Interplay between chromium content and lattice disorder on persistent luminescence of ZnGa2O4:Cr3+ for in vivo imaging

In the quest of bright and long persistent far-red/near-infrared phosphors for in vivo optical imaging, the interest in the family of ZnGa2O4 spinel compounds doped with Cr3+ has been aroused in the most recent years. We show that the dopant concentration plays an important role in the total persistent luminescence output of the material. ZnGa2O4 doped with 0.25%, 0.50% and 0.75% Cr relative to (Ga+Cr) was prepared by solid state synthesis. 0.50% Cr was found optimal to obtain the most intense persistent luminescence after matrix excitation with X-rays or localized excitation in Cr3+ absorption band with 550 nm wavelength. Up to 0.5% Cr content, persistent luminescence increases as a consequence of an increased number of Cr3+ luminescent centers and associated defects. With 0.75% Cr content, a too large number of defects locally concentrated around Cr3+ ions are detrimental to the long-term persistent luminescence intensity. We supplement long lasting phosphorescence investigation with laser excited photoluminescence and thermally stimulated luminescence results.