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University of the Free State
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In recent years, the study on white light phosphors suitable for ultraviolet (UV) excitation has been attracting more attention for use in white light emitting diodes (LEDs). In white light LEDs, white light can be generated by combination of light of three primary colors (red, green and blue) emitted from different LED chips1 or combination of blue LED with yellow-emitting phosphor materials2,3. It is important to find a phosphor that can be excited under near-ultra-violet and the blue region3. In recent studies it has been established that white light can be generated by doping one or more activator(s) in one matrix. For example, in this study white photoluminescence was generated when Sr2SiO4 co-doped with Tb3+ and Eu3+ was excited at 227 nm using a monochromatized xenon lamp. The calculated Commission Internationale de l’Eclairage (CIE) chromatic coordinates of the generated white light were (x=0.340, y=0.375), which are very close to those of standard white colour (x=0.333, y=0.333). The X-ray diffraction spectra indicated that the Sr2SiO4:Tb3+,Eu3+ phosphor material was successfully prepared at 1000 °C using the solid state method. Scanning electron microscopy images showed agglomeration of particles with irregular shapes. The decay characteristics showed that the phosphor consists of a single exponential decay curve.
(1) Yanmin, Q.; Xinbo, Z.; Xiao, Y.; Yan, C.; Hai, G.; Journal Rare Earths 2009, 27(2), 323
(2) J.K. Park, M.A. Lim, C.H. Kim, H.D. Park Applied Physics Letters 2003, 82(5), 683
(3) Yao, S.; Chen, D.; Central European Journal of Physics 2007, 5(4), 558