Optical Properties of Microcavity Structures using the Organic Light Emitting Materials
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Optical Properties of Microcavity Structures using the Organic Light Emitting Materials Boo Young Jung, Nam Young Kim, Chang Hee Lee, Chang Kwon Hwangbo, and Chang Seoul1 Department of Physics, Inha University, Inchon 402-751, Republic of Korea 1Department of Textile Engineering, Inha University, Inchon 402-751, Republic of Korea ABSTRACT We investigated the optical properties of Fabry-Perot microcavity with a tris(8hydroxyquinoline)aluminum (Alq3) organic film by measuring the photoluminescence (PL) and transmittance. An Alq3 layer as an active layer was sandwiched between two mirrors, which were metal or (TiO2|SiO2) dielectric multilayer reflectors. An Alq3 layer on glass, [air|Alq3|glass], showed a PL peak around 513 nm and its full width half maximum (FWHM) was about 80 nm. Three types of microcavity, such as Type A [air|metal|Alq3|metal|glass], Type B [air|dielectric|Alq3|dielectric|glass], and Type C [air|metal|Alq3|dielectric|glass], were fabricated. The result shows that the FWHMs of three Fabry-Perot microcavities were reduced to 15~27.5, 7~10.5 and 16~16.6 nm, respectively, and the microcavity structure is expected to improve the efficiency and tunability of emission spectrum in display. INTRODUCTION Tang and Van Slyke [1] introduced the organic light emitting devices (OLED) using Alq3 as an emitting material in 1987. The organic light emitting material such as Alq3 has been expected to play a significant role in future display technology, since it has the high fluorescence quantum efficiency in the visible spectrum and properties of semiconductor. Compared with the inorganic LED, the organic LED is to be fabricated at a low cost as well as in a flexible way. As the lifetime of OLED is improved, it is recently used in the car radio display. A microcavity structure [2-5] has been expected to show the narrow spectral emission, Q3.5.1
the improvement of emission efficiency, the tunable emission spectrum, the fabrication of organic semiconductor laser [6], the application of optical switching and optical sensor, and the source of optical communication. The cavity is formed between top and bottom mirrors that are (TiO2|SiO2) distributed Bragg reflectors or metal. In this study, we used Alq3, a light emitting material in green, as an active layer and simulated the phase change on reflection at the interface between mirror and Alq3 film. Also we showed two ways to control a resonant wavelength (RW) of microcavity. First, it is to adjust the cavity length as a common method. Second, it is to control the phase change on reflection [5]. EXPERIMENTAL In order to obtain the maximum quantum efficiency, it is important that the mirrors have the minimum reflectance at an excitation wavelength and the wavelength of the maximum PL peak intensity is coincident with the RW. We designed our specimens to be in the optimum condition and they were three types: Type A is [air|Ag|Alq3|Ag|glass], Type B [air|(LH)6|Alq3|(LH)6|glass], and Type C [air|Ag|Alq3|(LH) n|glass]. In this paper L stands for the quarter wave
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