title: Upconversion improvement by the reduction of Na⁺-vacancies in Mn²⁺ doped hexagonal NaYbF₄:Er³⁺ nanoparticles.
abstract: Hexagonal-phase NaYbF4:Er(3+) upconversion nanoparticles (UCNPs) have been synthesized via a co-precipitation method in high-boiling-point solvents, and remarkably enhanced upconversion luminescence, particularly in red emission bands (650-670 nm) in NaYbF4:Er(3+) UCNPs, has been achieved by Mn(2+) doping. The underlying reason for luminescence enhancement by Mn(2+) doping is explored by a series of controlled experiments, and a mechanism of enhancement based on the decrease of Na(+)-vacancies and organic adsorption is proposed. The Mn(2+) substitution disturbs the equilibrium of the charge and crystal lattice in the hexagonal-phase NaYbF4:Er(3+) UCNPs, which makes the Na(+)-vacancies that quenched luminescence become filled with Na(+) or Mn(2+) to offset the imbalance of the charge and electron cloud distortion. In addition, the Mn(2+) doping at the surface of UCNPs could reduce the organic adsorption on the surface of the UCNPs by an extra F(-) ion on the grain surface resulting in luminescence enhancement. Therefore, the Mn(2+)-doping approach provides a facile strategy for improvement of luminescence, which will impact on the field of bioimaging based on UCNP nanoprobes.
authors.affiliation: School of Materials & Mineral Resources, Xi'an University of Architecture and Technology, Xi'an, Shaanxi 710055, China. dptian@xauat.edu.cn gaodangli@163.com.
authors.forename: Dongping
authors.initials: D
authors.lastname: Tian
authors.forename: Dangli
authors.initials: D
authors.lastname: Gao
authors.forename: Bo
authors.initials: B
authors.lastname: Chong
authors.forename: Xuanzuo
authors.initials: X
authors.lastname: Liu