Electroluminescent devices are devices that convert electrical energy into light. This process occurs through a phenomenon called electroluminescence, where the material emits light in response to an electric current passing through it. The exact mechanism can vary depending on the type of electroluminescent device, but the basic principle remains the same.
There are two common types of electroluminescent devices: inorganic electroluminescent devices (such as LED - Light Emitting Diodes) and organic electroluminescent devices (such as OLED - Organic Light Emitting Diodes).
Inorganic Electroluminescent Devices (LEDs):
In LEDs, the electroluminescence phenomenon occurs in a semiconductor material. The semiconductor is typically made of a compound such as gallium arsenide (GaAs) or gallium nitride (GaN) doped with impurities to create a P-N junction.
When a voltage is applied across the P-N junction (forward bias), electrons and holes are injected into the semiconductor material. Electrons are negatively charged particles, and holes are positively charged locations where electrons are missing. When an electron combines with a hole, it falls to a lower energy state, releasing energy in the form of photons (light). The energy of the emitted photons depends on the bandgap of the semiconductor material.
The semiconductor's properties and the energy band structure determine the color of the emitted light. For instance, different combinations of materials and doping can produce red, green, blue, or other colors of light. This process allows LEDs to emit light efficiently and in a wide range of colors.
Organic Electroluminescent Devices (OLEDs):
OLEDs use organic (carbon-based) materials that can emit light when an electric current is applied. Unlike LEDs, OLEDs do not require a separate P-N junction. Instead, they typically consist of multiple organic layers sandwiched between two electrodes, an anode (positively charged) and a cathode (negatively charged).
The organic layers in an OLED device include an emissive layer, which is responsible for emitting light. When a voltage is applied between the anode and the cathode, electrons and holes are injected into the emissive layer. As electrons and holes combine within the emissive layer, they form excited states, and as these excited states relax back to their ground states, light is emitted.
The advantage of OLEDs is that they can be made flexible and even transparent, enabling various applications such as OLED displays in TVs, smartphones, and lighting panels.
In both types of electroluminescent devices, the conversion of electrical energy into light is highly efficient, making them popular choices for various lighting and display applications.