LBL luminescent thin films of rare earth doped Ba2SiO4 obtained via sol-gel for white LED application

Abstract

White light sources as light emitting diodes (LEDs) are regarded as next-generation lighting because of 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 is obtained by combining red, green, and yellow phosphors in addition to a blue emitting layer and when simultaneously emit light the observer has the perception of white light. Phosphors doped with rare earth ions (group that includes lanthanides plus scandium and yttrium), such as Ba2SiO4: Eu3 +, Ba2SiO4: Tb3 + and Ba2SiO4: Eu3 +, Tb3 + have potential to be applied as components of the emitter layer of white LEDs, and displays screens, cell imaging, solid state lasers, or chemical sensors. The application of rare earth ions in luminescent materials is generally associated with the ability to replace cations with similar properties in inorganic matrices as silicates. Silicates are groups of the basic inorganic compounds of silicon and oxygen that may be classified according to how the SiO44- tetrahedra are bound together, forming a lattice that can be deformed due to the presence of a dopant ion such as Eu3 + or Tb3 +. The simplest silicates, orthosilicates, are built by isolated tetrahedral units SiO44- and electrical neutrality is provided by cations regularly spaced along the chain. The synthesis of a silicate-based phosphor, such as the materials proposed in this work, can be carried out by the sol-gel route, a process well applied for the synthesis of materials with optical properties at relatively low temperatures. The sol-gel process is quite important in several research areas, as it allows obtaining a series of materials such as ceramics, fibers, thin films and glasses. The proposed materials obtained by sol-gel pathway can be used in the manufacture of thin film technique via layer-by-layer, creating a system which can be applied in the layer emitting white LEDs, as well as screens for televisions or computers. Thus, the purpose of this work is to investigate the structural, morphological and spectroscopic doped silicate with Eu3 + or Tb3 + and co-doped with Eu3 + and Tb3 + in different percentages, synthesized via sol-gel from barium acetate and TEOS (tetraethoxysilane). After synthesis and modulation of system properties is also intended the luminescent manufacturing of nanostructured thin films using the layer-by-layer technique and the cationic polymer PAH (polyallylamine Hydrochloride) aiming emitting layer application such as white LEDs or else in displays mobile phones, computers or television sets.