Preferential site substitution in sol-gel derived Eu 3+ doped Lu 2 SiO 5 : a combined study by X-ray absorption and luminescence spectroscopies{
Résumé
Eu 3+ doped Lu 2 SiO 5 (LSO) has been prepared by sol-gel chemistry. X-Ray diffraction showed that only the monoclinic phase corresponding to LSO is observed, even for doped samples. X-Ray absorption measurements were performed at both Lu and Eu L III edges to investigate the substitution of Eu 3+ for Lu 3+ in LSO. Lutetium and europium oxides were used as references for XAFS signal extraction. The validity of XAFS measurements for studying the substitution of Eu 3+ for Lu 3+ at low doping levels (5at.%) was confirmed on a LuBO 3 sample which has a simpler crystalline structure. The XAFS spectrum recorded at the Eu L III edge for Eu 3+ doped LSO demonstrates the effective substitution of Eu 3+ for Lu 3+ and refined inter-atomic distances involving Eu 3+ are consistent with a preferential substitution on the higher coordination site labelled A 2 [LuO 7 ]. Luminescence measurements performed on doped samples show the existence of an impurity phase identified as Lu 2 O 3. Site selective excitation measurements can distinguish between the two crystallographic sites of (Lu,Eu) ions in LSO and the numbering of the Eu 3+ emission lines is in good agreement with the expected C 1 symmetry. De-convolution of the 7 F 0 A 5 D 0 excitation spectrum recorded at room temperature allowed quantification of the populations of the two sites: 37% on A 1 [LuO 6 ] and 63% on A 2 [LuO 7 ]. This result agrees with structural considerations taking into account the difference in the ionic radii of Eu 3+ and Lu 3+ .