Types of electroluminescence

Electroluminescence is also known as field luminescence. Electroluminescence is a kind of luminescence phenomenon in which electric energy is directly converted into light energy. It includes injection electroluminescence and intrinsic electroluminescence.
(1) Injection electroluminescence: electrons and holes are injected directly by the electrode mounted on the crystal. When the electrons and holes are recombined in the crystal, excess energy is released in the form of light. The basic structure of injection electroluminescence is junction diode (LED).
(2) Intrinsic electroluminescence: it can be divided into high-field electroluminescence and low-energy electroluminescence. High-field electroluminescence (HFEL) is the process in which the electrons in the phosphor or the electrons injected by the electrode accelerate inside the crystal under the effect of the external enhanced electric field, touch the luminescence center and make it excited or separated, and the electrons radiate luminescence when they return to the ground state.
From the point of view of luminescent materials, electroluminescence can be divided into non-electroluminescent and organic electroluminescent. Non-electroluminescent materials are generally equal-semiconductor materials. There are electroluminescent materials depending on the molecular weight of organic luminescent materials

It can be divided into small molecules and polymers. Small molecular OLED materials take organic dyes or pigments as luminescent materials, while polymer OLED materials take conjugated or non-conjugated polymers (polymers) as luminescent materials, and typical polymer luminescent materials are PPV and its derivatives.
Based on their different functions and device structures in OLED devices, electro-luminescent materials can also be classified into hole injection layer (HIL), hole transport layer (HTL), luminescent layer (EML), electron transport layer (ETL), electron injection layer (EIL) and other materials. Some of the luminescent materials have the function of cavity transport layer or electron transport layer. Such luminescent materials are also called as the main luminescent body. A small amount of doped organic fluorescence or phosphorescent dye in the luminescent material layer can accept the energy transfer of the autonomous luminescent and emit light of different colors via carriertrap mechanism. Such Dopant luminescent materials are also commonly known as passenger luminescent or Dopant luminescent, which is denoted by “Dopant” in English. From the perspective of luminescence principle, electroluminescence can be divided into high-field electroluminescence and low-field electroluminescence.
It can also be divided into thin film electroluminescent materials and dispersed electroluminescent materials.