Eu⁺³ and Cr⁺³ doping for red cathodoluminescence in ZnGa₂O₄

Cathodoluminescence emission spectra and photoluminescence (PL) excitation spectra were used to evaluate Eu⁺³ and Cr⁺³ as activators for red luminescence in ZnGa₂O₄. In the ZnGa₂O₄:Eu materials red emission from Eu⁺³ and blue intrinsic emission were observed. The blue intrinsic emission increased relative the Eu⁺³ emission with increasing current density and is attributed to preferential current saturation of the Eu⁺³ activators. In addition, PL excitation measurements revealed that the inefficient energy transfer from the ZnGa₂O₄ host to the Eu⁺³ is due to poor spectral overlap between the ZnGa₂O₄ emission and the Eu⁺³ absorption. Cr-doping resulted in a saturated red-color, and no host emission was observed over the entire current density regime investigated. The PL excitation of the ZnGa₂O₄:Cr revealed good overlap between the ZnGa₂O₄ host and the Cr⁺³ absorption. Efficient energy transfer to the Cr⁺³ activators occurs via multipolar interactions.