Phosphor: A Material that Emits Light When Struck by Electrons

August 31, 2024 3 min read Science and Technology Materials Science Phosphor CRT Screens Luminescent Material Cathode-Ray Tube Electronics

Phosphor is a material commonly used on the inside surface of CRT screens, which emits light when hit by electrons, enabling the display of images and text on the screen.

On this page

Phosphor is a luminescent material that emits light when it is excited by electrons. This excitation causes the phosphor to glow, which makes it valuable in various display technologies, most notably in cathode-ray tube (CRT) screens used in older television sets and computer monitors.

Definition and Properties

Phosphor is a solid material that can emit visible light through a process known as luminescence. When energized particles such as electrons or ultraviolet (UV) photons strike the phosphor, it absorbs the energy and later releases it in the form of light. This phenomenon is known as fluorescence when the light emission ceases immediately after excitation stops, and phosphorescence when the light persists for some time after excitation.

Types of Phosphor

Phosphors can be categorized based on their emission properties and structural characteristics:

Fluorescent Phosphors: Emit light only while being excited by energy.
Phosphorescent Phosphors: Continue to emit light after the excitation energy source is removed.
Cathodoluminescent Phosphors: Specifically designed to emit light when struck by electrons, commonly used in CRT screens.
Photoluminescent Phosphors: Emit light in response to UV light exposure.

Common Examples and Uses

Zinc Sulfide (ZnS:Cu): Used in old CRT screens for its strong green emission.
Yttrium Aluminium Garnet (YAG:Ce): Used in white LEDs for its excellent light-emitting properties.

Historical Context

The use of phosphor dates back to the development of the CRT in the early 20th century. Pioneers like Karl Ferdinand Braun and later inventors adapted phosphor materials to create visible displays essential for early television and radar technology.

Special Considerations

Efficiency: The efficiency of a phosphor material determines how much of the absorbed energy is converted into visible light.
Lifespan: Long-term use might degrade phosphors, reducing brightness over time.
Color: By combining different phosphors, manufacturers can create displays capable of producing a wide range of colors.

Applicability in Modern Technology

While CRT technology has largely been replaced by flat-panel displays such as LCDs and OLEDs, phosphors are still vital in modern applications such as:

LED screens: Utilizing phosphor coatings to convert blue LED light to white light.
Medical Imaging: Phosphor screens used in X-ray imaging.
Lighting: Energy-efficient fluorescent lamps and white LEDs.

Fluorescence: Immediate light emission upon excitation.
Phosphorescence: Sustained light emission after the excitation source is removed.
Cathodoluminescence: Light emission due to electron impact, used explicitly in CRTs.

FAQs

Is phosphor harmful to health?

In most commercially-used forms, phosphor compounds are not dangerously toxic. However, certain components can be harmful if ingested or inhaled in large quantities.

What replaced phosphor in modern screens?

Modern screens often use organic light-emitting diodes (OLEDs) and liquid crystal displays (LCDs) which do not rely on traditional phosphors.

Why are different colors of phosphor used in CRTs?

Different colors are utilized to produce a full spectrum of colors in the display, enhancing image quality and color reproduction.

References

Wikipedia Contributors. “Phosphor.” Wikipedia, The Free Encyclopedia, Wikipedia, Last visited August 2024.
Ashcroft, N.W., Mermin, N.D. (1976). Solid State Physics. Cengage Learning.

Summary

Phosphor materials play a critical role in the visualization technology of the 20th century, particularly in CRT screens. They emit light when struck by electrons, enabling the display of images and text. Though largely supplanted by newer technologies today, phosphors continue to be relevant in specific applications such as medical imaging and modern lighting solutions.