Analysis of spectra of neat and lanthanide ion-doped KPb2Cl5 excited by synchrotron radiation

The excitation and emission spectra of neat K2PbCl5, and also doped with the lanthanide ions Pr3+, Nd3+, Er3+ and Tm3+ have been recorded at temperatures down to 10?K using synchrotron radiation. To facilitate the spectral assignments, a first principles calculation has been performed and despite its inaccuracies it confirms the nature of the lower energy levels of this system. The lowest energy transitions in the excitation spectrum are Pb2+-centred, whereas the band gap transitions, which are essentially of a charge transfer (CT) nature, are at shorter wavelengths. The emission transitions are likewise assigned to those from the Pb2+ 3P1,0 states, and from the band gap. The Stokes shift of the latter transition is similar to 18?000?cm-1. Under synchrotron radiation excitation, the energy transfer from the host or Pb2+ levels to 4fN lanthanide ion levels is not efficient.