ABSTRACT
Connecting electrodes play a crucial role to assist charge injection into the adjacent electroluminescent units in tandem organic light-emitting diodes (OLEDs). In this study, we demonstrate that Mg:Ag alloy is an effective connecting electrode for bottom- and top-emitting tandem OLEDs. Optical cavity design and simulation are also conducted to predict the luminance of tandem OLEDs. It is found that the theoretical luminance of tandem OLEDs is close to but not higher than twofold enhancement over the luminance of a single OLED optimized to the first resonance mode, which is theoretically higher than high-order resonance modes. It is also found that the optical properties of Mg:Ag connecting electrodes, while having relatively small influence on weak microcavity bottom-emitting tandem OLEDs, have large influence on strong microcavity top-emitting tandem OLEDs.
ABSTRACT
White organic light emitting diodes (WOLEDs) is becoming a new platform technology for a range of applications such as flat-panel displays, solid-state lightings etc., and are under intensive research. For general solid-state illumination applications, a WOLED's color rendering index (CRI) and correlated color temperature (CCT) are two crucial parameters. This paper reports that WOLED device structures can be constructed using four stacked emission layers which independently emit lights at blue, green, yellow and red color respectively. The intensity of each emission layer is then engineered by funneling excitons to the targeted emission layer to achieve an ultrahigh 92 CRI at 5000 cd/m(2), and to reduce CCT to below 2500 K.
ABSTRACT
Nonradiative Auger recombination and radiative exciplex emissions at organic-organic heterojunctions are found to be mediated by the nature of the majority charge carrier. The Auger recombination is dominant when the heterojunction is electron rich, the exciplex emission is dominant when the heterojunction is hole rich, and both Auger recombination and exciplex emission are present when the heterojunction is charge balanced.
ABSTRACT
The plasmas generated by dielectric barrier discharge in atmospheric pressure air have wide application prospect in industry. In order to study generation condition and mechanism, the dielectric barrier uniform discharge in atmospheric pressure air has been studied experimentally with a micro-gap discharge device. Results of electrical characteristics indicate that it exist several current pulses with short width in half period of the applied voltage at a low voltage, a large number of micro-discharge filaments are observed. The discharge power increases with increasing peak value of applied voltage, the micro-discharge filaments increase meanwhile. When the peak of applied voltage reaches to 9.2 kV, only a discharge hump with a width of about 5.5 µs appears in a half period of the applied voltage, micro-discharge filaments cannot be discerned. The uniform discharge has been obtained finally as the micro-discharge filaments extend and superimpose randomly. The emission spectrum of dielectric barrier discharge scanning from 330 to 420 nm is collected. It is found that the intensity of 337.1 nm is stronger than that of 391.4 nm. If the intensity of 337.1 nm is considered as the datum reference, the intensity of 391.4 nm shows the magnitude of electron average energy. The molecule internal energy is evaluated by vibration temperature. The electron average energy and molecule internal energy have been investigated by optical emission spectra. It is found that both of them decrease with increasing the applied voltage. Results indicate that it is not easy to form filamentary discharge when the electrical energy is lower. The average electron energy of uniform discharge is lower than that of the filamentary discharge. These results are of great significance to the application of dielectric barrier uniform discharge obtained in air at atmospheric pressure.
ABSTRACT
The characteristics of striations in cylindrical hollow cathode discharge were investigated experimentally. The spectra of striations were measured at a pressure of 20 Pa in a discharge of 1.3 mA, in which the main spectra are the emission spectrum lines of the N2 first positive band (B3pi(g)-->A3pi(u)) and second positive band system (C3pi(u)-->B3pi(g)). The spatial characteristics of vibrational temperature of N2 were calculated based on the theory of double molecular spectrum. It is shown that the emission intensity exhibits a periodic structure with an unequal magnitude, and the spectral intensity of bright striation is higher than that of dark striations. The vibrational temperature of bright striation is of the value of 3500-4400K, moreover the vibrational temperature in the bright regions decreases from the cathode to the anode. In addition, the characteristics of striations at 1.0 mA and 1.5 mA were obtained, and the influence of discharge current on the striations was investigated. It is shown that the vibrational temperature and the distance between two striations increase. Finally the reduced electric field was calculated, which is about 44 approximately 49 m(-1) x Pa(-1), moreover it decreases with the increase in discharge current. The results are very useful for understanding the mechanism of discharge striations and for improving the stability of hollow cathode discharge.
ABSTRACT
The characteristics of striations in cylindrical hollow cathode discharge were investigated experimentally. The emission intensity and spectra of striations were measured, and the spatial characteristics of electron excitation temperature and relative electron density were calculated. It is shown that the emission intensity, the electron excitation temperature and the electron density appear as a periodic structure. The electrons have higher excitation temperature but lower density in the bright regions compared with the dark regions. The electron excitation temperature in the bright regions decreases from the cathode to the anode. It is also shown that the electron excitation temperature increases with increasing current.
ABSTRACT
An improved conical bubble sonoluminescence U-tube was built. Using this setup, the spectra and light pulses of conical bubble luminescence in glycerin were detected. Results show that the spectra are continuum, which are well fitted by blackbody radiation. The cavitational temperature ranging from 2 600 to 3 050 K was calculated from the fitted spectra. The reasons for the existence of blackbody radiation in conical bubble luminescence were discussed both from special and temporal sides. The value of radius of cavitational bubble is about 1.7 cm theoretically, which is greater than that of the bubble acoustically excited. The width of light pulses of cavitational bubble reached 40-60 ms, and this provided enough time for the blackbody radiation. In addition, the light pulses at different wavelength were measured, and results show that the width of light pulses increased with the raise of wavelength of spectra, which proved the mechanism of blackbody radiation. Finally, based on the spectra and light pulses, the intensity of luminescence was calculated to be about 0.18 J.
ABSTRACT
Based on the U-tube, a new type of sonoluminescence apparatus-conical bubble sonoluminescence straight tube apparatus was set up, and the structures and operations were described detailedly. Using the apparatus, the ultrabright cavitation luminescence was obtained in glycol solution. The light pulses of conical bubble sonoluminescence were detected, results show the half width is about 80 micros that is much longer than the results by ultrasound, which should be caused by the fact that the conical bubble can obtain more energy from the flow than the bubbles from the ultrasound. The spectra consist in a broad background ranging from the ultraviolet region to the visible region, on which five clear sequences of Swan bands and three sequences of B 2sigma+ --> X 2sigma+ transition of CN are superimposed. A band assigned to the A 2delta --> X 2II transition of CH was also measured. Specially, the vibrational structures of Swan bands can be resolved. Finally, the achieved molecular vibrational temperature of C2 is estimated to be about (4 200 +/- 200) K.
