NaLuF4:Yb3+, Er3+ bifunctional microcrystals codoped with Gd3+ or Dy3+ ions: Enhanced upconversion luminescence and ferromagnetic-paramagnetic transition

Here, NaLuF4:Yb3+/Er3+/Gd3+ bifunctional microcrystals were successfully synthesized by hydrothermal method, which can emit similar to 652 nm red light from Er3+-4f(n) electronic transition F-4(9/2)-I-4(15/2) and similar to 542 nm green light from Er3+-4f(n) electronic transition S-4(3/2)-I-4(15/2), under the excitation of 980 nm infrared light. The intensity ratio of red to green emission increases obviously with increasing the concentration of Gd3+ from 0 mol% to 10 mol%. Meanwhile, the red shift is also observed which is ascribed to the difference in surface property. By introducing Dy3+ ion into NaLuF4:Yb3+/Er3+, the intensity of both green and red emissions changes non-monotonously due to the energy exchange between Er3+ and Dy3+, which reaches to the highest value when doping with 0.5 mol% Dy3+ ion. The ferromagnetic property decreases with increasing the concentration of Gd3+ ion while the paramagnetic property increases greatly. This is ascribed to the fact that the coexistence of light rare earth (Gd3+) and heavy rare earth (Yb3+/Tm3+) will lead to the anti-ferromagnetic coupling in the sub-lattices. (C) 2016 Published by Elsevier B.V.