Tunable luminescence properties of the novel Tm3+- and Dy3+-codoped LiLa(MoO4)(x)(WO4)(2-x) phosphors for white light-emitting diodes

摘要

A series of Tm3+- and Dy3+-codoped LiLa(MoO4)(x)(WO4)(2-x) phosphors were prepared via the conventional solid-state reaction method. It was discovered that the optimum single doped concentrations of both Tm3+ and Dy3+ are 0.04 for the LiLa(WO4)(2) host; moreover, LiLa(WO4)(2):0.04Tm(3+) and LiLa(WO4)(2):0.04Dy(3+) emit blue and yellow light, respectively. On the other hand, the emission colors of Tm3+ - and Dy3+-codoped LiLa(WO4)(2) could be tuned from blue to white by tuning the energy transfer. With increase in the Dy3+ doped concentration, the energy transfer efficiency of LiLa(WO4)(2):0.005Tm(3+), yDy(3+) increased gradually and reached as high as 88% when the concentration of Dy3+ was 0.05. The energy transfer from Tm3+ to Dy3+ was revealed to be resonant via the quadrupole-quadrupole mechanism. As for LiLa(MoO4)(x)(WO4)(2-x):0.005Tm(3+), 0.03Dy(3+) phosphors, the emission intensities of both Tm3+ and Dy3+ were found to reach a maximum when the molar ratio of Mo/W was 0 : 2. In addition, with increase in the proportion of MoO42-, the location of the chromaticity coordinates changed from the edge to the center of the white area. When the relative ratio of Mo/W was 2 : 0, the chromaticity coordinates were much closer to the standard chromaticity coordinates for white light. The results indicate that these phosphors may have potential applications in the fields of UV-excited white light-emitting diodes.