Magnetic field enhanced upconversion luminescence and magnetic–optical hysteresis behaviors in NaYF4: Yb, Ho nanoparticles

Abstract

Upconversion, an anti-Stokes process converting two or more low energy photons into a high energy photon, has received much attention due to its wide applications ranging from photonics to medicine. As a nonlinear optical process, the efficiency of upconversion is inherently low, which strongly limits the applications of upconversion. Here we report the enhancement of upconversion luminescence in NaYF₄: Yb, Ho nanoparticles with a pulse magnetic field. The intensity of emissions from ⁵S₂, ⁵F₄ → ⁵I₈, ⁵F₅ → ⁵I₈ and ⁵S₂, ⁵F₄ → ⁵I₇ transitions has been increased 1.71, 1.93, 1.68 times respectively. The enhanced emission has been ascribed to the enhanced energy transfer from Yb³⁺ to Ho³⁺ with increasing magnetic field intensity. Besides, the magnetic–optical hysteresis behaviors of upconversion luminescence intensity have also been observed when the magnetic field was scanned from 0 T to 40 T. This is connected with the sluggish kinetics of spin re-orientation of the paramagnetic lanthanide ions in the pulse magnetic field. The magnetic field modulated upconversion luminescence demonstrated here might provide a new approach to enhance the upconversion efficiency.