Tricolor devices based on Ba2SiO4:Eu3+ e/ou Tb3+: sol-gel synthesis and eletrophoretic deposition for W-LEDs application

Abstract

White light sources as Light Emitting Diodes (LEDs) are regarded as the next generation of lighting due to the high emission efficiency, longer life time, higher reproducibility of the emitted light, reduction of UV radiation emission and relatively lower temperatures operation compared to fluorescent and incandescent lamps. In LEDs, white light can be obtained by combining red, green and blue phosphors which when excited by a UV or blue light emitting chip generate to the observer a sensation of white light. Phosphors doped with rare earth ions (group of lanthanides included scandium and yttrium), such as Ba2SiO4:Eu3+, Ba2SiO4:Eu2+, Ba2SiO4:Tb3 + and Ba2SiO4:Eu3+, Tb3+ have potential to be applied as components of the emitting layer of white LEDs due to high thermal, electrical and chemical stability. The application of rare earth ions in luminescent materials is usually associated with the ability to replace cations network framing with similar properties in inorganic matrices such as silicates. The synthesis of the phosphors based on silicates, central purpose of this study can be carried out by the sol-gel route, quite a process applied for the production of optically active materials at relatively low temperatures. The sol-gel process is highly versatile, since it allows obtaining a variety of materials such as ceramics, fibers, thin films and glasses. Phosphors prepared from sol-gel route, in turn, can be used in the manufacture of light-emitting films via electrophoretic deposition technique, applicable in the construction of the white LEDs emitting layers, or even screens of televisions or computers. The electrophoretic deposition method is already a standard in literature for the production of white LEDs emitting layer due to the simplicity in obtaining films and enable the deposition of insoluble materials due to the interaction of charges on the surface of an external electric field. Thus the aim of this project is to investigate the structural, morphological and spectroscopic properties of silicates doped with Eu3 +, Eu2+ or Tb3 + and codopaded with Eu3 + and Tb3 + in different percentages, synthesized via sol-gel from barium acetate and TEOS (tetraethoxysilane). After synthesis and modulation of systems properties, it is also desired the production of luminescent films using electrophoretic deposition technique applicable in emitting layer of white LEDs or so in mobile displays, computers or television sets. (AU)