GLASS CERAMICS FOR SOLID STATE LIGHTING

摘要

Glass ceramic (GC) materials containing a single phase of Ce: YAG micro-crystals were developed from homogeneous glasses in an Y_2O_3-Al_2O_3-SiO_2 system. The glass ceramics show yellow fluorescence due to the Ce~(3+): 5d→4f transition by 460nm excitation. Backward excitation of the GC plate with a blue LED gives white emission, which is binary complementary. From the analyses of the electro-luminescence (EL) measurement data with an integrating, it was revealed that the composite of the GC and a blue LED chip gives high luminous efficiency comparable to that of commercial white LEDs working by the same current power. With increasing GC thickness, the color coordinate (x,y) of the spectra increased owing to the increase of ratio of yellow to blue bands. There exists an optimum thickness for the maximum luminous efficiency, where the GC show maximum yellow fluorescence by absorbing moderate amount of 460nm-light. The variation of color coordinate locus in the CIE chromaticity diagram followed nearly that of the Planckian locus for the black body radiation. The correlated color temperature can also be changed from 8000K to 5000K by increasing GC thickness. With this GC plate, we can avoid the problems of the present packaged white LEDs, i.e., degradation of organic resin, difficulty in packaging of powder phosphors and so on.