Fernando Rodríguez

Universidad de Cantabria | UNICAN · Faculty of Sciences

Metal-to-metal multiple bonds between d elements have been traditionally described using the σ < π < δ < δ* < π* < σ* energy ordering for their molecular orbitals. Nonetheless, for species with more than 8 bonding electrons, the situation may be more complex. This is the case of paddlewheel-type compounds with Ru 2 5+ cores, in which generally the...

We report an extensive study of the optical and structural properties of NiWO4 combining experiments and density functional theory calculations. We have obtained accurate information on the pressure effect on the crystal structure determining the equation of state and compressibility tensor. We have also determined the pressure dependence of the ba...

The mechanical properties and stability of metal nanoparticle colloids under high-pressure conditions are investigated by means of optical extinction spectroscopy and small-angle X-ray scattering (SAXS), for colloidal dispersions of gold nanorods and gold nanospheres. SAXS allows us to follow in situ the structural evolution of the nanoparticles in...

High-pressure optical-absorption measurements performed on polycrystalline Co(IO3)2 samples were used to characterize the influence of pressure on the electronic d–d transitions associated with Co2+ and the fundamental band gap of Co(IO3)2. The results shed light on the electron-lattice coupling and show that Co(IO3)2 exhibits an unusual behavior b...

DOI:https://doi.org/10.1103/PhysRevLett.128.099701

The understanding of the interplay between crystal structure and electronic structure in semiconductor materials is of great importance due to their potential technological applications. Pressure is an ideal external control parameter to tune the crystal structures of semiconductor materials in order to investigate their emergent piezo-electrical a...

An advanced experimental and theoretical model to explain the correlation between the electronic and local structure of Eu $$^{2+}$$ 2 + in two different environments within a same compound, EuS, is presented. Eu X monochalcogenides ( X : O, S, Se, Te) exhibit anomalies in all their properties around 14 GPa with a semiconductor to metal transition....

We present a spectroscopic study of the doubly Mn ⁴⁺ and Cr ³⁺ -doped Sr 4 Al 14 O 25 , synthesised via solid state reaction, as a function of pressure and temperature to check its potential as a...

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 pr...

An advanced experimental and theoretical model to explain the correlation between the electronic and local structure of Eu2+ in two different environments within a same compound, EuS, is presented. EuX monochalcogenides (X: O, S, Se, Te) exhibit anomalies in all their properties around 14 GPa with a semiconductor to metal transition. Although it is...

The density and compressibility of nanoscale gold (both nanospheres and nanorods) and microscale gold (bulk) were simultaneously studied by X-ray diffraction with synchrotron radiation up to 30 GPa. Colloidal stability (aggregation state and nanoparticle shape and size) in both hydrostatic and nonhydrostatic regions was monitored by small-angle X-r...

This work investigates the Ni-F distance dependence of the crystal-field (CF) transitions of Ni2+ in KNiF3 by high-pressure spectroscopy. All peaks shift to higher energy with pressure according to trends foreseen by the Tanabe-Sugano diagram. At ambient conditions, we obtain Racah and CF splitting parameters of B=0.118eV, 10Dq=0.908eV; C/B=4.4 (10...

Graphene oxide, integrated with the filamentous bacteriophage M13, forms a 3D large-scale multifunctional porous structure by self-assembly, with considerable potential for applications. We performed Raman spectroscopy under pressure on this porous composite to understand its fundamental mechanics. The results show that at low applied pressure, the...

CsPbCl3 is considered as a structural archetype for hybrid organic-inorganic lead perovskite halides: APbX3 with A: organic cation, i.e. alkylammonium; X: Cl, Br, I [1-5]. Their enhanced optoelectronic and photovoltaic properties and the difficulty to establish structural correlations in these compouns make it the study of simple perovskites necess...

GO is a water-soluble nanomaterial prepared through extensive chemical attack of graphite crystals to introduce oxygen-containing defects in the graphite stack. In GO, a large fraction (0.5-0.6) of carbon is sp 3 hybridized and co-valently bonded with oxygen in form of epoxy and hy-droxyl groups. The remaining carbon is sp 2 hybridized and bonded e...

Pr3+-doped Y2O3 nanocrystals (NCs) have been obtained via five wet-chemistry synthesis methods which were optimized in order to achieve superior optical properties. To this end, a systematic study on the influence of different reaction parameters was performed for each procedure. Specifically, precursor concentration, reaction temperature, calcinat...

The optical properties of a sparsely investigated material, LaGdO3 doped with Er3+,are explored regarding its suitability as nanothermometer. Besides its excellent capabilities for dielectric applications, when doping with Er3+, this material provides a highly efficient upconversion photoluminescence (PL) for high temperature thermometry at high pr...

The sensing capabilities of gold nanorods under high-pressure conditions were investigated in methanol-ethanol mixtures (up to 13 GPa) and in water (up to 9 GPa) through their optical extinction. The longitudinal SPR band of AuNR exhibits a redshift with pressure which is the result of two main competing effects: compression of the conduction elect...

The effects of pressure in electronic and vibrational properties of the double perovskite CaCu 3 Ti 4 O 12 have been investigated in the 0-25 GPa range by optical absorption and Raman spectroscopy. Besides a full structural characterization, we aim at unveiling whether the ambient I m 3 ¯ crystal structure is stable under high pressure conditions a...

In-situ single-crystal diffraction and spectroscopic techniques have been used to study a previously unreported Cu-framework bis[1-(4-pyridyl)butane-1,3-dione]copper(II) (CuPyr-I). CuPyr-I was found to exhibit high-pressure and low-temperature phase transitions, piezochromism, negative linear...

In the last years the two-dimensional perovskites have focused considerable attention for their potential applications for optoelectronics. Contrary to previous publications we demonstrate that (CH3NH3)2CuX4 hybrid organic-inorganic layered perovskite does not show any room-temperature photoluminescence (PL) under UV excitation. This statement can...

The localized surface plasmon resonance (LSPR) of gold nanospheres dispersed in methanol-ethanol 4:1 was measured as a function of pressure up to 60 GPa. The LSPR exhibits an intense redshift with pressure in the range of 0-10 GPa, followed by a slower blueshift at higher pressures. This is because an increase in the solvent refractive index with p...

We investigated the optical properties (absorption, luminescence and Raman spectra) of nanopolycrystalline diamond (NPD) aiming at exploring its capabilities as a pressure sensor and as a pressure-cell anvil for combined X-ray/neutron and optical studies. Notably, we analysed the Raman peak shift and broadening with pressure using a Moissanite Anvi...

The search of material hosts being able to incorporate Er³⁺ impurities with a thermally stable structure and high melting temperature is priority in optical thermometry. In this work, we report on the structural and spectroscopic characterization of Er³⁺–doped and Yb³⁺/Er³⁺–co-doped LaGdO₃ nano...

This work addresses a fundamental question: To what extent is graphene graphite? In particular does 2D graphene have many of the same 3D mechanical properties as graphite, such as the bulk modulus and elastic constant c33? We have obtained, for the first time, unambiguous Raman spectra from unsupported monolayer graphene under pressure. We have use...

We have investigated the crystal structure of $Cs_2CuCl_4$ in the 0-20 GPa range as a function of pressure and how pressure affects its electronic properties by means of optical absorption spectroscopy. In particular, we focused on the electronic properties in the low-pressure Pnma phase, which are mainly related to the tetrahedral $CuCl_4^{2-}$ un...

By using optical absorption and Raman spectroscopy, we have investigated the effects of pressure in the structural, electronic, and vibrational properties of Cs2CuCl4 in the 0–20 GPa range. Our study has provided a complete characterization of the electronic and vibrational structures of Cs2CuCl4 in the low-pressure Pnma phase as a function of cell...

The interplay between spin states and metallization in compressed CoCl2 is investigated by combining diffraction, resistivity and spectroscopy techniques under high-pressure conditions and ab-initio calculations. A pressure-induced metallization along with a Co2+ high-spin (S = 3/2) to low-spin (S = 1/2) crossover transition is observed at high pre...

The effects of hydrostatic pressure on the surface plasmon resonances (SPR) of aqueous dispersions of monodisperse gold nanorods were determined up to 9 GPa. The ultranarrow longitudinal SPR band of monodisperse nanorods allows us to monitor a gradual redshift with pressure, which shows abrupt jumps at the liquid to ice phase VI and ice phase VII t...

Previous Raman measurements on supported graphene under high pressure reported a very different shift rate of in-plane phonon frequency of graphene (16 cm$^{-1}$GPa$^{-1}$) from graphite (4.7 cm$^{-1}$GPa$^{-1}$), implying very different in-plane anharmonicity that graphene gets stiffer than graphite in-plane under the same pressure. It was suggest...

The surface plasmon resonances of gold nanospheres and nanorods have been measured as a function of hydrostatic pressure up to 17 GPa in methanol-ethanol 4:1 solvent and up to 10 GPa in paraffin. Both the sphere resonance and the longitudinal rod resonance exhibit redshifts, whereas the transverse rod mode shows an extremely weak redshift or bluesh...

Here we report a structural characterization study of glass-ceramics as a function of pressure by Raman spectroscopy. We selected a glass-ceramics of Li₂O-Al₂O₃-nSiO₂ (n ≈ 8) doped with ZrO₂ and TiO₂. This composition induces slight structural modification in Si-O and Si-O-Si bonds i...

This work reports an alternative method for determining thermal degradation of graphite-based thin film hydrophobic coatings using the D and G graphite vibrations as a probe. We show that the Raman spectrum of the coating as a function of temperature is an efficient probe for detecting changes in the surface properties. Both D and G bands of graphi...

The phase transition sequences of two members of the tetramethylammonium tetrachlorometallate(III) family of hybrid organic–inorganic salts have been determined and structurally characterized as a function of temperature for the first time. Unusually, a reduction in point-group symmetry with increasing temperature until reaching a cubic prototype p...

This work reports an optical absorption study on CoF2 under high-pressure conditions in the 0-80 GPa range. A recent structural study¹ performed on the pressure-induced phase-transition sequence of CoF2 reveals that this compound undergoes a structural transformation associated with a change of Co²⁺ coordination from 6 (rutile type) to 8 (fluorite...

Jahn-Teller (JT) transition-metal ions like Cu\(^{2+}\) (\(d^9\)) or Mn\(^{3+}\) (\(d^4\)) in octahedral coordination exhibit larger distortions than non-JT ions like Mn\(^{2+}\) or Fe\(^{3+}\) (both \(d^5\)) in oxides and halides with perovskite type structure. Their mutual interactions eventually determine the type of distortion and the way they...

This work investigates why Jahn-Teller (JT) transition-metal ions like Cu(2+) (d(9)) or Mn(3+) (d(4)) with octahedral coordination exhibit low-symmetry distortions of the CuF6(4-) (or MnF6(3-)) octahedron, when Cu(2+) replaces Zn(2+) either in the cubic perovskite KZnF3 or in the layer perovskite K2ZnF4. The aim is to establish correlations between...

We report the results of the Rietveld refinement, photoluminescence and Raman spectroscopy of Mn-doped ZnO ceramic pellets. Rietveld refinement shows that samples crystallize in the wurtzite structure and for the Mn-doped sample indicates that the Mn atoms substitute the Zn tetrahedral crystallographic sites in the ZnO host lattice. The emission an...

This work investigates the high-pressure structure of Cs2CoCl4 and how it affects the electronic and vibrational properties using optical absorption, Raman spectroscopy, x-ray diffraction, and x-ray absorption in the 0–15 GPa range. In particular, we focus on the electronic and local structures of Co2+, since compression of Cs2CoCl4 yields structur...

The phase transition sequences of two members of the tetramethylammonium tetrachlorometallate(III) family of hybrid organic inorganic salts have been determined and structurally characterized as a function of temperature for the first time. Unusually, we observe a reduction in point-group symmetry with increasing temperature until reaching a cubic...

This work investigates the photoluminescence properties of high transmission glass (HTG) doped with CeO2 and MnO as well as their capability to transform the solar spectrum by absorption/emission via energy transfer from Ce3+ to Mn2+ into a more efficient red-enhanced spectrum for traditional Si-based solar cells. We show that Mn3+ and Mn2+ centers...

This work investigates the energy transfer from Ce³⁺ to Mn²⁺ in high transmission glass (HTG) doped with CeO2 and MnO through time-resolved spectroscopy to transform the solar spectrum into a more efficient red-enhanced spectrum for traditional Si-based solar cells. We show that both Mn³⁺ and Mn²⁺ and Ce³⁺ and Ce⁴⁺ centres are formed in HTG through...

Two-dimensional atomic crystals, such as graphene, hexagonal boron nitride, and transition metal dichalcogenides (TMDCs), have attracted considerable attention because of their unique electrical, optical, and mechanical properties.The last class of materials is especially interesting for the next generation of electronic and optoelectronic devices...

Crystal Field Theory (CFT) predicts that crystal field acting on an Transition-Metal ( TM ) ion complex of cubic symmetry varies as R ^-5, where R is the TM -ligand distance. Yet simple and old-fashioned, CFT is used extensively since it provides excellent results in most TM ion-bearing systems, although no direct and thorough validation...

This paper investigates the electronic structure of wurtzite (W) and rock-salt (RS) Zn1-xCoxO nanoparticles (NPs) by means of optical measurements under pressure (up to 25 GPa), X-ray absorption and Transmission Electron Microscopy. W-NPs were chemically synthesized at ambient conditions and RS-NPs were obtained by pressure-induced transformation o...

The study of the G-mode pressure coefficients of carbon nanotubes, reflecting the stiff sp2 bond pressure dependence, is essential to the understanding of their extraordinary mechanical properties as well as fundamental mechanics. However, it is hindered by the availability of carbon nanotubes samples only as bundles or isolated with surfactants. O...

Over the last two decades it has been demonstrated that size effects have significant consequences for the atomic arrangements and phase behaviour of matter under extreme pressure. Furthermore, it has been shown that understanding of how size affects critical pressure-temperature conditions provides vital guidance in the search for materials with n...

CdSe is a well-studied II-VI direct gap semiconductor due to its many applications. The bulk crystallizes in the hexagonal wurtzite (W) structure with a direct energy gap ( ) of Eg= 1.7 eV at 300 K1. High-pressure spectroscopy is a very useful tool to understand the electronic structure of semiconductors, as well as to detect phase transformations....

Non- Hydrostatic Pressure dependence of Raman modes in Monolayer Graphene J. González a*, R. Valiente b, F. Rodríguez a a Malta-Consolider Team, CITIMAC, Universidad de Cantabria, Santander, Spain bMalta Consolider Team, Departamento de Física Aplicada-IDIVAL, Universidad de Cantabria, Santander, Spain Raman spectroscopy studies performed in grap...

􀀰􀁌􀁆􀁕􀁒􀁖􀁆􀁒􀁓􀁌􀁒􀀃􀀋􀀃􀁆􀁒􀁑􀀃􀁹􀁓􀁗􀁌􀁆􀁄􀀃􀁇􀁈􀀃􀁇􀁒􀁅􀁏􀁈􀀃􀁒􀁅􀁍􀁈􀁗􀁌􀁙􀁒􀀃􀁓􀁄􀁕􀁄􀀃􀁏􀁄Microscopio (10) con óptica de doble objetivo para la caracterización espectroscópica de una muestra cuya área está comprendida en el rango que va desde los micrómetros cuadrados hasta las décimas de milímetros cuadrados, que comprende un sistema de iluminación (12, 30) configurado para iluminar la...

The cross-relaxation process between the lower excited states of thulium ions has a strong influence on its main infrared emissions, but also in the population of higher excited states that lead to characteristic blue upconversion. This work investigates this process in LiNbO3:Tm3+ by means of time-resolved spectroscopy at high pressure. It is demo...

The study of carbon nanotubes(CNTs) G-Mode(GM) pressure coefficients, reflecting the stiff sp2 bond pressure dependence, is essential to the understanding of their extraordinary mechanical properties as well as fundamental mechanics. However, it is hindered by the availability of CNTs samples only as bundles or isolated with surfactants. Octadecyla...

This work reports an X-ray diffraction, X-ray absorption, and Raman spectroscopy study of [(CH3)(4)N](2)MnX4 (X = Cl, Br) under pressure. We show that both compounds share a similar phase diagram with pressure. A P2(1)/c monoclinic structure describes precisely the [(CH3)(4)N](2)MnCl4 crystal in the 0.1-6 GPa range, prior to crystal decomposition a...

An optical absorption study of Subramanian's solution shows that a [FeCl

By means of Optical Absorption, EPR and Mössbauer techniques it is demonstrated that the addition of small amounts of water to solutions of FeCl

By measuring the magnetization at low temperatures (near 1 K) and intense magnetic fields ( ≳100 KG), information about oligomer formation in ferric salts solutions can be obtained. It is shown that, under rather general conditions, the magnetic moment per ferric ion of a given ferric solution measured in the saturation regime should be equal to 5...

This work investigates the Mn2+ electronic structure and exciton dynamics in one-dimensional (1D) N(CH3)4MnCl3 (TMMC) through time-resolved excitation/emission spectroscopy and absorption measurements in the 0-10 GPa pressure range for different Cu2+ doping concentrations. The local and crystal structures have been analyzed by Raman spectroscopy an...

We use 488 and 568nm laser Raman spectroscopy under high pressure to selectively follow evolution of Raman G-mode signals of single-walled carbon nanotubes (SWCNTs) of selected diameters and chiralities ((6, 5) and (6, 4)). The G-mode pressure coefficients of tubes from our previous work are consistent with the thick-wall tube model. Here we report...

This work investigates the electronic structure and photoluminescence properties of Co2+-doped ZnO and their pressure and temperature dependences through high-resolution absorption and emission spectroscopy as a function of Co2+ concentration and their structural conformations as a single crystal, thin film, nanowire, and nanoparticle. Absorption a...

We report a complete structural study of CoF2 under pressure. Its crystal structure and vibrational and electronic properties have been studied both theoretically and experimentally using first-principles density functional theory (DFT) methods, x-ray diffraction, x-ray absorption at Co K-edge experiments, Raman spectroscopy, and optical absorption...

This work investigates the electronic structure and photoluminescence (PL) of Co2+-doped MgAl2O4 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 configuratio...

Strong colors: The solvation structure of copper(II) ions in water can be determined by optical absorption spectroscopy. Focus is placed on the absorption intensity (green: Cs(2) Cu(SO(4) )(2) ⋅6 H(2) O, black: CuSO(4) ⋅5 H(2) O, red: Cu(2+) in aqueous solution, and blue: Cu(2+) in glass). A dynamical model based on a Jahn-Teller-distorted complex...

High-pressure optical-absorption measurements performed in CuWO(4) up to 20 GPa provide experimental evidence of the persistence of the Jahn-Teller (JT) distortion in the whole pressure range both in the low-pressure triclinic and in the high-pressure monoclinic phase. The electron-lattice couplings associated with the e(g)(E⊗e) and t(2g)(T⊗e) orbi...