Magnetic field modulated upconversion luminescence in NaYF4:Yb,Er nanoparticles

Upconversion, an anti-Stokes process that converts two or more lower energy photons into a higher energy photon, has been paid growing attention due to its wide range of applications ranging from photonics to bioscience. This process, however, suffers from poor efficiency which strongly hampers its application and commercialization. We show here that the upconversion luminescence of NaYF4:Yb,Er nanoparticles can be modulated by the magnetic field and an enhancement of upconversion intensity by a factor of 2.5 is obtained at 20 T. The increased upconversion luminescence is interpreted in terms of enhanced energy transfer from Yb3+ to Er3+ and the enhanced non-radiative transition from 4S3/2 to 4F9/2 and 4I11/2 to 4I13/2 of Er3+ ions. In addition, continuous spectral broadening and shift of f–f transitions with increasing magnetic field intensity are observed, which are ascribed to the Zeeman effect and the difference in the g factor of Zeeman levels. The results demonstrated here may open a new gate towards the modulation of the excited state process by the magnetic field.