Upconversion luminescence of lanthanide-doped mixed CaMoO4-CaWO4 micro-/nano-materials

Upconversion nanoparticles (UCNPs) have been reported to have very efficient applications in both biological field and non-biological field, because of the unique NIR-triggered anti-Stokes emissions. Molybdates and tungstates with essentially identical crystal structure (scheelite structure) have excellent thermal and luminescence properties, which are widely used in phosphors, scintillators, optical fibers, gas sensors, and so on. Scheelites are very attractive as green emitting components for white LEDs because of their high fluorescence efficiency. Various tungstate and molybdate materials of the RE2(MO4)3, RE2MO6, REY(MO4)2 type (RE = rare earth, M = W or Mo) have already been reported, yet mixtures of rare-earth tungstate and molybdate materials at the micro-/nano- size are a less explored class of materials. Therefore this work focuses on mixed tungstate-molybdate materials. Here we report Er3+/Yb3+ doped CaMoO4-CaWO4 mixed upconversion materials synthetized by a hydrothermal method. Before heat treatment, the materials show relatively weak green light under excitation at 975 nm; after heat treatment, the intensity of upconversion luminescence increases dramatically. By adjusting the molybdate/tungstate ratio, we have been able to establish that the molybdate content is the dominant factor influencing the luminescence intensity of the upconversion materials.