Morphology controllable synthesis and upconversion luminescence of Gd4O3F6: Ho3+, Yb3+ for temperature sensing

A series of Yb3+, Ho3+ co-doped Gd4O3F6 with different morphologies (nanoparticles, oval and capsule-like submicrocrystals) and sizes are prepared by a facile hydrothermal route. The results of X-ray diffraction and scanning electron microscopy show that all pH values, organic additives and Li+ concentration play a significant effect on the crystallinity and morphology of the samples. And then, these conditions influence the upconversion (UC) luminescence intensity excited by 980 nm laser without changing the ratio of green and red emitting light obviously. Moreover, after introducing Tm3+, Gd4O3F6: Tm3+, Ho3+, Yb3+ exhibits excellent multicolor emission in the visible region. The corresponding UC mechanisms are elucidated through the laser power dependence of UC emissions. Furthermore, the temperature-dependent UC luminescence of Gd4O3F6: Ho3+, Yb3+ and Gd4O3F6: Tm3+, Ho3+, Yb3+ are investigated, and the results show that the ratio of green to red emission in Gd4O3F6: Ho3+, Yb3+ and Gd4O3F6: Tm3+, Ho3+, Yb3+ both respond single exponentially to temperature, which suggests their application for sense temperature.