Controllable ultra-broadband visible and near-infrared photoemissions in Bi-doped germanium-borate glasses

The design of functional materials with tunable broadband luminescence performance is still of great interest in the fields of lighting, solar cells, tunable lasers, and optical amplifiers. Here, via a melt-quenching method, a series of bismuth (Bi)-doped germanium-borate glasses with composition of 40GeO₂–25B₂O₃–25Gd₂O₃–10La₂O₃–xBi₂O₃ have been prepared, in which multiple Bi active centers can be stabilized simultaneously. Dual-modulating modes of visible (380-750 nm) and near-infrared (NIR) (1000-1600 nm) broadband photoemissions were effectively controlled under flexible excitation scheme. Photoluminescence (PL) spectra at low temperature 10-298 K were appropriately employed to interpret such an unusual wide visible emission band. To further illustrate the origin of NIR component, transmission electron microscopy (TEM) measurement was carried out. It is demonstrated experimentally that the visible emission mainly originates from the collective contribution of the ³P₁/³P₀¹S₀ transitions of Bi³⁺, while the broadband NIR luminescence should be related to the formation of low valent Bi⁺ and (or) Bi⁰ centers. This work may help to enhance the knowledge of the complex luminescence mechanism for the Bi species and it also enables such transparent glass materials to be a promising candidate for the multifunctional tunable light source.