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).
A protected annealing in a silica matrix allows further treatment of these nanoparticles at high temperature without any
aggregation and growth and with 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 epoxy caps confirms that the annealed particles are much more efficient than the as-made 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/TiO2films are not scattering, contrary 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 are a bit scattering 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.
We report here a method to enhance light extraction from the top face of a TiO2 waveguide doped with a molecular
emitter. Sol-gel TiO2 surface is patterned by a 2D photonic crystal with a 400-nm period and a 40-nm depth, as verified
by Scanning Electron Microscopy and Atomic Force Microscopy. We evidence that light emitted in the TiO2 layer is
efficiently extracted by the surface patterning and quantify the extraction enhancement by measuring the emission
spectra as a function of the emission angle. We measured an enhancement factor of 3 within 50° off normal.