Views:211 Author:Site Editor Publish Time: 2020-04-06 Origin:Site
long-lasting luminous material is referred to as long afterglow material, which is a photoluminous material. It is a kind of material that absorbs energy and can continue to emit light after the excitation stops. It is a material with promising applications.
After the long afterglow material is excited, it can continue to emit light for a long time. The key is to have a trap energy state of an appropriate depth, that is, an energy storage. The free electrons generated during photoexcitation fall into the trap and are stored. After the excitation stops, the trapped electrons or trap holes are released by the thermal disturbance at normal temperature, and the afterglow is compounded with the luminous center. As the trap was gradually emptied, the afterglow gradually faded to disappear. The trap state originates from the structural defect of the crystal. In other words, seeking the best crystal defects to form the best traps is the main factor in obtaining long afterglow. The length of the afterglow time depends on the depth of the trap and the intensity of the afterglow. The intensity of the afterglow light depends on the trap concentration, capacity, and rate of electron release. The crystal defects are mainly caused by impurities, in addition to the structural defects naturally formed during the material preparation process.
The long afterglow luminous mechanism is actually a process of how energy is transmitted between the luminous center and the defect center. Specific long afterglow materials have different luminous models. Two common types are described below.
For this type of material, the earliest model was the hole transport model proposed by Matsuzawa et al in the SrAl2O4: Eu2 +, Dy3 + system. Based on this model, Matsuzawa believes that in the long afterglow materials SrAl2O4: Eu2 +, Dy3 +, Eu is the electron capture center and Dy is the hole capture center. When the material is excited by UV, Eu2 + can trap electrons and become Eu +. The resulting holes are trapped by Dy3 + to generate Dy4 +. After the excitation stops, the holes escape due to the thermal movement. The process with the characteristics that cause Eu to glow. This model is widely cited in the mechanism explanation of various Eu and Dy co-doped long afterglow materials, and has become a general explanation of the mechanism of Eu and Dy co-doped long afterglow materials.
The displacement coordinate model was first proposed by Qiu Jianrong and Su Shi. FIG. 3 is a schematic diagram of a displacement coordinate model. A is the ground state energy level of Eu2 +, B is its excited state energy level, and C is the defect energy level. C can be a doped impurity ion or a defect energy level caused by some defects in the matrix. Su Yan and others believe that C can play a role in capturing electrons. Under the action of an external light source, the electrons are excited to transition from the ground state to the excited state (1), and some electrons transition to the low energy state to emit light (2). The other 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 again to return to the excited state energy level, transitions to the ground state and emits light. The length of afterglow is related to the number of electrons stored in the defect energy level and the absorbed energy (heat). The more electrons in the defect energy level, the longer the afterglow time, the more absorbed energy, and thus continuous light emission.
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