UC Berkeley

The small absorption cross sections (ϵ < 10 M-1 cm-1) characteristic of Laporte-forbidden transitions in the f-elements have limited the practical implementation of lanthanide nanoparticles in solar capture devices. While various strategies designed to circumvent the problems of low f-f oscillator strengths have been investigated, comparatively little work has explored the utility of organic ligands with high absorption coefficients (ϵ ≈ 103-105 M-1 cm-1) in sensitizing excited states in lanthanide nanocrystals. Here, we detail the photophysics of NaGd1-xEuxF4 nanoparticles featuring surface display of the ligand 3,4,3-LI(1,2-HOPO), an aromatic antenna functioning as the terminal light absorber in this system. The result is a ligand-nanocrystal hybrid that converts UV (250-360 nm) light into red Eu(III) luminescence with an external quantum yield of 3.3%. We analyze this sensitization process, responsible for a 104-fold increase in luminescence relative to metal-centered excitation, through a quantitative treatment of energy transfer between ligand and metal states.