Remarkable red-shift of upconversion luminescence and anti-ferromagnetic coupling in NaLuF4:Yb3+/Tm3+/Gd3+/Sm3+bifunctional microcrystals

Lanthanide doped bifunctional materials are potentially important for developing multifunctional devices. Here, NaLuF4:Yb3+/Tm3+/Gd3+/Sm3+optical-magnetic bifunctional microcrystals were successfully synthesized by hydrothermal method, which could emit ∼480 nm blue light from the 1G4→3H6electronic transition and ∼800 nm infrared light from the 3H4→3H6electronic transition of Tm3+ion, under the excitation of 980 nm infrared light. By doping Sm3+ion into NaLuF4:Yb3+/Tm3+/Gd3+, the infrared emission peak centered at 800 nm would shift obviously to longer wavelength. This indicated that Sm3+ion could efficiently tune the energy level gaps of Tm3+ions in NaLuF4host which was demonstrated based on the crystal field theory. In addition, these NaLuF4:Yb3+/Tm3+/Gd3+/Sm3+microcrystals presented unique ferromagnetic property instead of usually reported paramagnetic property. Importantly, the ferromagnetic property decreased with increasing the concentration of Gd3+ion. This was in good agreement with Swift's theoretical investigation that the coexistence of light rare earth (Gd3+) and heavy rare earth (Yb3+/Tm3+) would lead to the anti-ferromagnetic coupling in the sub-lattices.