Pure Near-Infrared Up-Conversion Emission of Tm³⁺ Sensitized by Ni²⁺ in MgGa₂O₄

A series of Ni2+/Tm3+ codoped MgGa2O4 phosphors were prepared using a conventional high-temperature solid-state method. A strong NIR up-conversion emission around 801 nm is exhibited in the Ni2+/Tm3+ codoped MgGa2O4 phosphor under excitation of 1064 nm, with a marked advantage over a blue up-conversion emission near 476 nm, indicating that the Ni2+/Tm3+ codoped MgGa2O4 is an excellent pure NIR to NIR up-conversion phosphor. The NIR up-conversion intensity of the Ni2+/Tm3+ codoped MgGa2O4 can be enhanced by approximately 200 times compared to the Tm3+ single-doped one. It is proven that the energy transfer from Ni2+ to Tm3+ caused by radiative reabsorption performs the up-conversion. The results suggest that the newly developed up-conversion material in the present work may be considered as a candidate for applications such as bioimaging, efficiency enhancement of solar cells, and infrared detection.