Plasma displays were very popular once before LED displays took over the market. Plasma displays are thin just like the LED ones and they can be tailor made into required sizes as big as the size of a blackboard. Plasma displays as the name suggests use something called as plasma for converting electric signals into visual images. The exact process of this conversion in itself is complicated and requires special attention. This article deals with the science behind the working of a plasma display. The questions like: “What exactly plasma is like?” and “How is it engineered to emit visible radiation?” are dealt here.
Plasma is formed when a solid or liquid or gas is taken and is subjected to extreme conditions like high temperature, high energy laser beams etc. As mentioned during our Physics tuition class, it is considered the fourth state of matter. When a certain amount of solid or liquid or gas is taken and subjected to extreme conditions the atoms or molecules in the species fall apart. Atoms lose electron/electrons and form ions; molecules can also break down into ions. The separation of neutral atom to charged species like ions and electrons gives plasma its bizarre nature. Plasma responds to magnetic or electric field and other stimuli like light in a very peculiar way.
In a typical plasma display there are cells containing noble gases and mercury vapour. These cells are placed in rows and columns and when a particular cell needs to be lit up energy is sent to it based on row-column address. When energy is fired, the gas instantaneously forms plasma. This plasma has fast moving ions and electrons. The fast moving electrons and ions collide with mercury atoms excite them. As a result mercury atoms release energy. The energy released is in the form of UV-radiation. Phosphor is painted on the inner side of these cells. Atoms present in the Phosphor system absorb UV radiation released from mercury atoms. The energy is absorbed by the electrons present in the phosphor system and as a result the electrons move to higher energy levels.
The excited electrons do not spend a lot of time at the higher energy level owing to the short half-life span of the excited state. The electrons jump back to lower energy levels, but while undergoing this process the final state of the electron is slightly higher than its initial energy state. Hence radiation of lower frequencies like visible and IR is emitted in the process. Thus plasma can be engineered to emit visible radiation under the influence of electric current.