Strain-induced modification of optical selection rules in lanthanide-based upconverting nanoparticles.

Wisser, Michael D; Chea, Maverick; Lin, Yu; Wu, Di M; Mao, Wendy L; Salleo, Alberto; Dionne, Jennifer A · Nano Lett · 2015

basic_science · Level V

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Abstract

NaYF4:Yb(3+),Er(3+) nanoparticle upconverters are hindered by low quantum efficiencies arising in large part from the parity-forbidden nature of their optical transitions and the nonoptimal spatial separations between lanthanide ions. Here, we use pressure-induced lattice distortion to systematically modify both parameters. Although hexagonal-phase nanoparticles exhibit a monotonic decrease in upconversion emission, cubic-phase particles experience a nearly 2-fold increase in efficiency. In-situ X-ray diffraction indicates that these emission changes require only a 1% reduction in lattice constant. Our work highlights the intricate relationship between upconversion efficiency and lattice geometry and provides a promising approach to modifying the quantum efficiency of any lanthanide upconverter.