Fig. 2. Structure characterizations of La₄GeO₈:Bi³⁺ phosphor and its defect formation.

a X-ray powder diffraction (XRD) patterns of the LGO matrix with the measured data, fitted data, difference, and Bragg position, which are based on the Rietveld refinement. b The projected electronic density of states (PDOS) of the LGO matrix, which is obtained via DFT calculations. c The crystal structure of LGO from the b-axis direction and the polyhedral structure of La1–La3, where the green, red and blue spheres represent Ge, O, and La atoms, respectively. d The La–O bond length, which is obtained via DFT calculations. e Raman spectra of LGO:xBi³⁺ (x = 0, 0.007). f XPS analysis of the O 1s orbital for the La₄GeO₈ matrix (LGO) and La_3.993GeO₈:0.007Bi³⁺ (LGO:Bi³⁺)