Luminescent Y3Al5O12 : Eu3+ (YAG : Eu3+) and Y3Al5O12 : Tb3+ (YAG : Tb3+) 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 Tb3+ and Eu3+ ions were recorded. This study showed, undoubtedly, the spectral features of an Eu3+ emitting centre embedded in a unique site of D2 symmetry. Furthermore, the well-known cross-relaxation phenomenon was observed for Tb3+. Decay times were found to be exponential and shorter than 5 ms for both Eu3+ and Tb3+ activators. Finally, the spectroscopic properties of YAG : Tb3+ powders under vacuum ultra violet excitation were analysed and encouraging results were obtained regarding luminescence efficiency and time constants.
Borate phosphors, with formulations Y0.95Eu0.05BO3 (YBEu), Y0.95Tb0.05BO3 (YBTb), Y0.57Gd0.38Eu0.05BO3 (Y6G4BEu), and Y0.57Gd0.38Tb0.05BO3 (Y6G4BTb) have been synthesized by spray pyrolysis at the maximum temperature of 700 °C, and then annealed at 1200 °C. The yttrium oxide-doped phosphor Y0.95Eu0.05O1.5 (YOEu) was obtained by the same experimental conditions. The UV−VUV excitation spectra of the samples were recorded using synchrotron radiation. The emission intensities of these phosphors have also been investigated as a function of plasma gas pressure in a dedicated experimental setup. The intensities in the emission spectra were integrated, to compare the relative efficiencies of the phosphors. All phosphors were more efficient with increasing gas pressure in the plasma chamber. The emission intensity of YOEu was similar to that of YBEu or Y6G4BEu at low Ne−Xe pressure, but stronger at high pressure. For both lanthanide activators, the mixed borates Y6G4B and the pure YBO3 (YB) have about same luminescence efficiency at low pressure, but the Y6G4B are better matrices than YB at high Ne−Xe pressure. With the introduction of Gd3+ in the borates, the emission intensity is enhanced due to a better spectral overlap with the plasma emission at 173 nm, and also the occurrence of multiple energy transfers between Gd3+ ions before transfer to the emitter Eu3+ or Tb3+. A “color effect” with the variation of pressure in the plasma chamber is observed for the Eu3+-doped phosphors. The orange:red intensity ratio (i.e., 5D0 → 7F0,1 (560−600 nm)/5D0 → 7F2 (600−640 nm)) increases as the gas pressure is raised. This observation is related to the spectral changes occurring in the plasma, and it is corroborated by the observation of selective excitation in the VUV range of Eu3+ at C
i
versus C
1 crystallographic sites.
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