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.