EL Phosphor

EL Phosphor Technology

 

EL (electroluminescent) phosphors are inorganic materials that directly convert electricity to light. They are widely used in EL wires and EL panels and can be applied to glass or flexible plastic and powered by either DC or AC drivers. EL phosphor panels can be manufactured into a wide range of colors including blue, cyan, green, orange, white, red, and even the infrared. EL phosphor panel fabrication techniques include screen printing, spray painting, and sputtering. The most common EL phosphors are based on copper-doped and manganese-doped zinc sulfide (ZnS:Cu and ZnS:Mn).

Although LEDs (light-emitting diodes) and OLEDs (organic light-emitting diodes) are also considered electroluminescent devices, they function somehow differently from EL phosphor lamps. LEDs and OLEDs are built using PN junctions formed between semiconductors where electrons and holes combine at the junction boundary. In an EL lamp, electrons are driven across the phosphor layer by a high electric filed causing the entire layer to become active and emit light. LEDs and OLEDs are generally direct-current (DC) devices while EL phosphor panels can be driven at either DC or AC (alternating current).

 

Powder EL

Most commercial EL panels are made using powder EL phosphors by screen printing an EL ink on a conducting substrate coated with a dielectric layer. A transparent conductor on glass or plastic is then used for applying a high electric field across the EL structure producing light, which is then extracted from one side. The transparent substrate is generally coated with a conducting indium tin oxide film (ITO).

 

Thin-film EL

Other less common types of EL panels often referred to as TFEL (Thin-Film Electroluminescent) structures are also possible. TFELs are made using thin-film phosphor layers deposited by evaporation or sputtering on ITO glass at high temperatures. The dielectric layers and metal conducting layers (typically aluminum) are also evaporated and deposited at high temperatures.