title: Strain-induced modification of optical selection rules in lanthanide-based upconverting nanoparticles.
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.
authors: Department of Materials Science and Engineering, Stanford University , Stanford, California 94305, United States.
authors: Michael D
authors: MD
authors: Wisser
authors: Maverick
authors: M
authors: Chea
authors: Yu
authors: Y
authors: Lin
authors: Di M
authors: DM
authors: Wu
authors: Wendy L
authors: WL
authors: Mao
authors: Alberto
authors: A
authors: Salleo
authors: Jennifer A
authors: JA
authors: Dionne
keywords: Upconversion; crystal field theory; diamond anvil cell; excited-state lifetimes; lanthanides; optical selection rules