Luminescence Principle of Light Storage and Self-illuminating Materials

Light storage and self-illuminating material is a material that can absorb and store light. After absorbing a few minutes of light, the material can shine in the dark for a long time.

 

Not all self-illuminating materials have luminescent properties. Only materials with structural defects and extrinsic defects in the crystal lattice of materials have the function of luminescence. The structural defects are holes and ions produced between lattice points, also known as lattice defects. Luminescence caused by lattice defects of materials is called self-activated luminescence. In the process of high temperature synthesis of self-illuminating materials, some element is added to the matrix material, and the ions of the added element are permeated into the matrix lattice to form impurity defects. The luminescence caused by this defect is called activated luminescence, and the elements added are called activators.

 

For photoluminescence materials, the energy of UV light of the excited materials can be absorbed by the matrix. After the matrix absorbs energy, the luminescence of the self-luminous material sign can be directly generated by the recombination of valence band electrons and holes, or by the luminescence center formed by lattice defects or impurity defects. This type of self-illuminating material is called composite self-luminous material. They are semiconductor-type compounds, and the matrix lattice is the medium that produces the luminescence process. When such self-illuminating materials are excited by UV light, the matrix absorbs energy first, and the energy is transferred to the luminescence center to produce luminescence. Therefore, in the process of absorbing energy, transferring energy and luminescence, the composite self-illuminating material has a large loss and low luminous efficiency.

 

When the UV light energy excites the material, it can also be absorbed directly by the luminescence center. after absorbing the energy, the electrons in the luminescence center transit from the low energy state to the high energy state, which produces luminescence when the electrons return from the high energy state to the low energy state. The material that luminescence only relates to the electronic transition in the luminescence center is characteristic self-illuminating material. The elements used as activators to form luminescence centers are mainly rare earth elements. The self-illuminating materials with oxygen compounds as the matrix, such as silicate, phosphate, aluminate and so on, all belong to the characteristic self-illuminating materials. The luminescence process of this kind of material is simpler than that of the composite material, its luminescence center directly absorbs the excitation energy, and the energy of the interaction between the luminescence center and the matrix is lower, which makes this kind of material have high luminescence efficiency.

The light storage material properties of sulfide series and aluminate series self-illuminating materials are related to the energy level of trap at different depths in these materials. When UV light excites, the energy level of trap with a certain energy depth captures enough electrons from the excited state and stores them. After UV light stops excitation, the electrons are stored, and gradually released under the thermal disturbance at room temperature, and the released electrons are then transferred to the excited state, which produces light when the electrons return from the excited state to the ground state.