Improving the Luminescence Intensity and Lifetime of Near‐Infrared Luminescent Nanoparticles by Protected Calcination

ABSTRACT Thanks to their deep tissue penetration and low background signal compared to visible light, near‐infrared (NIR) emitting nanomaterials have gained significant interest for their potential application in fluorescence bioimaging. However, there are many obstacles that stand in the way of fluorescence imaging, such as tissue autofluorescence and low luminescence efficiency of the contrast agents. In this work, a number of these obstacles are tackled by a protected calcination process performed on GdVO 4 :Nd 3+ NIR‐emitting luminescent nanoparticles. This method produces nanoparticles with high crystallinity due to the calcination, resulting in minimal defect‐related non‐radiative decay. It also applies a silica shell onto the nanoparticles, with control over the shell thickness. The silica shell shields the excited Nd 3+ ions from coupling with ─OH groups in water and prevents the GdVO 4 :Nd 3+ cores from aggregating upon calcination, thus ensuring colloidal stability upon partial shell removal. The protected calcination process was performed on GdVO 4 :Nd 3+ nanoparticles as prepared by a hydrothermal method, enhancing the luminescence intensity by over an order of magnitude and increasing the luminescence lifetime from 5.5 to 47.7 µs, while retaining an average size of below 100 nm.