We report on an efficient wide-band-gap host material for blue electrophosphorescence devices, namely, 1,2-trans-di-9-carbazolylcyclobutane (DCz). Photophysical studies show that lower-energy excimer formation between the carbazole units can be efficiently suppressed in a DCz film, thus maintaining its high triplet-state energy and inducing an exothermic energy transfer from DCz to iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate (FIrpic). Electrophosphorescent devices comprising a FIrpic:DCz emitting layer exhibit a superior performance with a maximum external quantum efficiency of 9.8%, a maximum luminance efficiency of 21.5cd∕A, and a maximum power efficiency of 15.0lm∕W at 0.01mA∕cm2.
One of the important factors for high efficiency phosphorescent organic light-emitting devices is to confine triplet excitons within the emitting layer. We synthesized and characterized a new hole blocking material containing silane and triazine moieties, 2,4-diphenyl-6-(49-triphenylsilanylbiphenyl-4-yl)-1,3,5-triazine (DTBT). Electrophosphorescent devices fabricated using the material as the hole-blocking layer and N,N9-dicarbazolyl-4,49-biphenyl (CBP) doped with fac-tris(2-phenylpyridine)iridium [Ir(ppy) 3 ] as the emitting layer showed a maximum external quantum efficiency (g ext ) of 17.5% with a maximum power efficiency (g p ) of 47.8 lm W
21, which are much higher than those of devices using bathcuproine (BCP) (g ext = 14.5%, g p = 40.0 lm W 21 ) and 4-biphenyloxolate aluminium(III) bis(2-methyl-8-quinolinato)-4-phenylphenolate (BAlq) (g ext = 8.1%, g p = 14.2 lm W
21) as hole-blocking layers.
Discharge with an external magnetic field is promising for various applications of low-temperature plasmas from electric propulsion to semiconductor processes owing to high plasma density. It is essential to understand plasma transport across the magnetic field because plasma confinement under the field is based on strong magnetization of light electrons, maintaining quasi-neutrality through the inertial response of unmagnetized ions. In such a partially magnetized plasma, different degrees of magnetization between electrons and ions can create instability and make the confinement and transport mechanisms more complex. Theoretical studies have suggested a link between the instability of various frequency ranges and plasma confinement, whereas experimental work has not been done so far. Here, we experimentally study the magnetic confinement properties of a partially magnetized plasma considering instability. The plasma properties show non-uniform characteristics as the magnetic field increases, indicating enhanced magnetic confinement. However, the strengthened electric field at the edge of the plasma column gives rise to the Simon–Hoh instability, limiting the plasma confinement. The variation of the edge-to-center plasma density ratio (h-factor) with the magnetic field clearly reveals the transition of the transport regime through triggering of the instability. Eventually, the h-factor reaches an asymptotic value, indicating saturation of magnetic confinement.
Internal reconnection events (IREs), one of the relaxation events driven by internal magnetohydrodynamic (MHD) instabilities in fusion plasmas, are accompanied by a strongly MHD-correlated blob at the edge in the VEST spherical tokamak. The MHD-correlated blob plays a significant role in the onset and the strength of IREs. Various techniques analyzing visible camera images show correlated waveforms between blobs and magnetic fluctuations, and they produce visualized images of corotating structures of the MHD modes and the MHD-correlated blobs. In the images, a phase drag in the rotations of the two structures initially appears and vanishes on the verge of IREs. IREs maintaining the phase drag, however, leads to a less violent impact in terms of current decrease and magnetic field bursting. In addition, the MHD-correlated blobs are followed by the increasing degree of nonlinear interactions between the internal MHD mode and high-frequency broadband fluctuations (> 60 kHz) at the edge. These results suggest that boundary plasmas can impact internally driven relaxation events via MHD-correlated edge phenomena.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.