Optical properties and electronic band structure of BiMg₂PO₆, BiMg₂VO₆, BiMg₂VO₆:Pr³⁺ and BiMg₂VO₆:Eu³⁺

The luminescence properties of the yellow pigment BiMg₂VO₆ are revisited and those of BiMg₂PO₆, BiMg₂VO₆:Pr³⁺ and BiMg₂VO₆:Eu³⁺ are described. It is shown that the undoped systems exhibit broad band emission in the green or orange spectral regions, but only upon UV or near UV excitation. In contradiction with a previous report, we found that the blue, host absorbed, photons are lost non-radiatively and do not contribute to the luminescence processes in BiMg₂VO₆. To understand these experimental results, the optical properties of BiMg₂VO₆ and BiMg₂PO₆ are theoretically analysed on the basis of electronic structure diagrams calculated by the DFT method. It is found that the optical transitions are mostly localised within [VO₄]^3- units or non-regular Bi³⁺ ions and occur in the UV or near UV regions. The luminescence of the trivalent lanthanide dopants is weak (Eu³⁺) or unobserved (Pr³⁺) in BiMg₂VO₆ which is explained by inefficient energy migration in the host lattice to the impurity sites.