  Polarized upconversion luminescence (PUCL) of lanthanide (Ln3+) ions has been
widely used in single particle tracking, microfluidics detection,
three-dimensional displays, and so on. However, no effective strategy has been
developed for modulating PUCL. Here, we report a strategy to regulate PUCL in
Ho3+-doped NaYF4 single nanorods based on the number of upconversion photons.
By constructing a multiphoton upconversion system for Ho3+, we regulate the
degree of polarization (DOP) of PUCL from 0.6 for two-photon luminescence to
0.929 for three-photon upconversion luminescence (UCL). Furthermore, our
strategy is verified by cross-relaxation between Ho3+ and Yb3+, excitation
wavelength, excitation power density, and local site symmetry. And this
regulation strategy of PUCL has also been achieved in Tm3+, where DOP is ranged
from 0.233 for two-photon luminescence to 0.925 for four-photon UCL. Besides,
multi-dimensional anti-counterfeiting display has been explored with PUCL. This
work provides an effective strategy for the regulation of PUCL and also
provides more opportunities for the development of polarization display,
optical encoding, anti-counterfeiting, and integrated optical devices.
