Person: González Calbet, José María
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First Name
José María
Last Name
González Calbet
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Química Inorgánica
Area
Química Inorgánica
Identifiers
5 results
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Now showing 1 - 5 of 5
Item New insights into the luminescence properties of a Na stabilized Ga-Ti oxide homologous series(Journal of materials chemistry C, 2020) García Fernández, Javier; García Carrión, Marina; Torres Pardo, Almudena; Martínez Casado, Ruth; Ramírez Castellanos, Julio; Nogales Díaz, Emilio; González Calbet, José María; Méndez Martín, BianchiHerein, we achieve the synthesis and structural study of a luminescent Na-stabilized Ga-Ti oxide homologous series by atomically resolved electron microscopy. Relevant optical properties as a function of the titanium content have been revealed. In particular, the excitation and emission bands change with the series term, showing wide tunability of the luminescence bands, ranging from the ultraviolet to the infrared. First principles studies of these structures have been done in the framework of density functional theory (DFT) to understand the optical properties. Good agreement with the experimental measurements for the three synthesized terms has been obtained from the perspective of the composition and occupancy of the crystallographic sites, as well as from the energy band structure point of view. This work paves the way to explore further the capabilities of tuning the electronic and optical properties in a variety of application fields.Item Evaluation of the Nanodomain Structure in In-Zn-O Transparent Conductors(Nanomaterials, 2021) García-Fernández, Javier; Torres-Pardo, Almudena; Ramírez Castellanos, Julio; Rossell, Marta D.; González Calbet, José MaríaThe optimization of novel transparent conductive oxides (TCOs) implies a better understanding of the role that the dopant plays on the optoelectronic properties of these materials. In this work, we perform a systematic study of the homologous series ZnkIn2Ok+3 (IZO) by characterizing the specific location of indium in the structure that leads to a nanodomain framework to release structural strain. Through a systematic study of different terms of the series, we have been able to observe the influence of the k value in the nano-structural features of this homologous series. The stabilization and visualization of the structural modulation as a function of k is discussed, even in the lowest term of the series (k = 3). The strain fields and atomic displacements in the wurtzite structure as a consequence of the introduction of In3+ are evaluated.Item Influence of cation substitution on the complex structure and luminescent properties of the Zn_kIn_2O_(k+3) system(Chemistry of materials, 2020) García Fernández, Javier; Torres Pardo, Almudena; Bartolomé Vílchez, Javier; Martínez Casado, Ruth; Zhang, Qing; Ramírez Castellanos, Julio; Terasaki, Osamu; Cremades Rodríguez, Ana Isabel; González Calbet, José MaríaThe effect of In^(3+) substitution by Ga^(3+) or Al^(3+) on the structure and luminescent properties of Zn_7In_(2-x)M_xO_10 (M = Ga or Al; 0 <= x <= 1) oxides has been investigated by means of high spatial resolution X-ray spectroscopy and high-angle annular dark-field images, combined with magic angle spinning nuclear magnetic resonance spectroscopy. Local structural variations have been identified for the Al- and Ga-doped samples through the analysis of atomically resolved chemical maps and the identification of their structural environment within the wurtzite lattice. In3+ is distributed in a zig-zag modulation, while Al^(3+) and Ga^(3+) are located in a flat distribution at the center of the wurtzite block. Density functional theory calculations provide unambiguous evidence for the preferential flat location of Ga^(3+) and Al^(3+) associated with the different strains introduced in the structure as a result of their ionic radii. The characterization of the photoluminescence response reveals the appearance of new radiative recombination pathways for the doped materials because of the presence of new defect levels in the band gap of the Zn_7In_2O_10 structure.Item Effect of the synthesis method on the properties of lithium doped graphene oxide composites with tin oxide nanoparticles: Towards white luminescence(Journal of physics and chemistry of solids, 2019) Prado Hurtado, Félix del; Taeño González, María; Maestre Varea, David; Ramírez Castellanos, Julio; González Calbet, José María; Cremades Rodríguez, Ana IsabelGraphene oxide (GO) based composites functionalized with nanoparticles are emerging as potential candidates for multifunctional devices. As the synthesis route can strongly influence the way in which the nanoparticles are anchored to GO and the resulting properties, different routes have been employed and evaluated in this work for the preparation of composites formed by GO and undoped or Li doped SnO_2 nanoparticles. Promotion of synergetic effects, as well as changes in the structural and luminescent properties of the composites have been also analyzed. In comparison with GO, composite samples synthesized in this work involve enhanced luminescence while retaining nearly white emission, which could lead to wider applicability of GO based composites in free standing and emitting and sensing devices. Aspects, such as GO reduction, stabilization of different Sn-based oxides, variation in the concentration of oxygen related functional groups, changes in the sp^2 domain sizes, incorporation of lithium and enhancement of the luminescence, have been analyzed in this work by means of xray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), energy dispersive x-ray spectroscopy (EDS), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) characterizations.Item Influence of doping and controlled sn charge state on the properties and performance of SnO nanoparticles as anodes in li-ion batteries(Journal of physical chemistry C, 2020) Vázquez López, Antonio; Maestre Varea, David; Ramírez Castellanos, Julio; González Calbet, José María; Pís, Igor; Nappini, Silvia; Yuca, Neslihan; Cremades Rodríguez, Ana IsabelLi-ion batteries (LiB) play nowadays a major role in several technological fields. In addition to enhanced high capacity and long cyclability, some other issues regarding safety, materials sustainability, and low cost remain unsolved. Tin oxide (SnO_2) presents several of those advantages as an anode material; however, some aspects still require to be investigated such as capacity fading over cycles. Herein, tin oxide nanoparticle-based anodes have been tested, showing high capacities and a significant cyclability over more than 150 cycles. A complementary strategy introducing doping elements such as Li and Ni during the synthesis by hydrolysis has been also evaluated versus the use of undoped materials, in order to assess the dependence on SnO_2 quality and properties of battery performance. Diverse aspects such as the Sn charge state in the synthesized nanoparticles, the variable incorporation of dopants, and the structure of defects have been considered in the understanding of the obtained capacity.