Efficient red organic light-emitting device consisted of a compound fluorescent-phosphor-sensitized emission layer was fabricated. A novel red fluorescent dye, 3-(dicyanomethylene)-5,5-dimethyl-1-(4-dimethylamino-styryl) cyclohexene (DCDDC), and a green phosphorescent dye, fac tris(2-phenylpyridine) iridium [Ir(ppy)3] were codoped into a host material 4,4'-N,N'-dicarbazolebiphe-nyl (CBP). By adjusting the component ratio of doping system, a series of devices with different concentration proportion of Ir(ppy)3:DCDDC were constructed. The results demonstrated that the device with 0.2 wt% DCDDC had a maximum power effi-ciency (ηp) of 2.12 lm/W at a current density of 0.1 mA/cm2, which was about 38% higher than that of conventional fluorescent device. When at a current density of 4 mA/cm2 (100 cd/m2) and 52 mA/cm2 (1000 cd/m2), the ηp percentage was about 160% and 143% higher than that of conventional device, respectively. A stable red light emission at a peak of 615 nm with Commissions Internationale de l'Eclairage coordinates near the region of (0.56, 0.42) in a wide bias range was also obtained. The improved performances were attributed to the efficient multiple-stage energy transfer from the host to the guest and the suppression of loss mechanism.
Nanocrystalline VO2 thin films were deposited onto glass slides by direct current magnetron sputtering and postoxidation. These films undergo semiconductor-metal transition at 70 ℃, accompanied by a resistance drop of two magnitude orders. The crystal structures and surface morphologies of the VO2 films were characterized by x-ray diffraction （XRD） and atomic force microscope （AFM）, respectively. Results reveal that the average grain size of VO2 nanograins measured by XRD is smaller than those measured by AFM. In addition, Raman characterization indicates that stoichiometric VO2 and oxygen-rich VO2 phases coexist in the films, which is supported by x-ray photoelectron spectroscopy （XPS） results. Finally, the optical properties of the VO2 films in UV-visible range were also evaluated. The optical band gap corresponding to 2p-3d inter-band transition was deduced according to the transmission and reflection spectra. And the deduced value, Eopt2p-3d ： 1.81 eV, is in good agreement with that previously obtained by theoretical calculation.
