Neutral benzoquinolate cyclometalated platinum(II) complexes as precursors in the preparation of luminescent Pt-Ag complexes

Complexes [Pt(C6F5)(bzq)(CNR)] {R = tBu (1), 2-naphthyl (2), 2,6-Me2Ph (3)} have been prepared by replacement of the labile acetone in [Pt(C6F5)(bzq)(Me2CO)] with the corresponding isocyanide ligand. The structures 1 and 3 (X-ray) confirms their square planar geometry, with the bzq ligand coplanar to the metal plane. The reactions of 1-3 toward AgClO4 lead to the trinuclear complexes [{Pt(C6F5)(bzq)(CNR)}2Ag]ClO4 {R = tBu (4), 2-naphthyl (5)} or the tetranuclear [{Pt(C6F5)(bzq)(CN-2,6-Me2Ph)Ag}2](ClO4)2 (6). The structures of these three polynuclear complexes have been established by X-ray diffraction studies. Two pseudo-polymorphs of 4 (4a and 4b), only differing in the crystallization solvent, have been found. 4a/b and 5 are trinuclear Pt-Ag-Pt complexes with a >sandwich> disposition. In all three cases, two >Pt(C6F5)(bzq)(CNR)> fragments are linked by a silver atom through Pt → Ag bonds of donor acceptor nature and the silver center establishes a short η1 interaction with the Cipso of the bzq ligands. Furthermore, the study of the structure of 6 reveals two >(C6F5)(bzq)(CN-2,6-Me2Ph)PtAg> subunits, each containing a Pt → Ag bond related by an inversion center and held together through η2 interactions established by the silver atom of one unit and one of the aromatic rings of the bzq ligand of the other. The reaction of 1-3 with [Ag(OClO3)(PPh3)] produces [(C6F5)(bzq)(CNR)PtAg(PPh3)]ClO4 {R = tBu, (7), 2-naphthyl (8), 2,6-Me2Ph (9)}. These dinuclear clusters contain a Pt → Ag bond and show dynamic processes in solution (NMR) which involve the rupture and formation of these interactions. The X-ray structure of 7 confirms the presence of a Pt-Ag bond and a η1 interaction with the Cipso of the bzq ligand (2.514(6) Å). All the crystal structures determined show π⋯π interactions of the bzq which stack in a parallel fashion with interplanar distances of ca. 3.3-3.4 Å. In 5 and 6 the aromatic fragments of the isocyanide ligands also take part in these π⋯π interactions. Absorption and emission properties of all the complexes 1-9 have been studied and explained with the aid of TD-DFT theoretical calculations. Compounds 1-9 are not emissive in solution but they are in rigid matrix. In glassy 2-Me-THF or CH2Cl2 at 77 K the Pt/Ag compounds 4-9 at any concentration (10- 3 M, 10- 4 M, 10- 5 M) show the same emission spectra as their corresponding starting complexes 1-3, in line with the rupture of the Pt-Ag bonds. In the solid state only the dinuclear compounds [Pt(C6F5)(bzq)(CN-tBu)AgPPh3]ClO4 (7) and [Pt(C6F5)(bzq)(CN-2,6-Me2Ph)AgPPh3]ClO4 (9) together with the tetranuclear complex [{Pt(C6F5)(bzq)(CN-2,6-Me2Ph)Ag}2](ClO4)2 (6) are emissive at room temperature showing bright greenish (7, 9) or yellowish (6) phosphorescence. In all three compounds a significant contribution of M′ orbitals (AgPPh3/Ag) to the frontier orbitals (FO) has been observed, and their main emissions seem to arise from mixed excited states 3ILCT (π-π∗ (bzq))/3MM′LCT (Pt/AgPPh3 → bzq) (7, 9) or 3LMM′CT [(bzq) → Pt/Ag]/3ILCT [π-π∗ (bzq)] (6) in nature.This work was supported by the Spanish MICINN (DGPTC/FEDER) (Project CTQ2008-06669-C02-01/BQU) and MINECO (Projects CTQ2012-35251 and TEC2012-38901-C02-01), and the Gobierno de Aragón (Grupo Consolidado E21: Química Inorgánica y de los Compuestos Organometálicos).Peer Reviewe

Stoichiometry of silicon-rich dielectrics for silicon nanocluster formation

Silicon photonics has been bred by several techniques including Chemical Vapour Deposition (CVD) and ion implantation amongst others in order to synthesize silicon nanoclusters with CMOS-compatible technologies. Most of these techniques end up relying on the formation of nanoclusters through the diffusion and segregation of silicon atoms in a silicon-rich dielectric matrix. In this work we present a parallel analysis on silicon rich dielectric layers obtained by different methods. X-Ray Photoelectron Spectroscopy, ellipsometry and photoluminescence are used to characterize Low Pressure CVD and Plasma Enhanced CVD samples in the same theoretical silicon excess range. The analysis shows that independently on the obtaining method the initial concentration of silicon excess can be used to estimate some properties. The actual binding of the atoms can change as well regardless of their initial quantity. However secondary parameters such as the obtaining temperature and the nitrogen concentration in the layer have to be taken into account. Therefore, experimental parameters such as the flow ratio between reactant gases or the refractive index prove to be insufficient if samples obtained by different methods are compared.</p

White light emission from planar remote phosphor based on NHC cycloplatinated complexes

We report on the generation of bright white luminescence through solid-state illumination of remote phosphors based on novel cycloplatinated N-heterocyclic carbene (NHC) compounds. Following a stepwise protocol we got the new NHC compound [{Pt(μ-Cl)(CC∗)}] (4) (HCC∗-κC∗ = 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1H-imidazol-2-ylidene), which was used together with the related ones 4a (HCC∗-κC∗= 1-(4-cyanophenyl)-3-methyl-1H-imidazol-2-ylidene) and 4b (HCC∗-κC∗= 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene) as starting materials for the synthesis of the new ionic derivatives [Pt(R-CC∗) (CNR′)]PF (R = -COOEt, R′ = t-Bu (5), Xyl (6); R = -CN, R′ = t-Bu (7), Xyl (8); RC = Naph, R′ = t-Bu (9), Xyl (10)). The X-ray structures of 6 and 8-10 have been determined. The photophysical properties of these cationic compounds have been studied and supported by the time-dependent-density functional theory (TD-DFT) calculations. The compounds 5, 8, and 9 have been revealed as the most efficient emitters in the solid state with quantum yields of 41%, 21%, and 40%, respectively. White-light remote-phosphors have been prepared just by stacking different combinations of these compounds and [Pt(bzq) (CN) (CNBu)] (R1) as blue (5, 8), yellow (9), and red (R1) components onto the same substrate. The CCT (correlated color temperature) and the CRI (color rendering index) of the emitted white-light have been tuned by accurately controlling the individual contributions.This work was supported by the Spanish MINECO (Project CTQ2015-67461-P led by Dr. Babil Menjon and Project TEC2012-38901-C02-01, led by Dr. Mariano Peralvarez), the Departamento de Industria e Innovacion del Gobierno de Aragon and Fondo Social Europeo (Grupo Consolidado E21: Quimica Inorganica y de los Compuestos Organometalicos led by Dr. José M. Casas) and Project HI-LED funded by the European Union Seventh Framework Programme (FP7/2007-2013 under grant agreement no. 619912). A. C. acknowledges the support of a FPI grant from the Spanish government.Peer Reviewe

Smart lighting system ISO/IEC/IEEE 21451 compatible

Smart lighting systems go far beyond merely replacing lamps. These modern systems are now able to reproduce arbitrary spectra, color temperatures, and intensities and pivot on smart sensors and actuators incorporating information and communication technologies. This paper presents an interoperable smart lighting solution that combines heterogeneous lighting technologies enabling intelligent functions. The system can shift light intensity to increase visual comfort, and it is oriented toward human centric lighting studies. Moreover, this system follows the guidelines defined by the ISO/IEC/IEEE 21451 standards and ZigBee Light Link and also, it includes an additional transducer signal treatment service for artificial intelligence algorithms. Finally, a representational state transfer application allows us to test the interoperability and visualize energy savings in an office room

Highly efficient platinum-based emitters for warm white light emitting diodes

New cycloplatinated N-heterocyclic carbene (NHC) compounds with chelate diphosphines (P^P) as ancillary ligands, [Pt(R-C^C∗)(P^P)]PF (R-C = Naph, P^P = dppm 1A, dppe 2A, dppbz 3A; R = COEt, P^P = dppm 1B, dppe 2B, dppbz 3B), have been prepared. Their photophysical properties have been extensively studied and supported by the time-dependent-density functional theory (TD-DFT). These compounds show a great thermal stability and a very efficient blue (COEt-C^C∗) or cyan (Naph^C∗) emission in PMMA films (5 wt%), with photoluminescence quantum yield (PLQY) ranging from 53% to 95%. In the solid state, the emission of the Naph^C∗ derivatives becomes orange (1A, 2A) or white (3A, dual blue and yellow emission) due to the operating π-π intermolecular interactions. We have investigated the potential use of these materials for solid-state lighting (SSL) applications. OLEDs with different architectures containing mixtures of 1B and 3A in different ratios as dopants were fabricated. In addition, two-component white light remote phosphors were obtained by stacking different combinations of 1B or 3B as the blue emitter with [Pt(bzq)(CN)(CNXyl)] (R) (bzq = benzoquinolate, Xyl = 2,6-dimethylphenyl) as the red emitter using a 365 nm LED as pumping source. By changing the blue:red ratio, warm white light with optimal CRI and D values and a great range of nominal CCT (4000-2000 K) was obtained.This work was supported by the Spanish Ministerio de Economía y Competitividad (MINECO)/FEDER (Project CTQ2015-67461-P led by Dr Babil Menjón) and by the Gobierno de Aragón and Fondo Social Europeo (Grupo E17_17R: Química Inorgánica y de los Compuestos Organometálicos led by Dr José M. Casas). The authors thank the Instituto de Biocomputación y Física de Sistemas Complejos (BIFI) and Centro de Supercomputación de Galicia (CESGA) for generous allocation of computational resources. U. G. and C. B. acknowledge the support of Project I-Zeb, III Accordo Quadro CNR-Regione Lombardia. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI)

Smart lighting system ISO/IEC/IEEE 21451 compatible

Smart lighting systems go far beyond merely replacing lamps. These modern systems are now able to reproduce arbitrary spectra, color temperatures, and intensities and pivot on smart sensors and actuators incorporating information and communication technologies. This paper presents an interoperable smart lighting solution that combines heterogeneous lighting technologies enabling intelligent functions. The system can shift light intensity to increase visual comfort, and it is oriented toward human centric lighting studies. Moreover, this system follows the guidelines defined by the ISO/IEC/IEEE 21451 standards and ZigBee Light Link and also, it includes an additional transducer signal treatment service for artificial intelligence algorithms. Finally, a representational state transfer application allows us to test the interoperability and visualize energy savings in an office room

Pulsed electroluminescence in silicon nanocrystals-based devices fabricated by PECVD

4 páginas, 5 figuras, 1 tabla.-- PACS: 78.67.Bf.Fully compatible CMOS capacitive devices have been developed in order to obtain electrically stimulated luminescence. By high-temperature annealing in N2 atmosphere PECVD non-stoichiometric silica layers, silicon nanocrystals were formed. Photoluminescence, as well as structural studies, were carried out on these layers to decide the best material composition, which lies next to 17% of silicon excess. Under pulsed electrical stimulation, devices show sharp, narrow, less than 5 μs and pulse-frequency-independent, luminescence peaks at the end of the stimulation pulse. Current analysis on those capacities show hole injection at the beginning and electron injection at the end of the stimulation pulses. It is seen that no positive pulses are needed for attaining bipolar charge injection. Electroluminescence is detected when biasing with negative pulses at about 15 V and increasing up to 50 V. The electroluminescence spectrum matches photoluminescence one, allowing assigning both luminescent radiation to the same emission mechanism, that is, electron–hole recombination within the silicon nanocrystals.This work has been partially supported by the project NANOMAGO: MAT2002-04484, financed by the Spanish Ministry of Education and Science.Peer reviewe

Efficiency and reliability enhancement of silicon nanocrystal field-effect luminescence from nitride-oxide gate stacks

We report on a field-effect light emitting device based on silicon nanocrystals in silicon oxide deposited by plasma-enhanced chemical vapor deposition. The device shows high power efficiency and long lifetime. The power efficiency is enhanced up to 0.1 %25 by the presence of a silicon nitride control layer. The leakage current reduction induced by this nitride buffer effectively increases the power efficiency two orders of magnitude with regard to similarly processed devices with solely oxide. In addition, the nitride cools down the electrons that reach the polycrystalline silicon gate lowering the formation of defects, which significantly reduces the device degradation

Si nanocrystal-based LEDs fabricated by ion implantation and plasma-enhanced chemical vapour deposition

Dept. ElectrònicaAn in-depth study of the physical and electrical properties of Si-nanocrystal-based MOSLEDs is presented. The active layers were fabricated with different concentrations of Si by both ion implantation and plasma-enhanced chemical vapour deposition. Devices fabricated by ion implantation exhibit a combination of direct current and field-effect luminescence under a bipolar pulsed excitation. The onset of the emission decreases with the Si excess from 6 to 3 V. The direct current emission is attributed to impact ionization and is associated with the reasonably high current levels observed in current–voltage measurements. This behaviour is in good agreement with transmission electron microscopy images that revealed a continuous and uniform Si nanocrystal distribution. The emission power efficiency is relatively low, ~10−3%, and the emission intensity exhibits fast degradation rates, as revealed from accelerated ageing experiments. Devices fabricated by chemical deposition only exhibit field-effect luminescence, whose onset decreases with the Si excess from 20 to 6 V. The absence of the continuous emission is explained by the observation of a 5 nm region free of nanocrystals, which strongly reduces the direct current through the gate. The main benefit of having this nanocrystal-free region is that tunnelling current flow assisted by nanocrystals is blocked by the SiO2 stack so that power consumption is strongly reduced, which in return increases the device power efficiency up to 0.1%. In addition, the accelerated ageing studies reveal a 50% degradation rate reduction as compared to implanted structures