Up-conversion luminescence polarization control in Er³⁺-doped NaYF₄ nanocrystals

We propose a femtosecond laser polarization modulation scheme to control the up-conversion (UC) luminescence in Er³⁺-doped NaYF₄ nanocrystals dispersed in the silicate glass. We show that the UC luminescence can be suppressed when the laser polarization is changed from linear through elliptical to circular, and the higher repetition rate will yield the lower control efficiency. We theoretically analyze the physical control mechanism of the UC luminescence polarization modulation by considering on- and near-resonant two-photon absorption, energy transfer up-conversion, and excited state absorption, and show that the polarization control mainly comes from the contribution of near-resonant two-photon absorption. Furthermore, we propose a method to improve the polarization control efficiency of UC luminescence in rare-earth ions by applying a two-color femtosecond laser field.