Thermally activated delayed fluorescence (TADF) has attracted much attention for realization of highly-efficient and low-cost organic light emitting diodes (OLEDs). OLEDs based on 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), which is one of highly-efficient TADF emitters, have been demonstrated to exhibit external quantum efficiency more than 19%. To study the decay rates from excited states of 4CzIPN, the temperature dependence of photoluminescence quantum efficiency (PLQE) has been measured in the weak photoexcitation limit in 4CzIPN-doped 1,3-bis(9-carbazolyl)benzene thin films. Characteristic features of the temperature dependence of PLQE in the weak photoexcitation limit are found, and examined by using rate equations of singlet and triplet densities.
Leuco dyes, well-known multi-functional material, can exhibit excellent thermochromic properties by combining with developer molecule which is organic compound having a hydroxyl group and long alkyl chain. Our purpose of this research is to fabricate multifunctional material enabling control of both emission and coloration by combining leuco dye-developer system with emission materials. In this study, we investigated novel thermo-responsive dual-mode displaying media showing both reflective and emissive modes in red-green-blue (RGB) three primary colors. We employed the two kinds of leuco dye derivatives into the polymeric film as thermochromic material in order to improve the switching contrast of the emissive mode. As a result, we successfully demonstrated the control of coloration and emission in RGB colors with large contrast by thermal treatments.
Transfer performance of xerographic process is represented in the point of transfer latitude by the electric field simulation. The latitude is defined by the bias voltage window between the minimum voltage to transfer toner images and the maximum voltage to prevent defects on the image caused by discharge inside the transfer nip. In this point of view, numerical analysis on the second transfer process in an intermediate transfer system is conducted. The results of the electric field simulation indicate that the latitude can be maximized by optimizing the thickness and specific resistance of the layer inside the bias transfer roller (BTR) and that difference of dependence of maximum transfer bias voltage and minimum transfer bias voltage to the system resistance generates the transfer latitude. The procedure is useful for product design process to develop reliable product with less resources.
Toner scatter is one of the major image degradations at 2nd transfer unit in xerographic process. To clarify the mechanism of the phenomenon, one-dimensional numerical simulations on the electric field including effects of discharge were executed to investigate electric forces on toner particles. In the simulation, the electric field intensity in the process direction on a printed area was defined as a characteristic value for evaluating the degree of toner scatter. As a result, it was found that the electric field which raises the toner scatter was generated when the charge on media in a contact area is not sufficient. Factorial effects calculated by the simulation model were in good agreement with the experimental ones.
To obtain the desired images from inkjet printers, it is important to control the coalescing and wetting behaviors of the ink droplets. However, predicting these behaviors quantitatively through an experimental approach is difficult because of the speed and the minuteness of such phenomenon. Therefore, the establishment of a simulation technology to predict these behaviors is in demand. In this study, an MPS simulation method was developed based on a particle method that considered the effect of surface tension acting on the liquid-liquid and liquid-solid interfaces. Quantitative prediction of the coalescing and wetting behaviors was made possible using this technology.
A dual-mode display device which can operate in both emissive and reflective modes, having advantages of both modes, is considerable promise as a next generation display. In this review, electrochemical switching systems, which enable simultaneous control of both emission and coloration, are reviewed in order to create the novel displaying materials. A luminescent europium(III) [Eu(III)] complexes, one of the important lanthanide (III) complexes, and electrochromic molecules of viologen derivatives were combined for appearance of the multi-functionality. The Eu(III) complex emission was controlled by the electrochromism of the viologen derivatives via an intermolecular energy transfer mechanism. When viologen derivatives were in a colorless state, a strong red emission was observed from the Eu(III) complex. On the other hand, the electrochemically colored viologen derivatives effectively quenched the red emission of the Eu(III) complex. However, these systems lacked quick response and high reversibility of the fluorescence modulations. Some of the researches for improving these disadvantage of primary study are described. Furthermore, numerical representations and multi-color representations with emissive and reflective modes were also achieved.