) behaviour，while the Tb3+ analogue shows a field-induced slow relaxation of the magnetisation.

organometallic DAD ligands can be used to design genuine SMMs with lanthanide ions exhibiting an oblate electronic distribution, such as Dy3+. The as-obtained complexes 1a and 1b with an axial crystalfield exhibit a zero-field SMM behaviour. Remarkably, the DAD ligands are able to generate large crystal filed splitting for Dy3+ and Tb3+ ions. Nevertheless, the results indicate that the Raman relaxation has to be minimized to optimize the SMM behaviour. This requires the control of the axiality of both ground and excited doublets, which may be achieved through the modulation of the DAD's substituents. On the other hand, 2 shows a field-induced SIM behaviour due to the presence of a strong QTM which arises from the relatively large tunnelling splitting in the non-Kramers Tb3+ ion. In contrast, the prolate density of Er3+ cannot be stabilized by the DAD ligands and the resulting compound does not show a slow relaxation.

Raman Spectroscopy and Imaging of Low-Energy Phonons

  • D. Tuschel, "Raman Spectroscopy and Imaging of Low-Energy Phonons." Spectroscopy 30(3), 14–29 (2015).

Raman bands in the low-energy region of the spectrum of crystals are attributed to so-called external lattice vibrational modes. The Raman bands from these external vibrational modes (low-energy phonons) are very sensitive to crystal structure and orientation with respect to the incident laser polarization and to molecular interactions within the crystal. The low-energy vibrational modes of many organic molecular crystals have very high Raman scattering cross-sections. Very often we deal with solid-state materials for which there may be no molecular species Raman spectroscopy of solid-state materials involves the inelastic scattering of light by phonons, quanta that have the energy of lattice vibrations. The Stokes and anti-Stokes Raman scattering consist of the generation or annihilation of a phonon in the solid，respectively. In crystalline materials, the phonons can be understood as lattice vibrational modes whether the crystal is a covalent or ionic solid or a molecular crystal. The external vibrations are generally of low energy and of course would be absent from the liquid or gas spectrum of the material because of the absence of long-range translational symmetry present in a crystal. Their Raman shifts are often similar but not identical to those of the molecular (liquid or gas) spectrum. The higher the energy of the first excited vibrational state or phonon, the lower the population of that state and the weaker the anti-Stokes Raman scattering will be.In fact, the ratio of the anti-Stokes to Stokes Raman scattering is entirely dependent on the energy of the vibrational transition and the temperature. The low-energy phonons follow the same Raman polarization selection rules that govern the higher energy phonons or internal vibrational modes. The external vibrational modes are particularly sensitive to molecular interactions and interlayer van der Waals forces.

Synthesis of gold/rare-earth-vanadate core/shell nanorods for integrating plasmon resonance and fluorescence

The nanoscale core/shell heterostructure is a particularly efficient motif to combine the promising properties of plasmonic materials and rare-earth compounds; however, there remain significant challenges in the synthetic control due to the large interfacial energy between these two intrinsically unmatched materials. Owing to the attractive integration of the plasmonic and fluorescence properties, such core/shell heterostructures will find particular applications in a wide array of areas, from biomedicine to energy.In the synthetic methodology area, with an understanding of the multiple roles of oleate, the proposed surfactant exchange method can be applied to help the rational synthesis of various metal/oxide core/shell nanostructures. Furthermore, owing to the wide applicability of the anion exchange, our synthesis strategy might be extended to the growth of other rare-earth compound shells, such as fluorides and phosphates.

Lanthanides in molecular magnetism: old tools in a new field

  • Sorace, Lorenzo , C. Benelli , and D. Gatteschi . "Lanthanides in molecular magnetism: old tools in a new field." CHEMICAL SOCIETY REVIEWS 40.6(2011):3092-0.

The starting point for the description of the low lying levels of the RE is the free ion. RE free ions can be described in the Russell–Saunders scheme as 2S+1LJ, where S is the spin quantum number, L the orbital one and |L S| r J r L + S. The complete list of states to be considered for a given ion is very large, but considering only the ground J multiplet seems to be a reasonable approximation when one is interested only in the magnetic properties. The effect of the ligand coordination is that of breaking the spherical symmetry, splitting the 2J + 1 degeneracy of the free ion state. The resulting states and their energies are computed by applying an operator equivalent approach. This means that the effect of the ligands is modelled by a potential represented by a sum of equivalent angular momentum operators, whose matrix elements are easily computed. There are several possibilities to express this potential, the most commonly used one in molecular magnetism being that reported by Stevens

Localized Surface Plasmon Resonances: Noble Metal Nanoparticle Interaction with Rare-Earth Ions

*

Additionally, metallic NPs with sizes smaller than the wavelength of light show strong dipolar excitations in the form of localized surface plasmon resonances (LSPR). LSPRs are nonpropagating excitations of the conduction electrons of metallic NPs coupled to the electromagnetic field . This effect has been the subject of extensive research, both fundamental and with a view to applications. The resonance frequency of the oscillation, i.e., the surface plasmon (SP) energy, it is essentially determined by the dielectric properties of the metal and the surrounding medium, and by the particle size and shape. The collective charge oscillation causes a large resonant enhancement of the local field inside aand near the NP. This field enhancement is used in surface-enhanced Raman scattering (SERS) and is currently discussed for potential applications in nonlinear optical devices, in optical tweezers, and generally for the manipulation of the local photonic density of states.

Finally we present diverse experimental results of the interaction of RE ions interaction with NPs, resulting in an enhancement of the intensity emission of the RE ions due to long-range electromagnetic interaction between LSPR and the RE ions. All quantities of a solid depend on an overlap of the 4f wavefunctions with those of a neighboring ion have to be small in RE compounds.

The 4f shell of the RE ions are an unfilled shell and therefore have a spherical charge distribution. If the ion is introduced into a crystal, the ion experiences an inhomogeneous electrostatic field, the so-called crystal field, which is produced by the charge distribution into the crystal. This crystal field distorts the closed shells of the RE ion. Producing an effect on the energy level 4f, i.e., removes to a certain degree the degeneracy of the free ion 4f levels, thus producing a major modification of the energy levels (but this depends on the crystal symmetry). rare-earth radiative transitions in solid hosts resemble those of the free ions and electron–phonon coupling is weak.

Nevertheless, the interactions between host and RE ions, it is necessary to consider background losses from impurity absorption and scattering mechanisms that decrease the efficiency of the optical device. For example, depending on the phonon energies of the host matrix, some of the level lifetimes can be strongly quenched by multi-phonon transitions. Such effects are minimized in low-phonon-energy host media such as fluoride fibers.

Enhanced emission from BaMgAl10O17:Eu2+ by localized surface plasmon resonance of silver particles

  • Lee, Seong Min , and K. C. Choi . "Enhanced emission from BaMgAl10O17:Eu2+ by localized surface plasmon resonance of silver particles." Optics Express 18.12(2010):12144-12152.

Localized surface plasmon is defined as the electromagnetic oscillation of surface electrons in nanoscaled metal structures. Localized surface plasmon is decided by the material, size, and shape of metal nano-structure. Contrary to propagating surface plasmon (SP), the LSP of metal nanostructure has the advantage of easily controlling the plasmon resonance wavelength and obtaining the localized field enhancement without matching the KSP vector (propagation constant).It is generally well-known that transitions 5D0→ 7F1 and 5D0→ 7F2 of the rare earth ion Eu3+ are of magnetic and electric dipole transitions

Luminescent multifunctional lanthanides-based metal–organic framework

  • Rocha, Jo?O , et al. "Luminescent multifunctional lanthanides-based metal–organic frameworks." Chemical Society Reviews 40.2(2011):926-0.

The use of LnMOFs as UC materials is rarely reported due to the existence of effective multiphonon relaxation which decreases the efficiency of the UC process

Phonon-Assisted Photoluminescence UpConversion of Silicon-Vacancy Centers in Diamond

  • Gao, Yuanfei, et al. "Phonon-Assisted Photoluminescence Up-Conversion of Silicon-Vacancy Centers in Diamond." The Journal of Physical Chemistry Letters.

Phonon assisted anti-Stokes photoluminescence (ASPL) up-conversion lies at heart of optical refrigeration in solids. The thermal energy contained in the lattice vibrations is taken away by the emitted anti-Stokes photons ASPL process, resulting in the laser cooling of solids. Up to date, net laser cooling of solids is limited in rare-earth (RE) doped crystals, glasses and direct band gap semiconductors.

Probing the Magnetic Ordering of Antiferromagnetic MnPS3 by Raman Spectroscopy

  • "Probing the Magnetic Ordering of Antiferromagnetic MnPS3 by Raman Spectroscopy." The Journal of Physical Chemistry Letters 10.11(2019):3087-3093.

In contrast, Raman spectroscopy as a fast and nondestructive characterization technique, has been extensively used to study the lattice structural, interlayer coupling, and phase transition temperature of 2D materials. In principle, the onset of magnetic ordering lowers the crystal symmetry, resulting in variation of the Raman intensity and frequency, as well as possible activation of new Raman modes.

Raman spectroscopic characterization of light rare earth ions: La3+, Ce3+, Pr3+, Nd3+ and Sm3+ – hydration and ion pair formationg

  • Rudolph, Wolfram W. , and G. Irmer . "Raman spectroscopic characterization of light rare earth ions: La\r, 3+\r, Ce\r, 3+\r, Pr\r, 3+\r, Nd\r, 3+\r, and Sm\r, 3+\r, – hydration and ion pair formation." Dalton Trans. 46.13(2017):4235-4244.

Raman spectra of aqueous La3+, Ce3+, Pr3+, Nd3+ and Sm3+ – perchlorate solutions were measured and weak strongly polarized Raman bands were detected at 343 cm−1, 344 cm−1, 347 cm−1, 352 cm−1 and 363 cm−1, respectively. The full width at half height for these bands is quite broad (∼50 cm−1) in the isotropic spectrum and the band width increases with increasing solute concentration. The polarized Raman bands were assigned to the breathing modes of the nona-aqua ions of the mentioned rare earth ions. Published structural results confirmed that these ions exist as nona-hydrates in aqueous solutions [Ln (H2O)9]3+. The Ln–O bond distances of these rare earth ions correlate well with the band positions of the nona-aqua ions [Ln(OH2)9]+3 (Ln = La3+, Ce3+, Pr3+, Nd3+ and Sm3+) and the force constants were calculated for these breathing modes. The strength of the force constants increase with decreasing the Ln–O bond distances (La–O > Ce–O > Pr–O > Nd–O > Sm–O). While the fully hydrated ions are stable in dilute perchlorate solutions (∼0.2 mol L−1), in concentrated perchlorate solutions outer-sphere ion pairs and contact ion pairs are formed (C > 1.5 mol L−1). In a hydrate melt at 161 °C of Ce(ClO4)3 plus 6H2O, the contact ion pairs are the dominate species. The Raman bands of the ligated perchlorate and the Ce–O breathing mode of the partially hydrated ion pair at 326 cm−1 were measured and characterized. In cerium chloride solutions chloro-complex formation was detected over the measured concentration range from 0.270–2.167 mol L−1. The chloro-complexes in CeCl3(aq) are weak and diminish rapidly with dilution and disappear at a concentration <0.1 mol L−1. In a CeCl3 solution, with additional HCl, a series of chloro-complex species of the type [Ce(OH2)9−nCln]+3−n (n = 1, 2) were detected.

Shell-Isolated Tip-Enhanced Raman and Fluorescence Spectroscopy

  • Huang, Ya Ping , et al. "Shell-solated Tip-nhanced Raman and Fluorescence Spectroscopy." Angewandte Chemie 130.25(2018).

Tip-enhanced Raman spectroscopy can provide molecular fingerprint information with ultrahigh spatial resolution, but the tip will be easily contaminated, thus leading to artifacts. It also remains a great challenge to establish tip-enhanced fluorescence due to quenching resulting from the proximity of the metal tip.Tip-enhanced Raman spectroscopy (TERS) combines the advantages of scanning probe microscopy and Raman spectroscopy. It provides both morphologic and chemical fingerprint information about the surface with a high detection sensitivity down to a single-molecule level and a high spatial resolution down to sub-nanometers due to the lightning-rod effect and localized surface plasmon resonance (LSPR) at the tip apex. Developed a general ALD method to prepare shell-isolated Au or Ag tips for tip-enhanced Raman or fluorescence spectroscopy. The shell-isolated Au or Ag tips with various types of shells including silica, aluminum oxide, and titanium oxide are successfully prepared via this method, and the shell thickness was precisely controlled in the range of 1–20 nm. Such tips exhibit strong electromagnetic enhancement and show great advantages for TERS in solution. Only the Raman signal of the analyte is enhanced while the interference from other molecules in the solution is completely excluded. Furthermore, tip-enhanced fluorescence has also been achieved by using the shell-isolated tips. The shell-isolated tips weaken the nonradiative energy transfer in scanning tunneling microscope (STM)-based tip-enhanced fluorescence, leading to a much higher fluorescence enhancement factor (1.7×103) compared to a bare tip. More importantly, Raman and fluorescence signals for a molecule can be obtained simultaneously, and the ratio between them can be easily tuned by varying the shell thickness. The tip coated with 2 nm silica still has strong electromagnetic enhancement performance. Further increasing the shell thickness would significantly decrease the enhancement. The ultrathin silica shell can effectively exclude interferences from impurities by suppressing their interaction with the tip and thus help to acquire clean information of the analyte of interest. Hence, such shell-isolated tips can be applied to the TERS studies in solutions containing complex components, for example, live cells, without the limitation of impurities adsorbing on the tip. In plasmon-enhanced fluorescence spectroscopy, the enhanced local EM field, which is generated by the plasmonic metallic nanostructure, can accelerate the excitation rate and spontaneous emission rate of fluorophores nearby. However, the fluorophores are usually located in the nano-gap between the metal tip and metal substrate in STM-based tip-enhanced fluorescence spectroscopy, thus nonradiative energy transfer to the metal tip and metal substrate efficiently quenches the fluorescence signals.

Shell-Isolated Nanoparticle-Enhanced Raman and Fluorescence Spectroscopies: Synthesis and Applications

  • Xu, Juan , et al. "Shell‐Isolated Nanoparticle‐Enhanced Raman and Fluorescence Spectroscopies: Synthesis and Applications." Advanced Optical Materials (2018).

Raman spectroscopy is based on the inelastic scattering of light, and it can provide abundant information about the structure and chemical bonds of molecules in a noninvasive manner.LSPR is an optical phenomenon related to the collective oscillation of free electrons in a small confined volume around a metal nanostructure.the Raman signal of TERS is considerably lower than SERS, because only one signal amplifier or plasmonic tip is applied in the system. Furthermore, it is complex and difficult to apply the TERS technique into aqueous systems, as the pollution species in the solution can be easily adsorbed on the tip surface and the Raman signal will suffer from the contamination. When the optical species are located near or on the surface of metal, a fluorescence quenching phenomenon can occur. However, the inert shell of SHINs can prevent the fluorescence quenching of optical species. Also, the intense electromagnetic field around plasmonic nanoparticles can lead to fluorescence enhancement. As a result, a thickness dependent enhancement is observed because when the shell thickness increases gradually from zero to the optimal thickness, the adsorbed fluorophores on the surface of SHINs continuously change from fluorescence quenching state to fluorescence enhancement state.The shell cannot be too thick, otherwise the electromagnetic field would be unable to reach the surface. The size, shape, and material of the plasmonic core of SHINs are all parameters that will affect the enhancement effect.According to the experimental and theoretical studies performed by Aroca, the far field fluorescence enhancement is proportional to squared local field enhancement. Additionally, the plasmon extinction should match the fluorescence emission to obtain a high enhancement factor. Due to the LSPR effect of the plasmonic metal nanoparticles, SERS can enhance the Raman signal of molecules near the electromagnetic field by several orders of magnitude. However, direct contact between the reaction molecules and the SERS substrate may cause signal deviation, change the reaction pathway, and reduce the stability of the probe.As known, the excited molecule can be seen as a dipole, and the enhanced localized electromagnetic field also has its direction. Thus the orientation of molecules in this field can have a crucial effect on the interaction between plasmonic nanostructures and molecules.

Nanoparticles with Raman Spectroscopic Fingerprints for DNA and RNA Detection

  • Cao, Yun Wei Charles , R. Jin , and C. A. Mirkin . "Nanoparticles with Raman Spectroscopic Fingerprints for DNA and RNA Detection." Science 297.

Where the sequences are very dissimilar, we found that other than the expected spectroscopic probe signature for each target, there were virtually no other detectable Raman lines, indicating no crosshybridization between different targets and probes. The SERS signal was obtained only from areas of the substrate where the Raman dye-labeled Au particles have initiated Ag formation. Therefore, this “multiple color” scanning Raman detection method does not record background signal due to Ag deposition where Au particles do not exist. This is not the case for the previous gray-scale scanometric approach, especially at ultralow target concentrations.Nanoparticle probes heavily functionalized with oligonucleotides exhibit extraordinarily sharp thermally induced denaturation transitions that lead to substantially higher selectivity than conventional molecular fluorophore probes and microscopic bead probe.

Plasmon-Induced Magnetic Resonance Enhanced Raman Spectroscopy

  • Chen, Shu , et al. "Plasmon-Induced Magnetic Resonance Enhanced Raman Spectroscopy." Nano Letters 18.4(2018).

Revealed (1) a correspondence of the strongest near-field response to the far-field scattering valley and (2) a significant improvement in Raman signals of probing molecules by the plasmon-induced magnetic resonance. It should be noted that the physical nature of the plasmon-induced magnetic mode is the same as the plasmon-induced electric mode. Both of the two modes belong to bounded surface charge density wave originating from the collective oscillation of free electrons induced by the incident light. The electric dipolar resonance is regarded as the super-radiative mode owing to the largeness of total electric dipole moment that is proportional to the nanosphere volume. Raman experimental results have further disclosed that PIMR significantly enhances the SERS response of probing molecules due to large electric-field enhancements generated by the PIMR. High capabilities of PIMR on electric and magnetic near-field enhancements originate from (a) low electromagnetic radiative losses and (b) efficient coupling between PIMR and both electric- and magnetic-field components of the incident light.

Tm3+-Sensitized NIR-II Fluorescent Nanocrystals for In Vivo Information Storage and Decoding

  • Zhang, F., Zhang, H., Fan, Y., Pei, P., Sun, C., & Lu, L. (2019). Tm3+ Sensitized 1208 nm Excitation and 1525 nm Emission NIR-II Fluorescent Nanocrystals for In vivo Information Storage and Decoding. Angewandte Chemie International Edition.

Fluorescence bioimaging techniques has been widely developed and provide real-time,non-invasive,and direct information of biospecimens.However,owing to the large absorption and scattering of photons traversing biological tissues in the visible (400–700 nm) and traditional nearinfrared (NIR-I, 700–1000 nm) regions,invivo fluorescence imaging often suffers from low penetration depth and resolution.In vivo fluorescence imaging in the second nearinfrared window (NIR-II) affords deep-tissue penetration and high spatial resolution.Rare-earth-doped nanocrystals with superior photostability and lower biotoxicity are also capable of generating intense NIR-II emissions with large Stokes shifts.Lanthanide luminescence processes typically need strong ground state absorption (GSA) transitions of the sensitizer.

Magnetically and Near-Infrared Light-Powered Supramolecular Nanotransporters for the Remote Control of Enzymatic Reactions

  • Chechetka, Svetlana A. , et al. "Magnetically and Near-Infrared Light-Powered Supramolecular Nanotransporters for the Remote Control of Enzymatic Reactions." Angewandte Chemie International Edition 55.22(2016):6476-6481.

Blood vessels are involved in many biological processes, such as the transport of biomolecules,the maintenance of homeostasis,and the development of cancer metastases.Furthermore,nano material in jections did not affect the viability and body weight of mice up to 30 days. These results indicate that our highly biocompatible nanotransporters function efficiently in the living organisms as magnetic field- and laserinduced supramolecular nanorobots.

Inorganic lanthanide nanoprobes for background-free luminescent bioassays

  • Huang, Ping , et al. "Inorganic lanthanide nanoprobes for background-free luminescent bioassays." SCIENCE CHINA Materials 58.2(2015):156-177.

Luminescent bioassay techniques have been widely adopted in a variety of research and medical institutions. However, conventional luminescent bioassays utilizing traditional bioprobes like organic dyes and quantum dots often suffer from the interference of background noise from scattered lights and autofluorescence from biological matrices. To eliminate this disadvantage, the use of inorganic lanthanide (Ln3+)-doped nanoparticles (NPs) is an excellent option in view of their superior optical properties, such as the long-lived downshifting luminescence, near-infrared triggered anti-Stokes upconverting luminescence and excitation-free persistent luminescence. Particularly, the l ong-lived downshifting luminescence (DSL) and high photochemical stability of Ln3+-doped NPs make them ideal alternative to Ln3+-chelates for TRPL biodetection to eliminate the short-lived background noise from scattered lights and autofluorescence from the biological samples . Such unwanted background noise can also be overcome by using the unique anti-Stokes upconverting luminescence (UCL) and persistent luminescence of Ln3+-doped NPs. The large anti-Stokes shift of UCL under near-infrared (NIR) excitation produces a neat emission spectrum without any interference of the excitation lights and biological autofluorescence . The long-lasting phosphorescence (LLP) nature of persistent luminescent NPs (PLNPs) allows optical excitation before signal collection, thus providing an effective strategy to thoroughly suppress the background noise originating from in situ excitation . These features promise Ln3+-doped NPs as sensitive nanoprobes for background-free luminescent bioassays. Furthermore, to avoid non-specific binding in subsequent bioanalytical applications, it is necessary to block the residual binding sites of the NPs after the conjugation. Bovine serum albumin (BSA) and human serum albumin (HSA) are frequently used for this purpose.Although the visible DSL of Ln3+-doped NPs is favorable for in vitro biodetection, it is not appropriate for in vivo bioapplications as the UV excitation light could damage biological specimens. Recently, with the rapid advances in deep-tissue bioimaging, there has reviving interest for NIR-to-NIR Ln3+-doped DSL NPs, because of their high PL efficiency and the minimal response of the cells and tissues to NIR light. The available NIR emitters include Nd3+, Yb3+, Ho3+, Er3+ and Tm3+, which are also key dopants in UCNPs for producing efficient anti-Stokes UCL, as will be overviewed in the following subsection.Owing to the remarkable light penetration depth and the absence of autofluorescence in biological specimens under NIR excitation, Ln3+-doped UCNPs are ideal for use as alternatives to conventional DSL bioprobes for various biomedical applications.By utilizing the long-lived DSL, NIR-triggered anti-Stokes UCL and excitation-free LLP of Ln3+-doped NPs, the background noise from scattered lights and autofluorescence from biological samples can be completely ruled out, thus providing a background-free signal for biodetection and a remarkable sensitivity than conventional fluorescent immunoassays. These NPs can be used either as direct biolabels in heterogeneous assays or as energy transfer donors in homogeneous FRET assays.For comparison, in non-binding control experiment, where BSA instead of β-hCG antigen was used under otherwise identical conditions, the UCL signal was hardly detectable, thus confirming the high specificity of the assay. The LOD was determined to be ~3.8 ng mL−1, comparable to the normal range of human serum hCG level. It is fundamentally important to develop general and economic protocols for the synthesis, surface modification and bioconjugation of high-quality Ln3+-doped luminescent nanoprobes that are optimized for bioassay applications without any concerns of biocompatibility, stability and long-term toxicity.

Highly-reproducible Raman scattering of NaYF4:Yb,Er@SiO2@Ag for methylamphetamine detection under near-infrared laser excitation

  • Ma, Yongmei , et al. "Highly-reproducible Raman scattering of NaYF4:Yb,Er@SiO2@Ag for methylamphetamine detection under near-infrared laser excitation." Analyst 140(2015).

The laser power of UV/visible light may damage the target molecules for the long illumination time especially in the presence of O2. Upconversion (UC) emission materials can convert infrared radiation into visible light refers to non-linear optical processes that convert two or more low-energy pump photons to a higher energy output photon. In addition, UC materials show a sharp emission bandwidth, large anti-Stokes shifts, high photostability, tunable emission, and low cytotoxicity, which leads to potential applications in lasers, next-generation lighting, infrared quantum counters, biological macromolecular systems and has been used in a variety of assay formats ranging from bio-detection to cancer therapy.The SiO2 shell can prevent phase change of NaYF4:Yb,Er because of the deposition of Ag NPs. Furthermore,the surface of SiO2 exhibit highly biocompatible, easy surface modification, and easy control of interparticle interactions. In the 40presence of noble metals NPs, such as Au and Ag NPs, the broad absorption of noble metals can increase the power of the excitation by local field enhancement ,resulted in the increase of excited Yb3+ ions, and more energy was transferred from excited Yb3+ to Er3+. The presence of UC materials contributed the major part of SERS enhancement of UC@SiO2@Ag nanoparticles under NIR excitation. Consequently, the Raman signals of molecules also become stronger with higher Raman cross-section and dipole moment induced by the high local field density

Physics

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Biochemistry