Energy Transfer Processes in NaBiF4 Nanocrystals Co-Doped with Tb3+ and Eu3+ Dispersed in Aqueous Solution

The synthesis of hexagonal NaBiF4 co-doped with Tb3+ and Eu3+(NaBi0.75-xTb0.25EuxF4; with x=0, 5, 10, 20 and 30) was achieved via a facile and fast precipitation route at 35 degrees C. Powder X-ray diffraction (PXRD) and luminescence spectroscopy have been employed to characterize and investigate the materials. The study of luminescence spectroscopy and decay kinetics of the D-5(4) excited state of Tb3+ provides the evidence of a Tb3+-> Eu3+ energy transfer process. Sodium citrate has been adopted as capping agent to promote a homogeneous dispersion of the materials into water and to protect the inorganic host, which is water sensitive, from direct contact with this molecule. The comparison of luminescence properties between bare and citrate-capped samples of NaBiF4 co-doped with Tb3+ and Eu3+ reveals a marked difference in the Tb3+-> Eu3+ energy transfer efficiency, which has been tentatively explained on the basis of a different environment surrounding the lanthanide ions in the two families of compounds.