Luminescence in nature refers to a phenomenon where substances transform energy obtained through certain forms into light radiation. Therefore, when luminous fibers are stimulated by external energy (such as light, applied electric fields, or electron beams), they can be excited by absorbing energy. During this process, some excess energy is released in the form of light and heat, and some chemical changes may also occur. Meanwhile, another part of the energy is released in the form of visible light, thus forming the luminescence of the fibers. The energy transfer in luminescent materials involves three processes: excitation, absorption, and conversion. After absorbing energy, the luminescent material, apart from emitting thermal radiation, can also store the external energy and continue to emit light for a period of time after the external energy stops stimulating it. This part of the light is called afterglow.
The luminescence mechanism of rare earth luminous fibers is related to the special electronic structure of the rare earth ions within the fibers. After absorbing external light, rare earth ions can transition from the ground state to the corresponding excited state through three types of transitions. The first is the interconfigurational fd transition; the second is the intraconfigurational ff transition; and the third is the charge transfer from the ligand to the rare earth ion. After being excited to the 4f” excited state through these three transitions, the subsequent radiation transition to a lower energy state can emit fluorescence.
The main luminescent centers of SrAL, O.Eu²+, Dy”+ phosphor fibers come from Eu²+ and Dy³+. Among them, Eu²+ plays a decisive role in the luminescence mechanism of the fibers. Eu²+ has two transition modes: f-d energy level absorption transition and f-f intra-configurational energy level transition. Due to the 5d orbital being exposed in the outer layer of the 4f5d electron configuration, it is relatively susceptible to external fields. The emission spectrum of the f-d energy level transition shows a broad band spectrum, and the emission intensity is also relatively high. By controlling the external electric field, the position of the 5d state can be changed, resulting in the luminescence region of Eu²+ easily falling at any position in the visible light region. Therefore, it is suitable for preparing long afterglow luminescent materials.