Luminescence properties of octahedrally coordinate Eu2+ ions
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In this dissertation, we investigated Eu2+ ion in CsCaF3 and Rb2MP2O7 with M=Ca,Sr. The emission spectra of Eu2+ ion doped in CsCaF3 shows a very unique behavior. Depending on temperature, the peak of the emission shifts from 628 nm at 6 K to 520 nm at 300 K. This shift has been attributed to the presence of the two Eu2+ sites or alternatively to anomalous emission i.e, emission from an impurity bound exciton. From relevant optical data, the centroid shift, red shift, Stokes shift and the lowest excited-energy location are estimated. The luminescence parameters of Eu2+ in CsCaF3 are discussed and arguments are presented to associate the luminescence with the anomalous emission transition. We also report on the excitation and emission spectra of the octahedrally coordinated Eu2+ ions in Rb2MP2O7 with M=Ca, Sr. Again, the centroid shift, red shift and Stokes shift and the energy of the lowest-excited state are estimated from optical data. The Eu2+ emission in these materials is characterized by a large Stokes shift, which, for phosphates, results in the lowest reported emission bands peak at 645 nm and 590 nm for Rb2CaP2O7 and Rb2SrP2O7, respectively. At this point, Eu2+ emission in these materials can be ascribed to a normal, although extreme case, of the intra-ion 4f65d1 ! 4f7[8S7=2] transition.