Site selectively excited luminescence and energy transfer of X-1-Y2SiO5 : Eu at nanometric scale

Two different types of structure called X-1 and X-2 are existing in Y2SiO5 at normal conditions. In X-1 type, Y3+ ions occupy two sites where they are surrounded respectively by nine and seven oxygen ions, while in X-2 struct ure, only six and seven oxygen ions are involved. Nanometric scale X-1-Y2Si O5 crystals were prepared by sol-gel method with particle size around 50 nm . Site selective excitation at low temperature has shown four different lum inescent centers. Two of them belong to Eu3+ embedded in X-1-Y2SiO5, the ot her two are attributed to Y2O3:Eu phase and to a particular site on the sur face. The occurrence of the latter site may be related to the nanometric si ze of the sample. A pronounced excitation energy transfer from site 2 to si te 1 was also observed on excitation spectra. The energy transfer rate incr eases rapidly with increasing Eu3+ concentration and for x=0.7 in Y2-xSiO5: Eu-x, no fluorescence takes place in site 2 at 15 K. The lifetimes of the D -5(0) levels of Eu3+ in the two sites were measured as a function of Eu3+ c oncentration. The results have shown that the lifetime of the D-5(0) level of Eu3+ in site 2 decreases with increasing Eu3+ concentration. The energy transfer rate dependence upon temperature was studied in detail and compare d to a theoretical simulation. (C) 1999 American Institute of Physics. [S00 21-8979(99)06319-7].