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.

The improvement of photocatalytic activity of TiO2-based nanomaterials is widely investigated due to the tentative of their industrialization as environmental photocatalysts and their inherently low solar spectrum sensitivity and rapid recombination of charge carriers. Coupling of oxygen-based bidentate diketone to nanocrystalline TiO2 represents a potential alternative for improving the holdbacks. Formation of TiO2-acetylacetone charge transfer complex (CTC) by sol-gel route results in a hybrid semiconductor material with photodegradation activity against toxic NOx gas. In this research, the influence of the chelating agent acetylacetone (ACAC) content on the CTC photocatalytic efficiency under visible light was evaluated. A high content of ACAC in the CTC is not a decisive factor for efficiency of photocatalytic reactions. In fact, the highest efficiency for NOx degradation (close to 100%, during 1 h of visible light exposure) was reported for the material calcined in air at 300 °C with the content of strongly bonded acetylacetone not higher than 3 wt.%. Higher calcination temperature (400 °C) left TiO2 almost completely depleted in ACAC, while at the highest applied temperature (550 °C) a portion of anatase was transformed into rutile and the sample is free of ACAC. The analyses pointed out that superoxide anion radical (O2−) plays an active role in photo-oxidation of NOx. Our findings indicate that this CTC has both high visible light spectral sensitivity and photocatalytic efficiency.

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