Controlling the white phosphorescence ZnGa2O4 phosphors by surface defects

Abstract White phosphorescence that lasted ≈ 212 s, being the longest phosphorescence time reported so far for any Ga based material, has been observed in undoped ZnGa2O4 (ZGO) phosphors. The samples were synthesized by a simple combustion method by using two different Gallium precursors (Gallium nitrate and Gallium Acetylacetonate). According to the X-ray diffraction analysis, the samples prepared with the two different precursors presented the same single cubic phase. TEM images demonstrated that the ZGO phosphors made with both precursors are formed by nanoparticles with quasi-spherical shape, and they have nanoparticle sizes in the range of 17–43 nm. When excited with UV light (400 nm), these phosphors produced a broad blue-green-yellow luminescence. The blue band was associated to transitions from the Ga-O levels, while that of green-yellow band was attributed to radiative transitions from oxygen vacancies. Particularly, the sample synthesized with Gallium acetylacetone precursor presented the highest phosphorescent emission intensity and had a CIE coordinates of (x = 0.27, y = 0.33), which is close to that for pure white light (x = 0.33, y = 0.33). Since the ZGO presented a white phosphorescent emission without doping with rare earths, they could be good candidates for lighting or signaling applications.