Multi-site occupancies of Eu2+ in Ca6BaP4O17 and their potential optical thermometric applications

Single Eu2+ doped Ca6BaP4O17 materials are demonstrated to show potential optical thermometric applications with doping concentration-dependent luminescence and temperature-sensitive luminescence. Eu2+ ions occupy three types of lattice sites based on the results of Rietveld refinements, VUV-UV-vis (vacuum ultraviolet ultraviolet - visible) luminescence spectra and time-resolved emission spectra. Due to site occupation and energy transfer, the emission color of Eu2+ doped Ca6BaP4O17 materials is tunable with the variation of the doping concentration of Eu2+. Then the energy transfer mechanism is analyzed using Inokuti-Hirayama, Yokota-Tanimoto, and Burshtein models, respectively. Because of the different thermal behaviors of Eu2+ luminescence in Ba2+, Ca2+(1) and Ca2+(2) sites, Ca6BaP4O17: Eu2+ phosphors appear obvious emission intensity evolutions with the increase of temperature, accompanying with the change of emission color under excitation at 300 and 400 nm, respectively. It indicates that Eu2+ doped Ca6BaP4O17 phosphors possess temperature sensitive luminescence characteristics. The temperature-dependent ratiometric emission intensity and the temperature recycle measurements verify the possibility of optical thermometric applications of Ca6BaP4O17: Eu2+ phosphors.