The hydrothermal synthesis and morphology-dependent optical temperature sensing properties of Er3+ doped NaGd(WO4)2 phosphor

NaGd(WO4)2: Er3+ phosphors by using sodium citrate (Na3Cit, Na3C6H5O7) as chelating agent were synthesized via hydrothermal method. The structure and morphology were characterized and analyzed by the X-ray diffraction and field emission scanning electron microscopy. It was found that Na3Cit added into the reaction solution considerably influenced the morphologies of samples. The temperature-dependent down-conversion emission spectra of NaGd(WO4)2: Er3+ phosphor under the excitation of 377.5 nm fluorescence with different ratios of Cit3-/Re3+ have been measured. The temperature sensing performance for the samples was studied based on the change of emission intensities from two thermally coupled 2H11/2 and 4S3/2 levels of Er3+. It was found that the temperature sensing sensitivities increased with the increase of ratios of Cit3-/Re3+, and the temperature sensing sensitivity can reach a relatively high value of 0.0128 K−1, which was obtained for the sample with the ratio of Cit3-/Re3+ was 1.5. Finally, the physical mechanism of morphology-dependent temperature sensing sensitivity change was explained.