Upconversion Luminescence in Nanocrystals of Gd₃Ga₅O₁₂ and Y₃Al₅O₁₂ Doped with Tb³⁺−Yb³⁺ and Eu³⁺−Yb³⁺

Gd 3 Ga 5 O 12 and Y 3 Al 5 O 12 nanocrystalline powders codoped with Yb 3+ and Tb 3+ or Eu 3+ have been prepared using the sol−gel Pechini method. Nanocrystals obtained by this technique exhibit a cubic phase with the I a 3 d̅ space group. Particles show a broad distribution of sizes and shapes, ranging from elongated to quasi-spherical particles of tens of nanometers. Optical properties such as photoluminescence and excitation spectra or lifetime measurements have been studied on these samples. Green/blue or red visible upconversion luminescence from Tb 3+ 5 D 3, 5 D 4 → 7 F J, or Eu 3+ 5 D 0 → 7 F J transitions, respectively, has been observed upon Yb 3+ 2 F 7/2 → 2 F 5/2 excitation at 975 nm. A detailed investigation on the spectroscopy and excited state dynamics of these systems is extremely important in order to understand the upconversion processes.