The Eu2+-doped G-La2Si2O7 phosphor was successfully prepared through the high-temperature solid-state reaction method with the aid of AlF3 flux. The results of Eu L3-edge XANES characterization showed that only Eu3+ can be detected in as-received G-La2Si2O7 phosphor and that Al2O3 addition leads to a partial reduction of Eu3+ to Eu2+, while complete reduction occurs with AlF3 addition. The obtained Eu2+-doped G-La2Si2O7 phosphor exhibited typical Eu2+ blue-green emission under the near-UV light excitation. The analysis of Fourier transform infrared spectroscopy (FT-IR) and 27Al nuclear magnetic resonance (NMR) results suggests that Al occupies the Si sites and F occupies the O sites. The positive influence of Al–F doping is related to the structure of the produced phosphors, which was analyzed with the aid of first-principles density functional calculations. The results of the theoretical calculations are a good match to the experimental findings.