We demonstrate markedly improved electroluminescence (EL) intensity and reduced external quantum efficiency (EQE) roll-off of a device which presents two emitting layers of fac-tris-(2-phenylpyridine) iridium [Ir(ppy) 3 ] in 4,4-bis(9-carbazolyl)-2,2-biphenyl (CBP) and 1,3-bis[2-(2,2-bipyridine-6-yl)-1,3,4-oxadiazo-5-yl]benzene (Bpy-OXD); 4,7-diphenyl-1,10-phenanthroline/Bpy-OXD layers were used as hole blocking and electron transport layers. The device exhibits a maximum EQE of 15.5% (corresponding to an efficiency of 56.8 cd A −1) at a luminance of 600 cd m −2 , which is twice the value (8.2%) of the reference diode using Ir(ppy) 3 doped CBP as a single emitting layer; the device still maintained a 6.5% efficiency at a luminance of 70 450 cd m −2. The mechanism of this marked improvement in EL intensity and decrease in the EQE roll-off was also explored in detail.

We report a double stage linearly polarized ytterbium-doped double clad fiber (YDCF) amplifier working at 1063.9 nm, which generates a diffraction-limited output with an average power of 102 W at a repetition rate of 100 kHz, a pulse duration of 14.9 ns, a peak power of 68 kW, a 3 dB spectral width of about 0.47 nm and a polarization extinction ratio (PER) of about 13 dB. The seed is modulated to work at a suitable Gaussian shape to restrain the pulse distortion in the fiber amplifier. To the best of our knowledge, this result represents the highest peak power with narrow line-width and excellent beam quality in linearly polarized YDCF.