MOLECULAR-DYNAMICS STUDY OF EU3-SOLUTION - LUMINESCENCE SPECTRUM FROMSIMULATED ENVIRONMENTS( IN AN AQUEOUS)

Because doping ions are mainly surrounded by solvent molecules in the early stages of sol-gel processing, the luminescence of rare-earth ion s in such an environment is known to be very similar to that observed in aqueous solutions. Thus we performed a molecular dynamics simulatio n of the trivalent europium in aqueous solution in order to produce a statistical set of environments and to calculate the spectroscopic fea tures thereof. From radial and angular ordering studies, the hydration number of EU3+ was found to be between eight and nine. The eight-hydr ated configurations are nevertheless predominant and present a specifi c arrangement, according to the geometry of a square antiprism polyhed ron. From the whole set of simulated configurations, we computed the l igand held parameters without considering any a priori symmetry. We th en calculated the energy splitting of each J manifold and the transiti on probabilities from the D-5(0) emitting state. A simulated luminesce nt spectrum was finally obtained and compared with the experimental sp ectrum. In addition to overall good agreement, we were able to analyse the D-5(0) --> F-7(1) transition shape, which revealed a sensitive de pendence on the local structure, and especially on the hydration numbe r.