Remarkable red-shift of upconversion luminescence and anti-ferromagnetic coupling in NaLuF_4：Yb~（3＋）/Tm~（3＋）/Gd~（3＋）/Sm~（3＋） bifunctional microcrystals
摘要
Lanthanide doped bifunctional materials are potentially important for developing multifunctional devices. Here, NaLuF_4：Yb~（3＋）/Tm~（3＋）/Gd~（3＋）/Sm~（3＋） optical-magnetic bifunctional microcrystals were successfully synthesized by hydrothermal method, which could emit ~480 nm blue light from the ~1G_4→~3H_6 electronic transition and ~800 nm infrared light from the ~3H_4→~3H_6 electronic transition of Tm~（3＋） ion, under the excitation of 980 nm infrared light. By doping Sm~（3＋） ion into Na Lu F4：Yb~（3＋）/Tm~（3＋）/Gd~（3＋）, the infrared emission peak centered at 800 nm would shift obviously to longer wavelength. This indicated that Sm~（3＋） ion could efficiently tune the energy level gaps of Tm~（3＋） ions in Na Lu F4 host which was demonstrated based on the crystal field theory. In addition, these NaLuF_4：Yb~（3＋）/Tm~（3＋）/Gd~（3＋）/Sm~（3＋） microcrystals presented unique ferromagnetic property instead of usually reported paramagnetic property. Importantly, the ferromagnetic property decreased with increasing the concentration of Gd~（3＋） ion. This was in good agreement with Swift＇s theoretical investigation that the coexistence of light rare earth（Gd~（3＋）） and heavy rare earth（Yb~（3＋）/Tm~（3＋）） would lead to the anti-ferromagnetic coupling in the sub-lattices.