[en] Thin films of a-C:N and a-SiC:N deposited by diode r.f. sputtering and magnetron sputtering, respectively, were used as electron injection layers in organic light emitting diodes. The devices consist of two different heterojunction structures: the first one, indium tin oxide (ITO)/hole transport layer (HTL)/electron transport layer (ETL)/a-C:N/Al and the other one formed by ITO/HTL/ETL/a-SiC:N/Al. The HTL was obtained using a thin film of 1-(3-methylphenyl)-1,2,3,4 tetrahydroquinoline-6-carboxyaldehyde-1,1'-diphenylhydrazone (MTCD), while the tris(8-hydroxyquinoline aluminum) (Alq₃) is used as ETL. For all produced devices a significant increase in the current compared to the conventional ITO/MTCD/Alq₃/Al structure was observed. Light emission was detected in both ITO/MTCD/Alq₃/a-C:N/Al and ITO/MTCD/Alq₃/a-SiC:N/Al structures. The results are interpreted in terms of a highly efficient electron injection from the carbon nitride layer into the electron transporting one. The electroluminescent spectra of the devices are also reported and discussed

[en] In this work, the growth and the characterization of new orange emitting triple-layer electroluminescent organic devices using vacuum deposited trivalent samarium complex [Sm(TTA)₃(TPPO)₂] as emission layer is described. The electroluminescence (EL) spectra of the devices show narrow bands arising from the ⁵G_5/2→6H_J transitions (J=5/2, 7/2 and 9/2) of the Sm³⁺ ion with the hypersensitive ⁵G_5/2→6H_J transitions as the prominent group. The hole transporting layer (HTL) was obtained using a thin film of 1-(3-methylphenyl)-1,2,3,4 tetrahydroquinoline-6-carboxyaldehyde-1,1'-diphenylhydrazone (MTCD), while the tris(8-hydroxyquinoline aluminum) (Alq₃) is used as electron transport layer (ETL). Moreover, in order to use the Sm complex, two different kinds of OLEDs were prepared: the first one with a typical three layers architecture, MTCD/[Sm(TTA)₃(TPPO)₂]/Alq₃, while the second one was a bi-layer device with an MTCD/[Sm(TTA)₃(TPPO)₂] design without the Alq₃ ETL layer. In the last case, the EL emission was also observed, which indicates that the [Sm(TTA)₃(TPPO)₂] complex may be used as an electron transporting layer also

[en] Most of the Organic Light-Emitting Diodes (OLEDs) have a multilayered structure composed of functional organic layers sandwiched between two electrodes. Thin films of small molecules are generally deposited by thermal evaporation onto glass or other rigid or flexible substrates. The interface state between two organic layers in OLED device depends on the surface morphology of the layers and affects deeply the OLED performance. The morphology of organic thin films depends mostly on substrate temperature and deposition rate. Generally, the control of the substrate temperature allows improving the quality of the deposited films. For organic compounds substrate temperature cannot be increased too much due to their poor thermal stability. However, studies in inorganic thin films indicate that it is possible to modify the morphology of a film by using substrate vibration without increasing the substrate temperature. In this work, the effect of the resonance vibration of glass and silicon substrates during thermal deposition in high vacuum environment of tris(8-quinolinolate)aluminum(III) (Alq₃) and N,N′-Bis(naphthalene-2-yl)-N,N′-bis(phenyl)-benzidine (β-NPB) organic thin films with different deposition rates was investigated. The vibration used was in the range of hundreds of Hz and the substrates were kept at room temperature during the process. The nucleation and subsequent growth of the organic films on the substrates have been studied by atomic force microscopy technique. For Alq₃ and β-NPB films grown with 0.1 nm/s as deposition rate and using a frequency of 100 Hz with oscillation amplitude of some micrometers, the results indicate a reduction of cluster density and a roughness decreasing. Moreover, OLEDs fabricated with organic films deposited under these conditions improved their power efficiency, driven at 4 mA/cm², passing from 0.11 lm/W to 0.24 lm/W with an increase in their luminance of about 352 cd/m² corresponding to an increase of about 250% in the luminance with respect to the same OLEDs fabricated in the same way and with the same conditions without substrate vibration.

[en] The structure of the zero-phonon line at 1.53 μ-m in e^--irradiated Tl⁺-doped KCl has been investigated as a function of temperature. The particular color center which originates the discrete phonon structure has not been identified, but it is coupled to a localized mode ℎω = 3.9 meV and possesses a rather small Huang-Rhys factor, S = 1.7. Moreover the narrow absorption structure and the band underneath are essentially stable over a period of almost one year. (Author)

[en] Several color centers, which are of some interest for pulsed laser emission, can be produced in LiF crystals. Among these centers, which are stable at room temperature under optical pumping, the F₃⁺ center, after absorbing at ∼450 nm, displays an emission at ∼535 nm, which has unusual dependences on time, excitation power, and temperature. A triplet state in the optical cycle can explain its peculiar properties, and in this work an accurate study of the absorption and emission has been accomplished as a function of temperature. These measurements have shown the existence of multiphonon processes in the energy transfer transitions to and from the triplet state. Moreover better conditions for laser action have been found at temperatures lower than RT, where there is the possibility of having a c.w. laser emission

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[en] In this letter, the development of a simple method, based on high-energy light-ion beam irradiation, to create active waveguides in alkali halide materials is reported. A 1.1 MeV He⁺ beam at normal incidence was used to irradiate lithium fluoride crystals, with different ion doses varying from 1x10¹² up to 6x10¹⁵ cm^-2, producing thin colored strips. All strips showed several guided modes, confirming the effectiveness of this technique to create the conditions to allow guided propagation. Values of 1.5 dB/cm were found for the propagation losses

[en] Sol–gel method has shown several advantages for oxide synthesis, such as lower cost production, coating large areas, lower processing temperatures and ease insertion of doping materials. Therefore, it is attractive for production of intermediate and electrode modifying layers in organic optoelectronic devices. Herein, spin-coated aluminum-doped titanium dioxide (AlTiO_2) thin films were produced by sol–gel method onto glass and fluorine-doped tin oxide (FTO) substrates, using different Al-dopant concentrations and post-done annealing temperatures. Electrical measurements were performed in order to investigate the improvement of the TiO_2 resistivity. Additionally, structural, compositional, morphological, optical and electrical properties of the optimal AlTiO_2 modifying layers onto FTO substrates were probed by different techniques, and compared with those obtained from the undoped thin films produced under similar conditions. Organic photovoltaic devices (OPVs) with the structure FTO/AlTiO_2(30 nm)/C_6_0(50 nm)/CuPc(50 nm)/Al with an Al concentration of 0.03 M in AlTiO_2 layer were produced. The insertion of AlTiO_2 thin films improved the short-circuit current density (J_s_c) as well as the open circuit voltage (V_o_c) in comparison with non-modified electrode FTO based devices. This behavior is discussed in terms of induced interface phenomena as dipole formation induced by Al. - Highlights: • Easy and cheap solution-process for AlTiO_2 modification of FTO electrode for OPVs • Electrical, structural and optical characterization of TiO_2 layers with Al-dopant • Improvement of Voc and Jsc of inverted OPVs with AlTiO_2 modified electrode