Luminescence of Bi4 Ge3 O12 : Spectral and decay properties

Intense broadband emission in the visible is observed from crystals of Bi₄Ge₃O₁₂ under optical and x‐ray excitation. From measurements of absorption, reflection, fluorescence, and excitation spectra, the emission is assigned to ³P₁ → ¹S₀ transitions of Bi³⁺. The Stokes shift is large, $\text{[inverted lazy s]14 000\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ . The temperature dependences of the fluorescence intensity and lifetime in the range 77–400 °K establish that nonradiative decay becomes significant at temperatures ⪞250°K. Comparison of the properties of Bi₄Ge₃O₁₂ with those of Bi₁₂GeO₂₀ and other bismuth‐activated materials demonstrates the importance of the Stokes shift and the ¹S‐³P energy difference in determining the luminescence behavior. The use of Bi₄Ge₃O₁₂ as a laser host crystal for rare‐earth and iron group activator ions, and as a scintillator material is discussed briefly.