The synthesis of luminescent crystals based on hexagonal-phase sodium yettrium fluoride upconversion microrods is reported by A/P Liu Xiaogang’s group. The synthetic procedure involves an epitaxial end-on growth of upconversion nanocrystals comprising different lanthanide activators onto the NaYF4 microrods. This bottom-up method readily affords multicolor-banded crystals in gram quantity by varying the composition of the activators. Importantly, the end-on growth method using one-dimensional microrods as the template enables facile multicolor tuning in a single crystal, which is inaccessible in conventional upconversion nanoparticles. These novel materials offer opportunities as optical barcodes for anti-counterfeiting and multiplexed labeling applications.
