Tunable color emission of ZnGa2O4:Si4+ phosphors with enhanced brightness due to donor formation

X-ray diffraction (XRD), Raman scattering, and photoluminescence (PL) measurements were carried out to investigate the structural and optical properties of ZnGa2O4:Si4+ phosphors. The results of the XRD measurements showed that the solid solubility limit of the Si in the ZnGa2O4 phosphors was 0.05 mole fraction. The results of the Raman spectra showed that a new peak at 540 cm−1 in the ZnGa2O4:Si0.074+ phosphors appeared resulting from the substitution of the Si4+ ion with Zn2+ of tetrahedral sites in the phosphors. A PL spectrum at 6 K showed two dominant peaks which appeared at 375 and 400 nm. The results of the PL measurements showed that the intensity of the Si-doped ZnGa2O4 phosphor was enhanced in comparison with that of the undoped ZnGa2O4 phosphors and that the emission peak position shifted to the longer wavelength by doping the Si into the ZnGa2O4. The intensity ratio between the peaks at 375 and 400 nm decreased below a Si mole fraction of 0.02, and it increased above the Si mole fraction of 0.02. This behavior has been explained by introducing the band model utilizing the acceptor level of the zinc vacancy and the donor level of the Si4+ dopant.