Preferential occupancy of Eu and energy transfer in Eu doped SrVO, SrGd(VO) and SrVO/SrGd(VO) phosphors.

The vanadate-based phosphors SrVO:Eu (SV:Eu), SrGd(VO):Eu (SGV:Eu) and SrGd(VO)/SrVO:Eu (SGV/SV:Eu) were obtained by solid-state reaction. The bond-energy method was used to investigate the site occupancy preference of Eu based on the bond valence model. By comparing the change of bond energy when the Eu ions are incorporated into the different Sr, V or Gd sites, we observed that Eu doped in SV, SGV or SV/SGV would preferentially occupy the smaller energy variation sites, , Sr4, Gd and Gd sites, respectively. The crystal structures of SGV and SV, the photoluminescence properties of SGV:Eu, SV, SGV/SV and SGV/SV:Eu, as well as their possible energy transfer mechanisms are proposed. Interesting tunable colours (including warm-white emission) of SGV/SV:Eu can be obtained through changing the concentration of Eu or changing the relative quantities of SGV to SV by increasing the calcination temperature. Its excitation bands consist of two types of O → V charge transfer (CT) bands with the peaks at about 325 and 350 nm respectively, as well as f-f transitions of Eu. The obtained warm-white emission consists of a broad photoluminescence band centred at about 530 nm, which originates from the O → V CT of SV, and a sharp characteristic spectrum (D-F) at about 615 and 621 nm.