Hole transport model
For this type of material, the earliest model was the hole transport model proposed by Matsuzawa et al. in the SrAl2O4:Eu, Dy system. Based on this model, Matsuzawa believes that in the long afterglow materials SrAl2O4:Eu, Dy, Eu is the electron capture center and Dy is the hole trapping center. When the material is excited by UV, Eu can capture electrons to become Eu, and the resulting holes are captured by Dy through the valence band to generate Dy. After the excitation is stopped, the holes escape due to the thermal motion, and the opposite is true. The process and the luminescence that lead to Eu are shown in Figure 3. This model is widely cited in the explanation of the mechanism of various Eu and Dy co-doped long afterglow materials, and becomes a general explanation for the mechanism of long afterglow materials co-doped by Eu and Dy.
2 displacement coordinate model
The displacement coordinate model was first proposed by Qiu Jianrong and Su Shi. Figure 3 is a schematic diagram of the displacement coordinate model. A is the ground state energy level of Eu2+, B is its excited state energy level, and C energy level is the defect energy level. C may be an impurity ion incorporated or a defect level generated by certain defects in the matrix. Su Shi and others believe that C can play the role of capturing electrons. Under the action of an external light source, electrons are excited to transition from the ground state to the excited state (1), and a portion of the electrons transition back to low-energy luminescence (2). Another part of the electrons is stored in the defect energy and C through the relaxation process (3). When the defect level electron absorbs energy, it is excited back to the excited state level, and transitions back to the ground state to emit light. The length of the afterglow is related to the amount of electrons stored in the defect level and the absorbed energy (heat). The more electrons in the defect level, the longer the afterglow time and the more energy absorbed, resulting in continuous illumination.