Pressure dependence of raman modes in double wall carbon nanotubes filled with 1D tellurium

The preparation of highly anisotropic one-dimensional (1D) structures confined into carbon nanotubes (CNTs) in general is a key objective in nanoscience. In this work, capillary effect was used to fill double wall carbon nanotubes (DWCNTs) with trigonal Tellurium. The samples are characterized by high resolution transmission electronic microscopy and Raman spectroscopy. In order to investigate their structural stability and unravel the differences induced by intershell interactions, unpolarized Raman spectra of radial and tangential modes of DWCNTs filled with 1D nanocrystalline Te excited with 514 nm were studied at room temperature and high pressure. Up to 11 GPa we found a pressure coefficient of 3.7 cm−1 GPa−1 for the internal tube and 7 cm−1 GPa−1 for the external tube. In addition, the tangential band of the external and internal tubes broaden and decrease in amplitude. All findings lead to the conclusion that the outer tube acts as a protection shield for the inner tube (at least up 11 GPa). No pressure-induced structural phase transition was observed in the studied range

Pressure-induced Co2+ photoluminescence quenching in MgAl2O4

This work investigates the electronic structure and photoluminescence (PL) of Co2+-doped gAl2O4 and their pressure dependence by time-resolved spectroscopy. The variations of the visible absorption band and its associated emission at 663 nm (τ = 130 ns at ambient conditions) with pressure/temperature can be explained on the basis of a configurational energy model. It provides an interpretation for both the electronic structure and the excited-state phenomena yielding photoluminescence emission and the subsequent quenching. We show that there is an excited-state crossover (ESCO) [4T1(P)↔2E(G)] at ambient pressure, which is responsible for the evolution of the emission spectrum from a broadband emission between 300 K and 100 K to a narrow-line emission at lower temperatures. Contrary to expectations from the Tanabe-Sugano diagram, instead of enhancing ESCO phenomena, pressure reduces PL and even suppresses it (PL quenching) above 6 GPa. We explain such variations in terms of pressure-induced nonradiative relaxation to lower excited states: 2E(G)→4T1(F). The variation of PL intensity and its associated lifetime with pressure supports the proposed interpretation.Financial support from the Spanish Ministerio de Economia y Competitividad (Project No. MAT2011-28868-C02-01) and MALTA INGENIO-CONSOLIDER 2010 (Ref. CDS2007-0045) is acknowledged. L.N. thanks the University of Cantabria for a postdoctoral fellowship grant

Understanding the Efficiency of Mn4+ Phosphors: Study of the Spinel Mg2Ti1-xMnxO4

We present a spectroscopic study of Mn-doped Mg2TiO4 as a function of pressure and temperature to check its viability as a red-emitting phosphor. The synthesis following a solid-state reaction route yields not only the formation of Mn4+ but also small traces of Mn3+. Although we show that Mn4+ photoluminescence is not appreciably affected by the presence of Mn3+, its local structure at the substituted Ti4+ host site causes a reduction of the Mn4+ pumping efficiency yielding a drastic quantum-yield reduction at room temperature. By combining Raman and time-resolved emission and excitation spectroscopies, we propose a model for explaining the puzzling nonradiative and inefficient pumping processes attained in this material. In addition, we unveil a structural phase transition above 14 GPa that worsens their photoluminescence capabilities. The decrease of emission intensity and lifetime with increasing temperature following different thermally activated de-excitation pathways is mostly related to relatively small activation energies and the electric−dipole transition mechanism associated with coupling to odd-parity vibrational modes. A thorough model based on the configurational energy level diagram to the A1g normal mode fairly accounts for the observed excitation and emissionthe quantum yieldof this material

Development of an accurate method for dispersion and quantification of carbon nanotubes in biological media

Understanding the biological effects triggered by nanomaterials is crucial, not only in nanomedicine but also in toxicology. The dose-response relation is relevant in biological tests due to its use for determining appropriate dosages for drugs and toxicity limits. Carbon nanotubes can trigger numerous unusual biological effects, many of which could have unique applications in biotechnology and medicine. However, their resuspension in saline solutions and the accurate determination of their concentration after dispersion in biological media are major handicaps to identify the magnitude of the response of organisms as a function of this exposure. This difficulty has led to inconsistent results and misinterpretations of their in vivo behavior, limiting their potential use in nanomedicine. The lack of a suitable protocol that allows comparing different studies of the content of carbon nanotubes and their adequate resuspension in culture cell media gives rise to this study. Here, we describe a methodology to functionalize, resuspend and determine the carbon nanotube concentration in biocompatible media based on UV-Vis spectroscopy. This method allows us to accurately estimate the concentration of these resuspended carbon nanotubes, after removing bundles and micrometric aggregates, which can be used as a calibration standard, for dosage-dependent studies in biological systems. This method can also be extended to any other nanomaterial to properly quantify the actual concentration.This work has been funded by the Instituto de Salud Carlos III (ISCiii) (ref. PI16/00496, PI19/00349, DTS19/00033); co-funded by ERDF/ESF, “Investing in your future”; the Spanish MINECO (project ref. PGC2018-101464-B-I00) and MICINN NanoBioApp Network (MINECO-17-MAT2016-81955-REDT). Authors also thank the networks Raman4Clinics (BM1401). CRL thanks the MINECO for the Juan de la Cierva Formación grant (ref. FJCI-2015-25306) and LGL the ISCiii for the Sara Borrell grant (ref. CD17/00105). The authors want to also thank the IDIVAL for financial support (refs. NVAL18/07, INNVAL18/28) and technical support

Upconversion and Optical Nanothermometry in LaGdO3: Er3+ Nanocrystals in the RT-900 K Range

This work has been supported by the Spanish Ministerio de Economía, Industria y Competitividad (Projects Nos. MAT2015-69508-P and PGC2018-101464-B-I00), the European Research Council (Ref. NCLas H2020-EU829161), and BSH Electrodomésticos España, S.A

Magnetic properties of a family of [MnIII4LnIII4] wheel complexes: an experimental and theoretical study

The chelating ligand 1,3-bis(tris(hydroxymethyl)methylamino)propane (H6L) has been used to synthesize a family of octanuclear heterometallic complexes with the formula (NMe4)3[Mn4Ln4(H2L)3(H3L)(NO3)12] (Ln = La (1), Ce (2), Pr (3), Nd (4)). Encapsulation by the ligand causes the Mn(III) centers to lie in an unusually distorted (∼C2v) environment, which is shown by density functional theory and complete active space self-consistent field calculations to impact on the magnetic anisotropy of the Mn(III) ion. The theoretical study also supports the experimental observation of a ferromagnetic superexchange interaction between the Mn(III) ions in 1, despite the ions being separated by the diamagnetic La(III) ion. The optical properties of the compounds show that the distortion of the Mn(III) ions leads to three broad absorption bands originating from the transition metal ion, while the Nd(III) containing complex also displays some weak sharp features arising from the lanthanide f–f transitions

Engineering Sub-Cellular Targeting Strategies to Enhance Safe Cytosolic Silica Particle Dissolution in Cells

Mesoporous silica particles (MSP) are major candidates for drug delivery systems due to their versatile, safe, and controllable nature. Understanding their intracellular route and biodegradation process is a challenge, especially when considering their use in neuronal repair. Here, we characterize the spatiotemporal intracellular destination and degradation pathways of MSP upon endocytosis by HeLa cells and NSC-34 motor neurons using confocal and electron microscopy imaging together with inductively-coupled plasma optical emission spectroscopy analysis. We demonstrate how MSP are captured by receptor-mediated endocytosis and are temporarily stored in endo-lysosomes before being finally exocytosed. We also illustrate how particles are often re-endocytosed after undergoing surface erosion extracellularly. On the other hand, silica particles engineered to target the cytosol with a carbon nanotube coating, are safely dissolved intracellularly in a time scale of hours. These studies provide fundamental clues for programming the sub-cellular fate of MSP and reveal critical aspects to improve delivery strategies and to favor MSP safe elimination. We also demonstrate how the cytosol is significantly more corrosive than lysosomes for MSP and show how their biodegradation is fully biocompatible, thus, validating their use as nanocarriers for nervous system cells, including motor neurons.This research was funded by ISCIII Projects ref. PI16/00496, PI19/00349, DTS19/00033, co-funded by ERDF/ESF, "Investing in Your Future"; and MICINN Projects ref. CTM2017-84050-R, NanoBioApp Network (MINECO-17-MAT2016-81955-REDT), COST action Nano2Clinic CA17140, Xunta de Galicia (Centro Singular de Investigación de Galicia-Accreditation 2016-2019 and EM2014/035), European Union FEDER Funds (European Regional Development Fund-ERDF) and IDIVAL for INNVAL 17/11, INNVAL18/28, INNVAL19/18 and the technical support

Tris(bipyridine)Metal(II)-Templated Assemblies of 3D Alkali-Ruthenium Oxalate Coordination Frameworks: Crystal Structures, Characterization and Photocatalytic Activity in Water Reduction

A series of 3D oxalate-bridged ruthenium-based coordination polymers with the formula of {[ZII(bpy)3][MIRu(C2O4)3]}n (ZII = Zn2+ (1), Cu2+ (3, 4), Ru2+ (5, 6), Os2+ (7, 8); MI = Li+, Na+; bpy = 2,2?-bipyridine) and {[ZnII(bpy)3](H2O)[LiRu(C2O4)3]}n (2) has been synthesized at room temperature through a self-assembly reaction in aqueous media and characterized by single-crystal and powder X-ray diffraction, elemental analysis, infrared and diffuse reflectance UV?Vis spectroscopy and thermogravimetric analysis. The crystal structures of all compounds comprise chiral 3D honeycomb-like polymeric nets of the srs-type, which possess triangular anionic cages where [ZII(bpy)3]2+ cationic templates are selectively embedded. Structural analysis reveals that the electronic configuration of the cationic guests is affected by electrostatic interaction with the anionic framework. Moreover, the MLCT bands gaps values for 1?8 can be tuned in a rational way by judicious choice of [ZII(bpy)3]2+ guests. The 3D host-guest polymeric architectures can be used as self-supported heterogeneous photocatalysts for the reductive splitting of water, exhibiting photocatalytic activity for the evolution of H2 under UV light irradiationThe authors thank FEDER and Spanish MINECO for financial support under Projects MAT2013-40950-R, UCAN08-4E-008, MAT2012-38664-C02-1 and Consolider ORFE

Pressure effects on Jahn-Teller distortion in perovskites: The roles of local and bulk compressibilities

The interplay between the Jahn-Teller (JT) effect and octahedron tilting in transition-metal perovskites is investigated as a function of pressure. Our focus is on its effects on the exchange and electron-phonon interactions, both having a strong influence on materials properties. We demonstrate that the JT distortion in Cu2+ and Mn3+ is reduced upon compression and is eventually suppressed at pressures above 20 GPa. X-ray diffraction and x-ray absorption measurements in A2CuCl4 layer perovskites (A: Rb, CnH2n+1NH3; n = 1–3) show that, although pressure slightly reduces the long Cu-Cl distance in comparison to the Cu-Cu distance in the layer, the JT distortion is stable in the 0–20 GPa range. The difference between lattice (βC 0 = 0.14 GPa−1) and local CuCl6 (β0 = 0.016 GPa−1) compressibilities, together with the high stability of the JT distortion, lead to CuCl6 tilts upon compression. The evolution of the elongated CuCl6 octahedron in A2CuCl4, as well as MnF6 in CsMnF4 and MnO6 in LaMnO3 and DyMnO3, toward a nearly regular octahedron takes place above 20 GPa, in agreement with experimental results and a model analysis based on the JT energy derived from optical absorption spectroscopy: EJT = 0.25–0.45 eV/Cu2+, EJT = 0.45 eV/Mn3+ (CsMnF4), and EJT = 0.25 eV/Mn3+ (LaMnO3). The proposed model clarifies controversial results about pressure-induced JT quenching in Cu2+ and Mn3+ systems, providing an efficient complementary means to predict pressure behavior in perovskites containing JT transition-metal ions.Financial support from the Spanish Ministerio de Ciencia e Innovacion (Grant No. MAT2008-06873-C02-01/MAT) ´ is acknowledged. X-ray absorption and diffraction experiments were done at D11/LURE (Project PS203-01), and ID09A/ESRF (HS2159), respectively. The MALTA Consolider Ingenio 2010 program (CSD2007-00045) is also acknowledged

Photoluminescence and Raman study of the high-pressure behavior of monoclinic (Eu1-xYbx)2O3 solid solution

The high-pressure behavior of (Eu1-xYbx)2O3 solid solution with Yb3+ content (x) between 0 and 0.2 and monoclinic (B-type) crystalline structure has been studied by means of Raman and photoluminescence spectroscopies up to 15 GPa. A reversible phase transition from the monoclinic (B) to trigonal (A) phase has been observed for all compositions by Raman, with the transition pressure linearly increasing with x. The same conclusion was reached using the Eu3+ photoluminescence as a local probe. The fraction of B and A phases as a function of pressure has been estimated through the integrated intensity of the Eu3+5D0-7F0 electronic transition. The possibility of using the evolution of the spectral distribution of the 5D0-7F2 transition to estimate the fraction of each phase with pressure has been also discussed. Moreover, the spectral shifts of the 5D0-7F0 and 5D0-7F1 transitions with pressure have been used to evaluate the effect of pressure on the spin-orbit coupling constant ?4fThe authors acknowledge financial support from the European Union (FET Open project NCLas, ref. H2020-EU829161) and the Spanish Ministerio de Ciencia, Innovación y Universidades (PGC2018–101464-B-I00 and PID2021–127656NB-I00). M.T.C. would also like to thank the University of Cantabria for the pre-doctoral grant "Concepción Arenal", co-financed by the Government of Cantabria