Crystalline Hollow Microrods for Site-Selective Enhancement of Nonlinear Photoluminescence.

A class of one-dimensional hollow microstructure is described, which was formed by a kinetically controlled crystal growth process. A hexagonal-phase NaYbF microrod comprising isolated holes along the longitudinal axis was synthesized by a one-pot hydrothermal method with the assistance of citrate ligands. The structural void feature modulates light intensity across the microrods as a result of interference arising from light scattering and reflection by the inner walls. A single crystal comprising a structural void was doped with upconverting lanthanide ions. Upon near-infrared excitation of the doped crystal spatially resolvable optical codes were produced.