Toward Upconversion Luminescence Enhancement with Dye Sensitization

Upconversion nanoparticles (UCNPs) containing lanthanide have attracted considerable attention in the applications of bioimaging, phototherapy, biosensing, solar cells, etc., because of their unique large anti-Stokes luminescence. However, the low upconversion luminescence (UCL) efficiency due to the narrow and weak absorption of lanthanide ions fundamentally restricts their applications. Sensitized UCNPs with dyes are expected to break this limitation, which could yield to 5 orders of magnitude UCL enhancement. The strategy of dye-sensitized UCNPs has broadened upconversion excitation bands, where the dyes efficiently harvest near-infrared light and transfer the energy to lanthanide ions. Benefiting from the sensitizing process of dyes, the brightness was enhanced by 1000 times. In this paper, we summarize the most recent advances on sensitized UCNPs with an antenna effect from different dyes, with an emphasis on the sensitization mechanism and the geometric classification of the dyes. In addition, the perspectives and challenges of sensitized UCNPs are also discussed.