Second-order John-Teller distortion in the thermally stable Li(La, Gd) MgWO6:Eu3+ phosphor with high quantum efficiency

Thermally stable Li(La, Gd)MgWO6:Eu3+ phosphors with high quantum efficiency were obtained by the sol-gel method. The symmetry of this double perovskite was reduced by doping Gd3+ ions in order to enhance the luminescence properties. In addition, phase structure and luminescence properties were characterized. A second order John-Teller (SOJT) distortion of WO6 octahedron existed in this double perovskite and was investigated in detail for the first time. The WO6 octahedron of LiLa0.95-xGd(4)Eu(0.05)MgWO(6) distorted gradually and the SOJT distortion started to disappear while x >= 0.7. Intensities of D-5(0)-F-7(2) transition were greatly enhanced and reached the maximum at x = 0.5 under the excitation of 465 nm. The LiLa0.45Gd0.5Eu0.06MgWO6 phosphor showed excellent thermal stability and the thermal quenching mechanism was discussed by the configurational coordinate diagram. The optimized LiGd0.5Eu0.5MgWO6 showed high quantum efficiency, which is much higher than commercial Y2O2S:Eu3+ and Y2O3:Eu3+ phosphors. The synthesized phosphors emit intense red light under the near ultraviolet and have great potential in light emitting diode.