The use of light-emitting diodes (LEDs) continues to increase dramatically, for example in color computer screens based on flat LED boards which are intended to replace the large and expensive cathode-ray tubes. In the past, it has proved difficult to economically extend the emission spectra of the LEDs into the blue spectral region.The story of the LED goes back to 1907,L'I and in the last 35 years much effort has been invested in the study of inorganic semiconductors e.g. GaN, ZnS, ZnSe and S i c in order to produce an effective blue LED. However, large scale applications have not been practicable due to the problems in fabrication and the rather low luminescence efficiency. Therefore, the use of alternative materials was proposed[21 in order to extend the spectral region into the blue.Organic materials have always been considered for use in electroluminescent devices,[31 but up to now they have not been widely used except for applications in scintillation detectors. Only recently has there been a noticable effort in electroluminescent device fabrication with organic laye r~. [~. ' 1 The observed transfer function between the current input and luminescence output of organic materials is linear, which allows optocouplers without any distortion to be devised. This feature cannot be provided by existing optocoupling devices. A blue light-emitting electroluminescent device, based on low-molecular-weight organic materials with a substantial efficiency was presented recently.I6] A serious disadvantage of devices consisting of organic materials of rather low molecular weight is the tendency of the materials to recrystallize (initiated by the heat produced in the device), which leads to a drastic decrease in quantum efficiency.16] Intensive research activities on the physical properties and synthesis of conjugated polymers[71 have shown these materials to be promising candidates for applications in stable optoelectronic devices. The first encouraging results on LEDs based on semiconducting polymers were reported by Burroughes et al.[*l and confirmed by Braun et al.'91 These devices emitted in the yellowish ( x 600 nm) sprectral range.In the search for new materials for blue LEDs and linear optocouplers, we have investigated the polymer polybphenylene) (PPP, see Fig.

We synthesized the Eu(TTA)3Phen complex and present herein a detailed study of its photophysics. The investigations encompass samples dispersed in poly(vinyl alcohol) and in ethanol in order to explore the versatile applicability of these lanthanide-based materials. Details upon the interaction between Eu, TTA, and the Phen ligands are revealed by Fourier transform infrared and UV-visible absorption, complemented by steady state and temporally resolved emission studies, which provide evidence of an efficient energy transfer from the organic ligands to the central Eu(3+) ion. The material produces efficient emission even under sunlight exposure, a feature pointing toward suitability for luminescent solar concentrators and UV light sensing, which is demonstrated for intensities as low as 200 nW/cm(2). The paper further promotes the complex's capability to be used as luminescence-based temperature sensor demonstrated by the considerable emission intensity changes of ∼4.0% per K in the temperature range of 50-305 K and ∼7% per K in the temeperature range 305-340 K. Finally, increasing the optical excitation causes both spontaneous emission amplification and emission peak narrowing in the Eu(TTA)3Phen complex dispersed in poly(vinyl alcohol) - features indicative of stimulated emission. These findings in conjunction with the fairly large stimulated emission cross-section of 4.29 × 10(-20) cm(2) demonstrate that the Eu(TTA)3Phen complex dispersed in poly(vinyl alcohol) could be a very promising material choice for lanthanide-polymer based laser architectures.

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We report on heteroepitaxial growth of nearly monodisperse PbS nanocrystals onto the surface of TiO 2 nanoparticles via colloidal hot-injection routes. Fabricated PbS/TiO 2 nanocomposites can be dispersed in nonpolar solvents, which enables an easy solution processing of these materials into mesoporous films for use as light-absorbing layers in nanocrystal-sensitized solar cells. High-temperature deposition of the sensitizer material allows controlling both the size and the number of PbS domains grown onto TiO 2 nanoparticles, whereby providing synthetic means for tuning the absorbance spectrum of PbS/TiO 2 nanocomposites and simultaneously enhancing their photocatalytic response in the visible and near-infrared. Compared with conventional ionic bath deposition of PbS semiconductors onto TiO 2 , the reported method results in an improved nanocrystal quality and narrower distribution of PbS sizes; meanwhile, the use of hot-temperature deposition of PbS (T ) 180 °C) promotes the formation of near-epitaxial relationships between PbS and TiO 2 domains, leading to fewer interfacial defects. The photovoltaic response of pyridine-treated PbS/TiO 2 nanocomposites was investigated using a two-electrode cell filled with polysulfide electrolyte. The measured photocurrent compared favorably to that of PbS/TiO 2 electrodes fabricated via chemical bath deposition.

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