Modifying phase, shape and optical thermometry of NaGdF4:2%Er3+ phosphors through Ca2+ doping

An efficient soft chemistry method to modify the phase, shape and optical thermometry of NaGdF4:2%Er3+ nano-phosphors through doping Ca2+ ion is reported. With the introduction of Ca2+, the phase changes from the GdF3:2%Er3+ to NaGdF4:2%Er3+ was achieved, and the shapes of NaGdF4:2%Er3+ were modified from irregular particles to pure hexagonal NaGdF4 microtubes. These modifications derive from the charge redistribution on the nucleus surface through internal electron charge transport between Gd3+ in a lattice and co-doped Ca2+ ion. An obvious enhancement of the total fluorescence intensity was observed after doping the Ca2+ ion. Moreover, an interesting phenomenon was observed that the fluorescence intensity of the mixed GdF3:2%Er3+ and NaGdF4:2%Er3+ was not be quenched at the high temperature more than 473 K. A maximum relative sensitivity of 0.00213/K (416 K) was obtained at 20%Ca2+ doping. These results indicate that NaGdF4:Er3+/Ca2+ can be applied in optical temperature sensor.