Crystal structure of ABPO5 and optical study of Pr3+ embedded in these compounds

The crystal structure of borophosphates ABPO(5) (A = alkaline earth or Pb) Was resolved on a polycrystalline sample using the Rietveld method. The x-ray diffraction patterns data show that ABPO(5) crystallize in a centrosymmetric space group P3(1)21 and their structure is related to the borogermanates REBGeO5 with a stillwellite-type structure. Pr3+, ion was used as a local structural probe to corroborate the structural resolution results. Absorption and fluorescence spectra of A(1-x)Pr(x)BP(1-x)Ge(x)O(5) (A = alkaline earth or Pb; x = 0.05) have been investigated at different temperatures. At 9 K the H-3(4) --> (3)p(0) transition of trivalent praseodymium ion (42 configuration) is observed as a Single line. This indicates a unique crystallographic site for the rare earth ion in these compounds replacing the divalent cation. Energy level schemes were deduced from the low-temperature spectroscopic measurements. Comparing the electronic level splittings of studied compounds with the already reported data on REBGeO5 doped with Pr3+ ion, it is possible to dispel the doubt existing about structural determination. Moreover, under 460 nm. excitation, intense red emission of trivalent praseodymium is observed corresponding to D-1(2) --> H-3(4) transition. The lifetime measurements of D-1(2) level have been performed for all the title compounds.