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The development of near-infrared (NIR) photodetection technologies is driven by emerging applications such as medical imaging or optical sensors for electronic displays and machine vision. An all-organic upconverter (OUD) is a device that converts incident NIR light directly into visible light and consists of a monolithic stack of a NIR organic photodetector (OPD) and a visible organic light-emitting diode (OLED). We present OUDs that consist of NIR heptamethine cyanine dyes/C60 fullerene OPDs and a fluorescent tris(8-hydroxyquinolinato)aluminium (Alq3) OLED. The device metrics of performance are a high external quantum efficiency (EQE) of 43% of the OPD part and an OUD luminance turn-on at low bias voltages of 2 V. The dynamic response of the photocurrent and luminance is linear over a NIR light range corresponding to 26 dB. These OUDs upconvert NIR light at 830 nm to green light with a photon-to-photon conversion efficiency of 0.61%, close to the expected maximum.

The synthesis of a phenoxy-benzothiadiazole (BTD) derivative is reported for the first time. This derivative was employed as an intermediate in the obtention of two novel highly fluorescent aryl-phenoxy-BTD dyes. Their photophysical properties were evaluated in solution and the results indicate a strong intramolecular charge transfer (ICT) character in the excited state. The luminophore 3a, possessing a donor-BTD-phenoxide architecture, exhibits superior fluorescence quantum yield (0.67) than the designed acceptor-BTD-phenoxide dye (0.06). After electrochemical and photoluminescence characterization of thin films of 3a, an OLED with the configuration ITO/PEDOT:PSS/3a/TPBi/LiF/Al was constructed. This device displayed a green emission centered at 547 nm, with CIE coordinates of (0.40, 0.55). For comparison, an OLED using a previously reported luminescent BTD-pyridyl derivative was also constructed. The OLED made with the phenoxy-BTD derivative operated using less current density and led to higher irradiance and electrical stability, indicating the high potential of ArO-BTD dyes for future application in electroluminescent devices.

An in situ reaction of two optoelectronically active organic ligands (anionic thenoyltrifluoroacetylacetone, tta−, and neutral triphenylphosphine oxide, tppo) with erbium(III) ion in the presence of a base yielded a new erbium complex, [Er(tta)3(tppo)]. The solid and solution structure of the complex was established by X-ray crystallography, NMR, ESI-MS, FTIR, TGA and Raman spectroscopy. They indicate that the Er(III) ion is coordinated to seven oxygen atoms of three tta ligands and one tppo ligand in a monocapped octahedral geometry. The Judd–Ofelt parameters of the complex were determined by a least squares fitting and dealt with its chemical structure. On UV excitation through ligand mediation, the complex shows the characteristic near-infrared emission of the corresponding Er(III) ion at 1534 nm. Furthermore, a near infra-red organic light emitting diode (NIR-OLED) was fabricated with structure: ITO/[N,N′-bis(naphthalen-2-yl)-N,N′-bis(phenyl)benzidine]/[Er(tta)3(tppo)]/[2,2′,2′′-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)]/LiF/Al. This device, with maximum applied voltage of 23 V, shows a total quenching of visible emission and electroluminescence in the C-band region (1534 nm) which is suitable for third communication window applications in fiber optics. Finally, an organic diode was fabricated to determine charge carrier mobility of the complex using a steady-state method.

A series of NIR emitting novel ytterbium tris β-diketonate ternary complexes, [Yb(tta) 3 (L)]·H 2 O {tta = thenoyltrifluoroacetylacetone and L = dibenzyl sulphoxide (dbso), diphenyl sulphoxide (dpso) and benzoguinamine (bga)} was synthesised, and the photophysical and optoelectronic properties of their films were studied. Nuclear Magnetic Resonance (NMR) analysis indicates that the complexes are seven-coordinate which is a highly asymmetric structure enhancing the radiative transitions. It is an indicative of efficient energy transfer from coordinated ligands to Yb ion. The complexes were doped in Tris(4-carbazoyl-9-ylphenyl)amine (TcTa) organic matrix and the doped samples were used as the emitting layers to fabricate near-infrared organic light emitting diodes (NIR-OLEDs) with the structure: Indium tin oxide/{N,N′-bis(naphtalen-2-yl)-N,N′-bis(phenyl) benzidine} (25 nm)/[Yb-complexes] (10%): TcTa (40 nm)/(2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline) (15 nm)/tris(8-hydroxy-quinolinato) aluminium (10 nm)/LiF (0.5 nm)/Al (120 nm). The complex, [Yb(tta) 3 (dpso)]·H 2 O shows the highest electroluminescence (EL) efficiency with maximum irradiance of 22.48 μW/cm 2 and current density of 29.5 mA/cm 2 at 15 V. It indicates an improved EL performance over the reported devices based on the Yb (III) complexes. In view of electrical characteristics, the current-voltage responses were interpreted by using Mott–Gurney model which allows us to determine the carrier mobility of the complexes.

Hydrazones constitute a class of compounds presenting azomethine R′R″N N CH R hydrogens, which show diverse properties and a wide range of applications. A hydrazone derived from the antituberculosis drug isoniazid, namely, N,N′-diisonicotinoyl-2-hydroxy-5-methylisophthalaldehyde hydrazone (DMD) was synthesized and chemically characterized. Its luminescent properties were also investigated, as well as the possibility of using this compound as a constituent of the emitting layer for the fabrication of OLEDs. Co-deposited devices were fabricated using the organic molecule BSBF as matrix and DMD as dopant. All the devices presented a broad electroluminescence band, in which it was possible to recognize the DMD emission along with emissions of some of the other organic layers. The best results were obtained with 35% DMD doping, achieving a luminance of about 35 cd/m2.

In this study, a novel type of tris(2-acyl-1,3-indandione)-aluminum(III) coordination compounds of the general formula [Al(acind)3]H2O, where 2-acyl-1,3-indandione (acind), 2-acetyl-1,3-indandione (aind), 2-benzoyl-1,3-indandione (bind), and 4-methyl-2-benzoyl-1,3-indandione (mbind), were synthesized and characterized by elemental analysis (CHN), Fourier transform infrared (FTIR) and nuclear magnetic resonance (1H NMR) spectroscopies, thermal analysis (TG/DTG and DTA), and optical absorption spectroscopy in the UV-Vis region. These compounds present remarkably high green luminescence in powder and in thin-film forms. However, when these compounds are applied in glass/ITO/β-NPB/spiro-2CBP/[Al(acind)3]/Al and glass/ITO/β-NPB/[Al(acind)3]/LiF/Al electroluminescent devices, where spiro-2CBP is 2,7-bis(carbazol-9-yl)-9,9-spirobifluorene and β-NPB is N,N’-bis(naphthalen-2-yl)-N,N’-bis(phenyl)-benzidine, the emission color tuned from green to red, reflecting a change from the direct charge recombination in the emitting layer of the [Al(acind)3] complexes to an exciplex-based emission in which [Al(acind)3] complexes and spiro 2-CBP acted as acceptor and donor, respectively. These results suggest that [Al(acind)3] complexes have potential applications as molecular light converter materials for fabricating new electroluminescent devices.

Efficient light detection in the near-infrared (NIR) wavelength region is central to emerging applications such as medical imaging and machine vision. An organic upconverter (OUC) consists of a NIR-sensitive organic photodetector (OPD) and an visible organic light-emitting diode (OLED), connected in series. The device converts NIR light directly to visible light, allowing imaging of a NIR scene in the visible. Here, we present an OUC composed of a NIR-selective squaraine dye-based OPD and a fluorescent OLED. The OPD has a peak sensitivity at 980 nm and an internal photon-to-current conversion efficiency of ∼100%. The OUC conversion efficiency (0.27%) of NIR to visible light is close to the expected maximum. The materials of the OUC multilayer stack absorb very little light in the visible wavelength range. In combination with an optimized semitransparent metal top electrode, this enabled the fabrication of transparent OUCs with an average visible transmittance of 65% and a peak transmittance of 80% at 620 nm. Visibly transparent OUCs are interesting for window-integrated electronic circuits or imaging systems that allow for the simultaneous detection of directly transmitted visible and NIR upconverted light.