Color-tunable emissions and multi-mode optical thermometer in Mg3Gd2Ge3O12: Tb3+, Eu3+ phosphors

A series of Mg3Gd2Ge3O12 phosphors co-doped with Tb3+ and Eu3+ was produced using a solid-state method. The phosphors doped solely with Tb3+ have blue emission (383 nm) and green emission (544 nm), and the addition of Eu3+ can produce red emission (610 nm). The transformation of green-orange could be achieved by adjusting the doping amount of Eu3+ because of the energy transfer (ET) from Tb3+ to Eu3+. The ET process was attributed to dipole-dipole interaction. In addition, the emission intensities of three levels and the lifetimes of 5D3 decrease with increasing temperature, and the color changes are produced. According to these interesting phenomena, a optical thermometer with different modes was designed utilizing the fluorescence intensity ratio (FIR) and the fluorescence lifetime (FL) model. The maximum values of relative sensitivity (Sr) were found to be 1.24% K-1 at 494 K (FIR = I383/I610), 0.43% K-1 at 423 K (FIR =I544/I610) and 1.38% ms∙K-1 at 465 K (FL). The great repeatability of samples can be got by cyclic testing. The above results demonstrate that Mg3Gd2Ge3O12: Tb3+, Eu3+ samples are potential materials for visual optical temperature measurement.