Sol–gel based YAG : Tb3+or Eu3+phosphors for application in lighting sources

Luminescent Y 3 Al 5 O 12 : Eu 3+ (YAG : Eu 3+ ) and Y 3 Al 5 O 12 : Tb 3+ (YAG : Tb 3+ ) powders with nanometre and micrometre-sized particles and films have been successfully synthesized by sol–gel route from alkoxide precursors. Advanced YAG coatings were achieved by spray and dip-coating methods, giving rise to different structural and optical properties. High temperature x-ray diffraction, x-ray powder diffraction, scanning electron microscopy and atomic force microscopy were used to investigate the materials structure and morphology. Pure polycrystalline YAG powder was obtained from 900°C. Laser induced luminescence spectra as well as luminescence decays of Tb 3+ and Eu 3+ ions were recorded. This study showed, undoubtedly, the spectral features of an Eu 3+ emitting centre embedded in a unique site of D 2 symmetry. Furthermore, the well-known cross-relaxation phenomenon was observed for Tb 3+ . Decay times were found to be exponential and shorter than 5 ms for both Eu 3+ and Tb 3+ activators. Finally, the spectroscopic properties of YAG : Tb 3+ powders under vacuum ultra violet excitation were analysed and encouraging results were obtained regarding luminescence efficiency and time constants.