Optimization of Chromium-Doped Zinc Gallate Nanocrystals for Strong Near-Infrared Emission by Annealing

Chromium-doped spinel crystals show long-lasting emissions in the near-infrared wavelength region. The emission can be activated by X-ray or ultraviolet-visible (UV-visible) light. Such properties make this material a promising candidate for background-free deep-tissue bioimaging, photodynamic or photon induced therapy, and other applications. Here, we apply hydro thermal synthesis for the preparation of Cr-doped zinc gallate (ZnGa2O4) nanoparticles of small sizes with around 10 nm in diameter, which has the potential to be intravenously introduced to patients. We find that annealing of the as-prepared nanoparticles at 800 ? yields an order of magnitude increase in the emission intensity in the near-infrared wavelength region upon X-ray exposure with favorable long-lasting photoluminescence, which may be directly employed for deep-tissue cancer treatments when combined with IR700-mAb conjugate drug agents. We discuss the effect of annealing on the structural changes and the evolution of Cr defects of 10 nm Cr-doped zinc gallate nanoparticles by imaging techniques and monitoring their magneto-optical signals.