# ENERGY TRANSFER PROCESS BETWEEN $Ce^{3+}$ AND $Tb^{3+}$ IN LaOCl HOST

• Kim, Taesam (Korea Institute of Geology, Mining and Materials) ;
• Sung, Hakje (Korea Institute of Geology, Mining and Materials) ;
• Kim, Kunhan (Korea Institute of Geology, Mining and Materials) ;
• Ha, Younggu (Department of Chemistry, Seoul National University) ;
• Chang, Joowhan (Department of Chemistry, Hannam University) ;
• Song, Sunho (Department of Chemistry, Hannam University)
Energy transfer process between $Tb^{3+}$ and $Ce^{3+}$ has been studied in LaOCl host. The energy absorbed by $Ce^{3+}$ transfers to $Tb^{3+}$ which has levels emitting strong fluorescence. The probability of energy transfer depends strongly on the concentration or the distance of activator ions. While the energy transferred on $Tb^{3+}$ emits from $^5D_3$ level at low concentration of $Ce^{3+}$, the energy goes back to $Ce^{3+}$(Back Transfer) and then emits from low levels of $Ce^{3+}$ and $Tb^{3+}$ at the high concentration. The Back Transfer process has been identified by the experiment with varying the concentration of the activator, $Ce^{3+}$. The relaxation is more effective if $Ce^{3+}$ intermediates than if not.