Organic materials capable of emission in the near infrared (NIR) spectral range are of great interest for many branches of science and technology. In this work we investigate a NIR emitting molecule (DTDPAB) based on 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) modified with nitrogen substitution at the carbon meso position (AZABODIPY) and thiophens and phenyls substituents. The thienyl substituents decrease the energy band gap of the molecule with respect to standard AZABODIPY and the emission spectrum results strongly shifted to the lower energies. The molecule is employed as a dopant in commercial and suitably synthesized polymers used as hosts in solution-processable emitting layers of organic light-emitting diodes (OLEDs). After device architecture optimization the electroluminescence in pure NIR (> 700 nm) with the maximum at 910 nm is achieved. To our knowledge, this is the first example of electroluminescence from a single AZABODIPY emitter in real NIR, which adds another type of electrically excitable organic luminophore to the family of NIR emitting materials.

Substitution of the chlorido ligand of cyclometalated [Pt (5-R-1,3-di(2-pyridyl) benzene)Cl] (R = methyl, mesityl, 2-thienyl, or 4-diphenylamino-phenyl) by 4-phenylthiazole-2-thiolate leads to related thiolato complexes, which were fully characterized. Their photophysical properties were determined in degassed dichloromethane solution. The emission color of the novel complexes can be easily tuned by the nature of the substituents on the terdentate ligand, as is the case for the parent chlorido complexes. Their luminescence Quantum Yield is high, with that of the compounds with the 2-thienyl or 4-diphenylamino-phenyl substituents being much higher than that of the related chloride complexes. The platinum complex with the cyclometalated 5-(2-thienyl)-1,3-di(2-pyridyl) benzene was used as the emitter for the fabrication of a yellow solution-processable OLED.

The preparation and characterization of three new complexes, namely [Pt(1,3-bis(4-triphenylamine-pyridin-2-yl)-4,6-difluoro-benzene)Cl] ([PtL1Cl]), [Pt(1,3-bis(4-triphenylamine-pyridin-2-yl)-5-triphenylamine-benzene)Cl] ([PtL2Cl]), and [Pt(1,3-bis(4-triphenylamine-pyridin-2-yl)-5-mesityl-benzene)Cl] ([PtL3Cl]), is reported. All of them are highly luminescent in dilute deaerated dichloromethane solution (?lum = 0.88-0.90, in the yellow-green region; the ?max,em in nm for the monomers are: 562, 561 and 549 for [PtL1Cl], [PtL2Cl] and [PtL3Cl], respectively).[PtL1Cl] is the most appealing, being characterized by a very long lifetime (103.9 ?s) and displaying intense NIR emission in concentrated deaerated solution (?lum = 0.66) with essentially no "contamination" by visible light < 600 nm. This complex allows the fabrication of both yellow-green and deep red/NIR OLEDs; OLED emissions are in the yellow-green (CIE = 0.38, 0.56) and deep red/NIR (CIE = 0.65, 0,34) regions, for [PtL1Cl] 8 wt% (with 11% ph/e EQE) and pure [PtL1Cl] (with 4.3% ph/e EQE), respectively.

The energy gap law (E-G-law) and aggregation quenching are the main limitations to overcome in the design of near-infrared (NIR) organic emitters. Here, we achieve unprecedented results by synergistically addressing both of these limitations. First, we propose porphyrin oligomers with increasing length to attenuate the effects of the E-G -law by suppressing the non-radiative rate growth, and to increase the radiative rate via enhancement of the oscillator strength. Second, we design side chains to suppress aggregation quenching. We find that the logarithmic rate of variation in the non-radiative rate vs. E-G is suppressed by an order of magnitude with respect to previous studies, and we complement this breakthrough by demonstrating organic light-emitting diodes with an average external quantum efficiency of similar to 1.1%, which is very promising for a heavy-metal-free 850nm emitter. We also present a novel quantitative model of the internal quantum efficiency for active layers supporting triplet-to-singlet conversion. These results provide a general strategy for designing high-luminance NIR emitters. Light-emitting diodes: Near-infrared fluorescence from organic moleculesOrganic (carbon-based) light-emitting diodes (LEDs) that emit near-infrared light can be built by linking together large organic molecules called porphyrins, offering many potential industrial and medical applications. Organic near-infrared LEDs have several advantages over conventional LEDs based on inorganic semiconductors, including mechanical flexibility, biocompatibility and the absence of polluting heavy metals. Researchers in the UK and Italy led by Harry Anderson at the University of Oxford and Franco Cacialli at University College London explored the potential of linked porphyrin structures that fluoresce at near-infrared wavelengths. The optical properties of the materials are improved by engineering the molecular structure and a quantitative model is presented to explain the efficient emission. This research provides understanding of exciton dynamics and points towards innovative uses of near-infrared light in applications including light therapy, optical communications, biosensors and biometric systems.

The preparation and characterization of a new platinum(ii) complex bearing a N^C^N-cyclometalating ligand and a thiolate coligand, namely 5-mesityl-1,3-di-(2-pyridyl)benzene and 1-phenyl-1H-tetrazole-5-thiolate, is reported. Its structure is determined by X-ray diffraction studies on a single crystal. This new complex exhibits green and red phosphorescence in dichloromethane solution (?lum = 0.90) and in the solid state (?lum = 0.62), respectively. In both cases the quantum yield is impressive showing for the first time that N^C^N platinum(ii) complexes with a suitable thiolate coligand can reach outstanding luminescence properties. The excellent solubility of this complex allows fabrication of green processable solution-OLEDs with maximum EQE similar to that obtained with more expensive vacuum techniques and, depending on its concentration, one can tune the color of the OLED. The molecular geometry, ground state, electronic structure, and excited electronic states of the complex, both as a monomer and dimer aggregate in solution, are calculated by density functional theory (DFT) and time-dependent DFT approaches, giving insight into the electronic origin of the absorption spectra. Remarkably, the dimer is less sensitive to oxygen quenching than the monomer because the two 1-phenyl-1H-tetrazole fragments protect the platinum(ii) centers, as suggested by a combination of luminescence studies and theoretical calculations.

A layered hybrid perovskite belonging to the <110> series, (FA)(HEA)PbBr (HEA, hydroxyethylammonium; FA, formamidinium) exhibits a bright green narrow emission and a reversible mechanochromic luminescence effect: after grinding the powder a few seconds, the emission is blue shifted from 500 to 480 nm due to a partial amorphization. PeLEDs based on (FA)(HEA)PbBr as active material were also demonstrated, which is unprecedented for such a layered hybrid perovskite.

Intrinsically chiral double stapled ortho-oligo phenylene ethynylenes (o-OPEs) 1 show g(lum) values up to 5.5 x 10(-2), the second highest value ever observed for a simple organic molecule (SOM). DFT calculations of molecular spectra and properties encompassing electric and magnetic dipole transition moments account for these observations.

The electroluminescence test is an experiment typically used to verify the behavior of the photovoltaic cell and to qualitatively check its integrity. It works by operating the photovoltaic cell as a diode polarized directly: the cells that light up in a module indicate how many of them work. This test provides an estimate of the maximum performance of the entire photovoltaic module. A qualitative inspection was performed by electroluminescence tests on 48 modules of photovoltaic cells. They had already been installed on a small-size concentration solar plant before the test and some modules had reached a lower level of performance than expected. A first electroluminescence test was performed, which showed that only 61.5% of the photocells worked. Since there were visible signs of humidity within the various modules, some of the inoperative modules underwent a dehumidification treatment in a climatic chamber. A second electroluminescence test showed that the percentage of functioning cells had increased to 66.3% after the drying treatment.

Thanks to their highly tunable band gaps, graphene nanoribbons (GNRs) with atomically precise edges are emerging as mechanically and chemically robust candidates for nanoscale light emitting devices of modulable emission color. While their optical properties have been addressed theoretically in depth, only few experimental studies exist, limited to ensemble measurements and without any attempt to integrate them in an electronic-like circuit. Here we report on the electroluminescence of individual GNRs suspended between the tip of a scanning tunneling microscope (STM) and a Au(111) substrate, constituting thus a realistic optoelectronic circuit. Emission spectra of such GNR junctions reveal a bright and narrow band emission of red light, whose energy can be tuned with the bias voltage applied to the junction, but always lying below the gap of infinite GNRs. Comparison with ab initio calculations indicates that the emission involves electronic states localized at the GNR termini. Our results shed light on unpredicted optical transitions in GNRs and provide a promising route for the realization of bright, robust, and controllable graphene-based light-emitting devices.

Nitrogen-vacancy centers hi diamond are considered to be promising building blocks for emerging quantum technologies. At the same tine, practical applications require them to be excited and controlled electrically. However, there is a lack of knowledge about their behavior in electrical driven systems. here, we introduce a physical model to address the single-photon emission dynamics of electrically pumped NV center in diamond in a quantitative manner and present a detailed study of the single-photon emitting diode based on NV centers.

Low-power, high-speed, and bright electrically driven true single-photon sources, which are able to operate at room temperature, are vital for the practical realization of quantum-communication networks and optical quantum computations. Color centers in semiconductors are currently the best candidates; however, in spite of their intensive study in the past decade, the behavior of color centers in electrically controlled systems is poorly understood. Here we present a physical model and establish a theoretical approach to address single-photon emission dynamics of electrically pumped color centers, which interprets experimental results. We support our analysis with self-consistent numerical simulations of a single-photon emitting diode based on a single nitrogen-vacancy center in diamond and predict the second-order autocorrelation function and other emission characteristics. Our theoretical findings demonstrate remarkable agreement with the experimental results and pave the way to the understanding of single-electron and single-photon processes in semiconductors.

The interconnection layer (ICL) of organic multijunction solar cells represents one of the most delicate parts to ensure an efficient device operation. In view of pushing the efficiencies toward the theoretical limit, the individuation of minor losses affecting the ICL operation is of crucial importance. However, the difficulties arising from its position within the complex device structure typically hamper an accurate and selective investigation of the ICL. Here, a method based on the analysis of the photo-generated current density-voltage (Jph-V) response of solar cells, in the region of bias over the open-circuit voltage, is proved to individuate minor electrical losses within the ICL. Interestingly, the proposed method is demonstrated to effectively operate on tandem substructures, where different ICLs are investigated through the combination of materials having diverse characteristics. Furthermore, the use of a complementary investigation technique based on electroluminescence (EL) analysis allows to distinguish the specific nature of the electrical losses. The combination of Jph-V and EL analyses represents an elegant and advanced approach to shed light on the quality of ICLs in tandem substructures by avoiding the fabrication of the more complex tandem architecture.

This review reports on a new process for the synthesis of Si nanowires (NWs), based on the wet etching of Si substrates assisted by a thin metal film. The approach exploits the thicknessdependent morphology of the metal layers to define uncovered nanometric Si regions, which behave as precursor sites for the formation of very dense (up to 1. x. 10(12) NW cm(-2)) arrays of long (up to several mu m) and ultrathin (diameter of 5-9 nm) NWs. Intense photoluminescence (PL) peaks, characterized by maxima in the 640-750 nm range and by an external quantum efficiency of 0.5%, are observed when the Si NWs are excited at room temperature. The spectra show a blueshift if the size of the NW is decreased, in agreement with the occurrence of quantum confinement effects. The same etching process can be used to obtain ultrathin Si/Ge NWs from a Si/Ge multi-quantum well. The Si/Ge NWs exhibit-in addition to the Si-related PL peak-a signal at about 1240 nm due to Ge nanostructures. The huge surface area of the Si NW arrays can be exploited for sensing and analytical applications. The dependence of the PL intensity on the chemical composition of the surface indeed suggests interesting perspectives for the detection of gaseous molecules. Moreover, Si NWs decorated with Ag nanoparticles can be effectively employed in the interference-free laser desorption-ionization mass spectrometry of lowmolecular-weight analytes. A device based on conductive Si NWs, showing intense and stable electroluminescence at an excitation voltage as low as 2 V, is also presented. The unique features of the proposed synthesis (the process is cheap, fast, maskless and compatible with Si technology) and the unusual optical properties of the material open the route towards new and unexpected perspectives for semiconductor NWs in photonics.

The recently demonstrated electroluminescence of color centers in diamond makes them one of the best candidates for room temperature single-photon sources. However, the reported emission rates are far off what can be achieved by state-of-the-art electrically driven epitaxial quantum dots. Since the electroluminescence mechanism has not yet been elucidated, it is not clear to what extent the emission rate can be increased. Here we develop a theoretical framework to study single-photon emission from color centers in diamond under electrical pumping. The proposed model comprises electron and hole trapping and releasing, transitions between the ground and excited states of the color center as well as structural transformations of the center due to carrier trapping. It provides the possibility to predict both the photon emission rate and the wavelength of emitted photons. Self-consistent numerical simulations of the single-photon emitting diode based on the proposed model show that the photon emission rate can be as high as 100 kcounts s(-1) at standard conditions. In contrast to most optoelectronic devices, the emission rate steadily increases with the device temperature achieving of more than 100 Mcount s(-1) at 500 K, which is highly advantageous for practical applications. These results demonstrate the potential of color centers in diamond as electrically driven non-classical light emitters and provide a foundation for the design and development of single-photon sources for optical quantum computation and quantum communication networks operating at room and higher temperatures.

We show that iridium complexes incorporating a tetrazolate ligand can be used as new highly phosphorescent emitters in the fabrication of high-efficiency organic light emitting devices (OLEDs). The nature of the excited states of these Ir(iii) complexes was probed by means of electrochemical analysis, absorption and photoluminescence spectroscopies and with the aid of TD-DFT calculations. To demonstrate the high stability of these classes of complexes we used TGA and DSC characterizations. These complexes are used as dopant emitters in the emissive layers. The as-fabricated OLEDs display high-efficiency and high-brightness with blue, green and yellow/orange emission.

Organic light emitting diodes (OLEDs) operating in the near-infrared spectral region are gaining growing relevance for emerging photonic technologies, such as lab-on-chip platforms for medical diagnostics, flexible self-medicated pads for photodynamic therapy, night vision and plastic-based telecommunications. The achievement of efficient near-infrared electroluminescence from solution-processed OLEDs is, however, an open challenge due to the low photoluminescence efficiency of most narrow-energy-gap organic emitters. Diketopyrrolopyrrole-boron complexes are promising candidates to overcome this limitation as they feature extremely high photoluminescence quantum yield in the near-infrared region and high chemical stability. Here, by incorporating suitably functionalized diketopyrrolopyrrole derivatives emitting at similar to 760 nm in an active matrix of poly(9,9-dioctylfluorene-alt-benzothiadiazole) and without using complex light out-coupling or encapsulation strategies, we obtain all-solution-processed NIR-OLEDs with external quantum efficiency as high as 0.5%. Importantly, our test-bed devices show no efficiency roll-off even for high current densities and high operational stability, retaining over 50% of the initial radiant emittance for over 50 hours of continuous operation at 10 mA/cm(2), which emphasizes the great applicative potential of the proposed strategy.

The irreversible reaction of methyl triflate with neutral Re(I) tetrazolato complexes of the type fac-[Re(diim)(CO)3(L)], where diim is either 1,10-phenanthroline or 2,2?-bipyridine and L is a para substituted 5-aryltetrazolate, yielded the corresponding cationic methylated complexes. While methylation occurred regioselectively at the N4 position of the tetrazole ring, the cationic complexes were found to exist in solution as equilibrating mixtures of linkage isomers, where the Re(I) centre was bound to either the N1 or N2 atom of the tetrazole ring. The existence of these isomers was highlighted both by NMR and X-ray crystallography studies. On the other hand, the two isomers appeared indistinguishable by IR, UV-Vis and luminescence spectroscopy. The prepared cationic complexes are all brightly phosphorescent in fluid and rigid solutions, with emission originating from triplet metal-to-ligand charge transfer excited states. Compared to their neutral precursors, which emit from admixtures of triplet metal-to-ligand and ligand-to-ligand charge transfer states, the methylated complexes exhibit blue-shifted emission characterised by elongated excited state lifetimes and increased quantum yields. The nature of the excited states for both the neutral and the methylated complexes was probed by resonance Raman spectroscopy and with the aid of time-dependent density functional theory calculations. Lastly, both the neutral and the methylated species were used as emitting phosphors in the fabrication of Organic Light Emitting Diodes and Light Emitting Electrochemical Cells.

Two new pincer proligands, namely 5-(p-(N, N-diphenylamino) phenylethynyl)-1,3-di(2-pyridyl) benzene (HL1) and trans-5-(p-(N, N-diphenylamino) styryl-1,3-di(2-pyridyl) benzene (HL2) were prepared together with their N boolean AND C boolean AND N-coordinated cyclometallated platinum(II) complexes (PtLX)-X-1 (X = Cl, NCS) and (PtLCl)-Cl-2. Both ligands are intensely luminescent in solution (quantum yields > 0.8). (PtLX)-X-1 complexes display high quantum yields in solution whereas that of (PtLCl)-Cl-2 is very low due to the ease with which trans to cis isomerisation of the diphenylaminostyryl C=C bond occurs. Distinct sets of emission bands attributable to the cis and trans forms are observable in glass at 77 K, the assignments being supported by TD-DFT calculations. Organic light-emitting diodes (OLEDs) have been prepared using the new compounds as phosphorescent emitters. Remarkably, despite the inferior quantum yield of (PtLCl)-Cl-2 in solution, the best electroluminescence quantum efficiencies are obtained with this complex, which emerges as an excellent candidate for the preparation of NIR-OLEDs.

The emission color from colloidal semiconductor nanocrystals (NCs) is usually tuned through control of particle size, while multicolor emission is obtained by mixing NCs of different sizes within an emissive layer. Here, we demonstrate that recently introduced "dot-in-bulk" (DiB) nanocrystals can emit two-color light under both optical excitation and electrical injection. We show that the effective emission color can be controlled by adjusting the relative amplitudes of the core and shell emission bands via the intensity of optical excitation or applied bias in the cases of photoluminescence (PL) and electroluminescence (EL), respectively. To investigate the role of nonradiative carrier losses due to trapping at intragap states, we incorporate DiB NCs into functional light-emitting diodes and study their PL as a function of applied bias below the EL excitation threshold. We show that voltage-dependent changes in core and shell emissions are not due to the applied electric field but rather arise from the transfer of charges between the anode and the NC intragap trap sites. The changes in the occupancy of trap states can be described in terms of the raising (lowering) of the Fermi level for reverse (direct) bias. We find that the applied voltage affects the overall PL intensity primarily via the electron-trapping channel while bias-induced changes in hole-trapping play a less significant role, limited to a weak effect on core emission. © 2013 American Chemical Society.

We investigated the nature of the emissive states in newly synthesized cyclometallated Pt complexes containing a chelating 2-pyridyl tetrazolate (2-PTZ) ligand, namely Pt(ppy)(2-PTZ), and Pt(F2ppy)(2-PTZ) as a solid-state phosphor, by examining their structural properties versus their phosphorescence (PH) and electroluminescence (EL) characteristics. It is found that the observed tuning of both PH and EL spectra, their red shift and shortening decay with increasing concentration in the complex blends are due to the competition between three emissive states: monomer, excimer and dimer. The pure dimer emission appeared in neat films, reaching a high PH quantum yield of about 75% and external EL efficiency approaching 10% for the OLED based on the neat Pt(F2ppy)(2-PTZ) complex film as an emitting layer (EML). X-ray diffraction proved the high structural order of the latter thin film. These findings have a direct impact on the design of a new OLED generation based on single phosphor multiemission controlled by the structural order degree of the EML.