Hydrothermal synthesis combined with calcination of NaGd(SO4)2 nanoparticles and their luminescent properties from single doped Eu3+ and co-doped Yb3+,Er3+

The NaGd(SO4)2: Eu3+/Yb3+,Er3+ nanoparticles were successfully synthesized by a facile hydrothermal method combined with calcination. DTA-TG-DTG, FT-IR, and XRD results reveal that the precursor is composed of gadolinium hydrate with sulfate groups and can convert into pure NaGd(SO4)2 nanoparticles with a dispersed fishing net shape after calcined at 800 °C for 2 h. Upon excitation at 273 nm UV light, the emission spectra of Eu3+-doped phosphors consist of 5D0 → 7Fj (j = 1, 2, 3, 4) transitions and the target NaGd(SO4)2: Eu3+ shows a highest red luminescent intensity than NaGd(SO4)2·H2O: Eu3+ and Gd2O3: Eu3+ phosphors, corresponding to the 5D0 → 7F2 transition of Eu3+. The calculated lifetime of NaGd(SO4)2 is determined to be 2.345 ms. The up-conversion luminescence (UCL) mechanism of Yb3+ and Er3+ co-doped NaGd(SO4)2 and Gd2O3 phosphors were also discussed in the typical energy level diagram for their possible UCL processes.