  Photoinduced reductions in the oxygen vacancy concentration were leveraged to
increase the ferroelectric phase fraction of $\mathrm{Hf_{0.5}Zr_{0.5}O_2}$
(HZO) thin-films. Modest ($\sim 0.02-0.77~\mathrm{mJ/\mu m^2}$) laser doses of
visible light (488 nm, 2.54 eV) spatially patterned the concentration of oxygen
vacancies as monitored by photoluminescence imaging. Local, tip-based,
near-field, nanoFTIR measurements showed that the photoinduced oxygen vacancy
concentration reduction promoted formation of the ferroelectric phase (space
group $Pca2_1$) resulting in an increase in the piezoelectric response measured
by piezoresponse force microscopy. Photoinduced vacancy tailoring provides,
therefore, a spatially prescriptive, post-synthesis, and low-entry method to
modify phase in \hfo-based materials.
