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, inverted lazy s14 000 cm−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.