Preferential site substitution in sol-gel derived Eu3+ doped Lu2SiO5: a combined study by X-ray absorption and luminescence spectroscopies

摘要

Eu3+ doped Lu2SiO5 (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 Eu3+ for Lu3+ in LSO. Lutetium and europium oxides were used as references for XAFS signal extraction. The validity of XAFS measurements for studying the substitution of Eu3+ for Lu3+ at low doping levels (5at.%) was confirmed on a LuBO3 sample which has a simpler crystalline structure. The XAFS spectrum recorded at the Eu L-III edge for Eu3+ doped LSO demonstrates the effective substitution of Eu3+ for Lu3+ and refined inter-atomic distances involving Eu3+ are consistent with a preferential substitution on the higher coordination site labelled A(2) [LuO7]. Luminescence measurements performed on doped samples show the existence of an impurity phase identified as Lu2O3. Site selective excitation measurements can distinguish between the two crystallographic sites of (Lu,Eu) ions in LSO and the numbering of the Eu3+ emission lines is in good agreement with the expected C-1 symmetry. De-convolution of the F-7(0) -> D-5(0) excitation spectrum recorded at room temperature allowed quantification of the populations of the two sites: 37% on A(1) [LuO6] and 63% on A(2) [LuO7]. This result agrees with structural considerations taking into account the difference in the ionic radii of Eu3+ and Lu3+.