Blending organic electron donors and acceptors yields intermolecular charge-transfer states with additional optical transitions below their optical gaps. In organic photovoltaic devices, such states play a crucial role and limit the operating voltage. Due to its extremely weak nature, direct intermolecular charge-transfer absorption often remains undetected and unused for photocurrent generation. Here, we use an optical microcavity to increase the typically negligible external quantum efficiency in the spectral region of charge-transfer absorption by more than 40 times, yielding values over 20%. We demonstrate narrowband detection with spectral widths down to 36 nm and resonance wavelengths between 810 and 1,550 nm, far below the optical gap of both donor and acceptor. The broad spectral tunability via a simple variation of the cavity thickness makes this innovative, flexible and potentially visibly transparent device principle highly suitable for integrated low-cost spectroscopic near-infrared photodetection.

The microstructural, optical and electrical properties of Si-, Ge-and Sn-implanted silicon dioxide layers were investigated. It was found, that these layers exhibit strong photoluminescence (PL) around 2.7 eV (Si) and between 3 and 3.2 eV (Ge, Sn) at room temperature (RT), which is accompanied by an UV emission around 4.3 eV. This PL is compared with that of Ar-implanted silicon dioxide and that of Si-and Ge-rich oxide made by rf magnetron sputtering. Based on PL and PL excitation (PLE) spectra we tentatively interpret the blue-violet PL as due to a T 1 → S 0 transition of the neutral oxygen vacancy typical for Si-rich SiO 2 and similar Ge-or Sn-related defects in Ge-and Sn-implanted silicon dioxide. The differences between Si, Ge and Sn will be explained by means of the heavy atom effect. For Geimplanted silicon dioxide layers a strong electroluminescence (EL) well visible with the naked eye and with a power efficiency up to 5 × 10 −4 was achieved. The EL spectrum correlates very well with the PL one. Whereas the EL intensity shows a linear dependence on the injection current over three orders of magnitude, the shape of the EL spectrum remains unchanged. The I − V dependence exhibiting the typical behavior of Fowler-Nordheim tunneling shows an increase of the breakdown voltage and the tunnel current in comparison to the unimplanted material. Finally, the suitability of Ge-implanted silicon dioxide layers for optoelectronic applications is briefly discussed. 78.60.F; 78.55; 61.72.T; 85.30.T; 78.66.J Since the early 60s Si has been the dominating material of microelectronics because of its excellent mechanical, chemical and electrical properties. However, with increasing miniaturization one approaches more and more the physical limits drawn by the material properties of Si. The increase of the line resistance and the corresponding parasitic capacitors with decreasing feature size is opposed to a further miniaturization and an enhancement of the clock rate. The PACS:

The photoluminescence (PL) and electroluminescence (EL) properties of Ge-implanted SiO2 layers thermally grown on a Si substrate were investigated and compared to those of Si-implanted SiO2 films. The PL spectra from Ge-implanted SiO2 were recorded as a function of annealing temperature. It was found that the blue-violet PL from Ge-rich oxide layers reaches a maximum after annealing at 500 °C for 30 min, and is substantially more intense than the PL emission from Si-implanted oxides. The neutral oxygen vacancy is believed to be responsible for the observed luminescence. The EL spectrum from the Ge-implanted oxide after annealing at 1000 °C correlates very well with the PL one, and shows a linear dependence on the injected current. The EL emission was strong enough to be readily seen with the naked eye and the EL efficiency was assessed to be about 5×10−4.

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We present a comprehensive experimental and theoretical study of the optical properties of matrix-isolated molecules of the two perylene derivatives N , NЈ-dimethylperylene-3,4,9,10-dicarboximide ͑MePTCDI͒ and 3,4,9,10-perylenetetracarboxylic dianhydride ͑PTCDA͒. A solid solution of the dyes in an SiO 2 matrix exhibits monomer-like behavior. Transient absorption pump-probe spectroscopy in the range 1.2-2.6 eV has been performed on an ultrafast time scale. The differential transmittance reveals contributions from ground-state bleaching, stimulated emission, and excited-state absorption. Both systems exhibit broad excited-state absorption features below 2.0 eV with a clear peak around 1.8 eV. The spectra can be consistently explained by the results of quantum-chemical calculations. We have applied both the coupled cluster singles and doubles ͑CCSD͒ model and the multireference-determinant single and double configuration-interaction ͑MRD-CI͒ technique on the basis of the intermediate neglect of differential overlap ͑INDO͒ Hamiltonian. The results are insensitive to whether the geometry is optimized for the electronic ground state or first excited state. The experimental polarization anisotropies for the two major transitions are in agreement with the calculated polarizations.

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