Optical temperature sensing properties of Er3+, Yb3+ co-doped NaGd(MoO4)2 phosphor

Er3+, Yb3+ co-doped NaGd(MoO4)2 phosphors by using sodium citrate as chelating agent were synthesized by hydrothermal method. The structure and morphology were characterized by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The temperature-dependent up-conversion spectra of Er3+, Yb3+ co-doped NaGd(MoO4)2 phosphor under the excitation of 980 nm laser with different ratios of Cit3−/Re3+ has been measured. It was found that the Cit3−/Re3+ ratio considerably influenced the sample's morphology. The temperature sensing performance for the samples with various morphologies 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 sensitivity can up to a relative high value of 0.0161 K−1, which was obtained for the sample with the ratio of Cit3−/Re3+ was 0.5. Finally, physical mechanism of morphology-dependent temperature sensing sensitivity was explained and predicted.