Temperature-sensing characteristics of NaGd(MoO4)2: Sm3+, Tb3+ phosphors

In this study, Sm3+/Tb3+-co-doped NaGd(MoO4)2 phosphors were prepared via the hydrothermal method, with sodium citrate used as a chelator. X-ray diffraction confirmed the structure of the samples, and the test outcomes showed that the phosphors exhibited a body-centered tetragonal structure. Field-emission scanning electron microscopy results showed that the specimen morphology changed with the change in the Cit3−/Re3+ molar ratio. Moreover, the measured temperature-dependent emission spectra showed that Sm3+ and Tb3+ had different quenching trends; thus, the fluorescence intensity ratio can be used to represent temperature. In addition, the outcome of this experiment revealed that the temperature-sensing sensitivity of the phosphors gradually increased with the increasing Cit3−/Re3+ ratio, and the highest sensitivity value was 0.346 K−1 (at 503 K, Cit3−/Re3+ = 2). When the temperature was 298–369 K, the temperature-sensing relative sensitivity increased with increasing Cit3−/Re3+, but in the range 374–503 K, the relative sensitivity decreased with increasing Cit3−/Re3+. The highest relative sensitivity value of the sample was 2.7% K−1 (404 K, Cit3−/Re3+ = 0). Additionally, the Commission International del’Eclairage chromaticity coordinates displayed that the luminous colors of Sm3+/Tb3+-co-doped specimens continuously changed from green to red as the temperature changed.