Direct cation exchange of surface ligand capped upconversion nanocrystals to produce strong luminescence

We develop a facile and rapid cation exchange method for upconversion nanocrystals (UCNCs) without removing surface ligands. It avoids the tedious pretreatment of as-synthesized UCNCs, and the luminescent intensities of nanocrystals after Tb3+ exchange using the new method are much stronger than those of the nanocrystals obtained using conventional cation exchange in water.