Controlled growth along circumferential edge and upconverting luminescence of β-NaYF ₄: 20%Yb ³⁺, 1%Er ³⁺ microcrystals

Rational control over the uniform morphology and size of hexagonal NaYF ₄ has been achieved via a facile hydrothermal route. The evolution of particle morphology from peg-top-like to hexagonal microprisms with protruding centers and the long tubelike morphology with concave wedge and finally to solely microrods been demonstrated by increasing the F ^-/Ln ³⁺ molar ratio, all other parameters being equal. Rationally controlling the shape of hexagonal NaYF ₄ is of great importance due to their strongly shape-dependent optical properties. Moreover, the systematic study on the photoluminescence of 20%Yb ³⁺, 1%Er ³⁺-doped β-NaYF ₄ with different shapes shows that the upconversion (UC) properties of these products are strongly dependent on the combined roles of morphologies, crystallinity, and particle sizes. In particular, the microrods evince a better PL signal as compared with others.