YAG:Ce nanoparticle based converter layer for white LEDs

Our work is devoted to the development of YAG:Ce³⁺ nanoparticle based films for white LEDs. Very stable suspensions of YAG:Ce nanoparticles are synthesized by a glycothermal method at relatively low temperature (300°C). Protected annealing in a silica matrix allows the further treatment of these nanoparticles at high temperature without any aggregation or growth while still allowing a significant improvement of their quantum yield and photostability. The obtained colloidal nanoparticles are finally incorporated into different matrices to be used as converter layer for white LEDs. First, the incorporation in silicone caps confirms that the annealed particles are much more efficient than the asmade ones and leads to white light generation. YAG:Ce nanoparticles are also dispersed into a sol-gel matrix of TiO₂. Thanks to the relative matching of refractive indexes between TiO₂ and YAG, and to the sub-wavelength particles size, YAG/TiO₂ films do not scatter, as opposed to the same film containing the commonly used micron size phosphor. Nevertheless, they are not absorbent enough. Thus, YAG:Ce suspensions are then spray-coated to obtain thicker and non diluted films. These films scatter photons but this can be solved by filling their porosity with a high refractive index matrix. A yellow component is detected when deposited onto a blue LED, meaning that they absorb much more than the YAG:Ce/TiO₂ system. When used as light converters for white LEDs, these spray-coated films could offer the opportunity to diminish the backscattered light absorption losses.