Tunable Thickness and Photoluminescence of Bipyramidal Hexagonal β-NaYF₄ Microdisks

Hexagonal β-NaYF 4 was synthesized as capped bipyramidal microdisks solvothermally from yttria (Y 2 O 3 ), sodium fluoride and ammonium hydrogen fluoride. The microdisks are bound by up to eighteen faces; six {202̅3} facets on both the top and bottom of the disk and six radial {101̅0} facets around its central band. The overall morphology and particle size can be modified through change of temperature or alcoholic solvent, both of which affect the development of the {101̅0} faces. The photoluminescence properties of doped microdisks, such as down-conversion in the case of β-NaYF 4:Eu 3+ or up-conversion for β-NaYF 4:Yb 3+ /Er 3+, were investigated in detail. The lifetime and emission of the Eu 3+ and Er 3+ ions appear related to the morphology of the host crystals. This system provides an excellent example in the tuning and optimization of the optical properties of a material through morphological control via facile change of synthetic conditions.