Examinando por Autor "Álvarez, Ángel Luis"

Mostrando 1 - 4 de 4

Highly efficient solution-processed white organic light-emitting diodes based on novel copolymer single layer
(Elsevier, 2012) Coya, Carmen; Álvarez, Ángel Luis; Ramos, Mar; Gómez, Rafael; Seoane, Carlos; Segura, José Luis
We fabricate by solution processed methods organic light emitting diodes with single-layer structure (ITO/(PEDOT:PSS)/co-polymer/Ba/Al) and study the transport properties of the final devices. The copolymer is novel poly(fluorene-alt-phenylene) (PFP) derivatives containing co-monomers, involving red-emitting 1,8-naphthalimide units as pendant groups (0.0005, 0.005, 0.02 and 0.08 wt%) covalently attached. All the devices exhibited emission at very low driving currents in the A range (47¿73 A). White emission with luminous efficiency of 9.42 Cd/A at 50 A is obtained for the co-polymer with the smallest amount of chromophore. Commission Internationale de L¿Eclairage (CIE) coordinates evolve from almost pure white color (0.26, 0.30) for low currents to stable cool white (0.21, 0.23). Increasing naphthalimide contents leads to stable green and orange emission with 3.07, 19.5 and 6.7 Cd/A efficiencies. The current-voltage response of the devices is analyzed by means of a numerical model that includes an injection mechanism based in the microscopic hopping theory and a field-dependent carrier mobility for the bulk transport regime. The fitting results allow to estimate the dependence of carrier mobility on polymer composition in the diodes.
Novel erbium(III) fluorinated b-diketonate complexes with N,N-donors for optoelectronics: from synthesis to solution-processed devices+
(Royal Society of Chemistry, 2013) Martín-Ramos, Pablo; Ramos Silva, Manuela; Coya, Carmen; Zaldo, Carlos; Álvarez, Ángel Luis; Álvarez-García, Susana; Matos Beja, Ana M.; Martín-Gil, Jesús
Three novel ternary Er3+ complexes emitting in the C band transmission window for fiber optic communications have been synthesised and their structures have been elucidated by single crystal X-ray diffraction. The fluorinated b-diketonate ligand, 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione, combines a good absorption cross-section in the ultraviolet region with reduction of non-radiative quenching of the Er3+ emission, while the rigidity and bulkiness of the three different N,N-donors (2,20-bipyridine, bathophenanthroline and 5-nitro-1,10-phenanthroline) have a pronounced impact on the emission intensity of luminescence. Furthermore, the choice of the ancillary ligand also determines the efficiency of the antenna effect, leading to complete quenching of the ligand-associated visible emission for the optimized complex with 5-nitro-1,10-phenanthroline. Solution processed 1.54 mm organic light-emitting diodes have been manufactured and characterized for this complex, confirming the aforementioned complete resonant energy transfer from the ligands to the Er3+ ion. The features of the reported device fabrication show a simple way to obtain large area NIR-OLEDs.
Star-shaped hexaaryltriindoles small molecules: Tuning molecular properties towards solution processed organic light emitting devices
(Elsevier, 2012) Coya, Carmen; Ruiz, Constanza; Álvarez, Ángel Luis; Álvarez-García, Susana; García-Frutos, Eva M.; Gómez-Lor, Berta; Andrés, Alicia de
We present a series of differently substituted star-shaped hexaaryltriindoles with tunable light-emitting properties. The deep blue emission is unchanged by donor peripheral substituents while an increasing acceptor character produces a reduction of the optical gap, an increased Stokes shift and eventually leads to the appearance of a new electronic level and to the simultaneous deep blue (413 nm) and green (552 nm) emission in solution. Quenching by concentration increases with the acceptor character but is lower as the tendency of these compounds to aggregate is stronger. Solution processed thin films present optical and morphological qualities adequate for device fabrication and similar electronic structure compared to solutions with an emission range from 423 nm up to 657 nm (red), demonstrating the possibility of tuning the energy levels by chemical functionalization. We have fabricated and characterized single-layer solution processed organic light emitting diodes (OLED) to investigate the influence on transport and emission properties of the substituting species. We analyzed the I¿V response using a single-carrier numerical model that includes injection barriers and non-uniform electric-field across the layer. As a result, we obtained the electric field dependence of the mobility for each device. Best results are obtained on the most electron rich derivative functionalized with six donor methoxy groups. This material shows the highest emission efficiency in solid state, due to aggregation-induced enhancement, and better transport properties with the highest mobility and a very low turn-on voltage of 2.8 V. The solution processed OLED devices produce stable deep blue (CIE coordinates (0.16, 0.16)) to white (CIE coordinates (0.33, 0.3)) emission with similar luminous efficiencies.
Synthesis and tunable emission of novel polyfluorene co-polymers with 1,8-naphthalimide pendant groups and application in a single layer-single component white emitting device
(ELSEVIER, 2010-08) Juárez, Rafael; Coya, Carmen; Blanco, Raúl; Gómez, Rafael; Martínez, Rocío; Andrés, Alicia de; Álvarez, Ángel Luis; Zaldo, Carlos; Ramos, María M.; Peña, Alejandro de la; Seoane, Carlos; Segura, José L.
New luminescent polymers containing two individual emission species-poly(fluorene-alt-phenylene) as a blue host and variable amounts of 1,8-naphthalimide as red dopant have been designed and synthesized. Optical studies (optical absorption (OA) and steady-state photoluminescence emission (PL)) in diluted solutions and thin solid films reveal that the emission spectrum can be tuned by varying the content of 1,8-naphthalimide moieties. Although no significant interaction can be observed between both moieties in the ground state, after photoexcitation an efficient energy transfer takes place from the PFP backbone to the red chromophore, indeed, by adjusting the polymer/naphthalimide ratio it is possible to obtain single polymers which emit white light to the human eye in solid state. Energy transfer is more effective in the co-polymers than in physical mixtures of the two chromophores. We prepared single-layer electroluminescent simple devices with structure: ITO/poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT:PSS)/active layer/Ba/Al. With this single layer¿single component device structure, white light with Commission Internationale de l¿Eclairage (CIE) color coordinates (0.3, 0.42) is obtained for the electroluminescence (EL) emission with an efficiency of 22.62 Cd/A.