SCHEDULED MAINTENANCE
Upconversion improvement by the reduction of Na+-vacancies in Mn2+ doped hexagonal NaYbF4:Er3+ nanoparticles
Abstract
Hexagonal-phase NaYbF4:Er3+ 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:Er3+ UCNPs, has been achieved by Mn2+ doping. The underlying reason for luminescence enhancement by Mn2+ 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 Mn2+ substitution disturbs the equilibrium of the charge and crystal lattice in the hexagonal-phase NaYbF4:Er3+ UCNPs, which makes the Na+-vacancies that quenched luminescence become filled with Na+ or Mn2+ to offset the imbalance of the charge and electron cloud distortion. In addition, the Mn2+ 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 Mn2+-doping approach provides a facile strategy for improvement of luminescence, which will impact on the field of bioimaging based on UCNP nanoprobes.
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