ESR Investigation of a [Cr(V)O₄Pb₈] Center in PbMoO₄. Origin of the Yellow Coloration of Lead Molybdate

Abstract

The ESR spectra of Cr doped PbMoO, originate from CrOi-ions at normal MovI sites with a dZz ground state interacting with z07Pb nuclei of two sets of four first-neighbour lead sites. The principal values and the directions of the principal axes of the two Cr5+-Pb2+ hf tensors are determined and discussed according t o the nature of the cation-cation interactions. The temperature dependence of the spectrum intensity, which falls to zero outside the 10 to 45 K region is explained as a combination of a very short Cr5+ spin lattice relaxation time and a long spin diffusion time. The yellow coloration of oxidized samples of PbMoO, (Cr) results from the existence of an intense line (f = 0.14)in its absorption spectrum peaking a t 430 nm. This band is attributed to a charge transfer transition of Ci-0;-ions which is red shifted from its normal position in most chromates because of a mixing with a Pb2+ -Cr6+ intervalence transition.Le spectre R P E de PbMoO, dope au chrome a 6tk attribue B un ion C r O r en site MovI possbdant un &at fondamental de type dzz en interaction avec les noyaux c07Pb des deux groupes de plomb premiers-voisins. Les valeurs principales e t les directions principales des deux tenseurs hyperfins Cr5+-Pb2+ ont At& dkterminkes et discutees en fonction de la nature des interactions cation-cation.

First‐principles study of the electronic structures and absorption spectra for the PbMoO4 crystal with lead vacancy

“…The yellowish colour of as-grown PMO crystals has been found to be associated with an absorption band peaking at 430 nm [9]. This coloration has been ascribed to deviations from stoichiometry [10] or the presence of impurities [11,12].…”