Organic semiconductors have been intensively studied over the past decades. The potential of this new class of materials for photonic and electronic device applications is demonstrated by successful fabrication of organic and organic-on-inorganic heterostructures for electroluminescent devices, photodetectors, and microwave diodes. The fabrication technology of organic semiconductor devices for both electronic and photonic applications is discussed. In contrast to spin-on or dipping techniques for fabrication of polymeric Ðlms, organic compounds with low molecular weight are sublimated under ultra high vacuum (UHV) conditions. The organic molecular beam deposition (OMBD) technology employed allows the reproducible growth of complex layer sequences with a deÐned thickness of various organic semiconductors in combination with dielectric Ðlms, di †erent metallizations, and indiumÈtin oxide layers. Growth rates from 1È5 nm min~1 and substrate temperatures from 77 to 350 K are used. Organic-on-inorganic heterostructure diodes based on crystalline thin PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride) Ðlms on IIIÈV semiconductors are investigated with regard to microwave applications with reduced forward voltage and high cut-o † frequencies in the GHz regime. Secondly, efficient organic light emitting diodes with bright emission in the blue [1-AZM-Hex (N,N@-disalicylidene-1,6-hexanediaminate)zinc(II)], green, (tris(8-hydroxyquinoline)-aluminum)], and [Alq 3 red (Eu complexes) spectral region and with low operation voltages are presented. In general an onset voltage of 2.7 V, efficiencies up to 7 lm W~1 and a luminance up to 2 ] 105 cd m~2 (CW, RT) are attained for N,N@diphenyl-quinacridone doped devices. An undoped device can be operated up to 5000 h without any loss Alq 3 in brightness and just a small increase of the driving voltage of about 2 V. Embedding emissive organic thin Ðlms with a narrow spectral characteristic into planar FabryÈPerot microcavities, a light intensity enhancement and a spatial redistribution of the emission is achieved.
An optical fibre sensor for short pulse duration x-ray dosimetry is presented. The sensor is based on luminescence generated in the cladding of a 1 mm core diameter polymer optical fibre which has been doped with a radioluminescent phosphor. On interaction with x-rays, this phosphor emits visible light, part of which is coupled to the fibre core through a combination of surface roughness at the core-cladding interface and through evanescent wave coupling of these guided waves. From here it is transmitted to an optoelectronic photodetector for monitoring. A 15 cm fibre sensor was used for the experiment which was conducted using a pulsed x-ray source normally employed for the preionization of excimer lasers. The results are calibrated against the emission intensity from a scintillating plastic block and a pen dosimeter. The peak output signal of the fibre sensor increases linearly with the dose produced by the x-ray source. There is also a discussion on the long-term stability of such a sensor, the expansion of this sensor into a multi-point device and methods to improve the efficiency of the luminescence coupling from cladding to core for large core polymer fibres included.
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