Solid-to-Hollow Single-Particle Manipulation of a Self-Assembled Luminescent NaYF4:Yb,Er Nanocrystal Monolayer by Electron-Beam Lithography

A facile method to fabricate NaYF4:Yb,Er hollow structures from an assembled solid NaYF4:Yb,Er nanocrystal monolayer by electron-beam lithography, was investigated. Hollow structures of β-NaYF 4:Yb,Er were formed in situ under the electron-beam irradiation operated in TEM from the assembly of nanocrystal monolayers. The electron beam is operated with an electron-gun emission current of 46 μA, and focused in an area of less than 1 cm2 on the fluorescent screen in TEM. The particle size does not change prominently, which is different from the obvious size increase that occurs in the Kirkendall effect. X-ray analysis spectra show that the elemental composition of the manocrystals does not change after electron-beam irradiation, and the SAED pattern also corresponds well with hexagonal NaYF4. Because the hollow structure only forms under electron beam irradiation, the operation can be performed on a selected single particle by simply focusing the electron beam into a small region.