Hydrothermal synthesis, structural and luminescent properties of a Cr3+ doped MgGa2O4 near-infrared long lasting nanophospor

A novel long lasting phosphor MgGa2O4:Cr3+ was successfully prepared by a hydrothermal method and a solid state reaction method. The hydrothermal method provides nanoparticles of the range 10-70 nm. XRD, FTIR spectroscopy, HRTEM, FESEM, photoluminescence, UV-VIS spectroscopy, and phosphorescence decay measurements were utilized to characterize the phosphor. MgGa2O4 possesses a cubic phase and the Fd3m space group. It crystallizes in a normal spinel structure with Mg2+ ions in tetrahedral coordination and Ga3+ ions in octahedral coordination. The phosphor showed three excitation bands at 225 nm, 445 nm and 558 nm. Upon UV excitation at 225 nm, the material exhibited an emission band from 600-800 nm peaking at 707 nm corresponding to the E-2((2)G) -> (4)A(2)(F-4) spin forbidden transition of the distorted Cr3+ ions in the MgGa2O4 host. Three deconvoluted peaks at 675 nm, 707 nm and 733 nm were found in phosphorescence emission spectra. The decay curve shows that the sample prepared by the solid state reaction method undergoes a sharper decay process than the samples prepared by the hydrothermal method. Slow decay was observed for the sample with lowest concentration. A significant afterglow signal was observed for 1 hour when the sample was excited at 225 nm for 5 minutes. This nanophosphor with an emission band at 600-800 nm can be suitable for in vivo bio imaging application purposes.