Hydrothermal synthesis and green up-conversion luminescence of Yb3+ and Ho3+ co-doped SrGd2(WO4)2(MoO4)2 nanocrystal

In this investigation, the research focuses on the effect of different contents of Yb3+ and different ratios of Yb3+/Ho3+ for the luminescence properties of SrGd2(WO4)2(MoO4)2:Yb3+/Ho3+ nanocrystals. The luminescent nanocrystals were synthesized by the hydrothermal method. The structure and properties of luminescent powder were examined by X-ray diffraction (XRD) scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The crystal structure of SrGd2(WO4)2(MoO4)2:Yb3+/Ho3+ samples, which were characterized by XRD, is the tetragonal system. The particle sizes, which were observed by using SEM and TEM, are between 70 and 80 nm. The luminescence intensity was the strongest while the Yb3+ doping concentration was 6.0 mol. % and Yb3+/Ho3+ = 6:1.5. The green emission peak at 545 nm corresponds to the 5F4(5S2) → 5I8 transition of Ho3+, and the red emission peak at 651 nm corresponds to the 5F5 → 5I8 transition of Ho3+. The log-log plots of luminescence intensity and pump power revealed that red and green emission peaks were the two-photon absorption. The quantum yields of the samples were near 1.7%.