Enhanced luminescence properties of ZnGa2O4:Cr3+ nanoparticles with an average crystallite size of 5 nm

ZnGa₂O₄:Cr³⁺ nanophosphors with an average crystallite size of 5 nm were prepared by a combustion method. We observed changes in the luminescence properties compared with the micro-crystalline system, such as a high brightness emission band at 696 nm and a decrease in the persistent luminescence decay time for the near-infrared emission. The system does not show a change in the band gap. The emission intensity for the broad band with near-infrared emission was very high under excitation with both UV and visible wavelengths.

The system presents good stability in colloidal suspensions in water and phosphate-buffered saline, which were found to conserve the luminescence properties.

The system is non-toxic and shows applications for in vivo optical imaging due to the rather high penetration depth of near-infrared radiation into human tissue. Its small crystallite size enables it to enter cells for bioimaging, exhibit good dispersion in a biological environment and resist photobleaching.