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

Gd3Ga5O12 and Y3Al5O12 nanocrystalline powders codoped with Yb3+ and Tb3+ or Eu3+ have been prepared using the sol-gel Pechini method. Nanocrystals obtained by this technique exhibit a cubic phase with the Ia3 (d) over bar 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 oil these samples. Green/blue or red visible upconversion luminescence from Tb3+ D-5(3), D-5(4) -> F-7(J), or Eu3+ D-5(0) -> F-7(J) transitions, respectively, has been observed upon Yb3+ F-2(7/2) -> F-2(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.