Polarization modulated upconversion luminescence: single particle vs. few-particle aggregates

Luminescence from crystals is often anisotropic and it leads to the polarization behavior of luminescence from single crystalline particles, as exemplified here with the upconversion luminescence from a single NaYF4 nanodisk. Nanodisk aggregates exhibit polarization dependent luminescence with different polarization degrees, which depends on the orientation and distribution of nanoparticles.