Multi-band near-infrared emission in low concentration bismuth doped alkaline earth alumino-boro-germanate glass

Ultra-broadband near-infrared emission mainly consisting of three bands around 940 nm, 1180 nm and 1500 nm was investigated under excitation at 460 nm in RO-Al2O3-B2O3-GeO2 (R = Mg, Ca, Sr and Ba) glasses with 0.005 mol% Bi2O3 doping. With the radius increasing of alkaline earth ion, the first and the third bands became stronger while the second one became weaker gradually, but their photoluminescence thermal stability and quantum yield declined gradually. The luminescence origination should be multi-type bismuth active centers (BACs). Furthermore, energy levels of the BAC assigning to the band around 1500 nm (BAC-1500) were analyzed through a contour plot of near-infrared emission intensity, excitation spectra and temperature dependent PL spectra. At last, the glass structure was studied by Raman and FT-IR spectra, molar volume and Vickers hardness. BAC-1500 should prefer the glass matrix with a looser framework, which indicates there was a competitive formation of different BACs in the glass.