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 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 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.