The duration of phosphorescence exhibited by a phosphor is known as ______.
persistence
Understanding Phosphorescence and its Duration
The question asks about the specific term used to describe how long the light emission from a phosphor lasts after the exciting energy source is removed. This phenomenon, where light continues to be emitted for a noticeable period after excitation, is known as phosphorescence.
What is Phosphorescence?
Phosphorescence is a type of photoluminescence. It's similar to fluorescence, but with a key difference: the emitted light continues for some time after the excitation source is turned off. This happens because the excited electrons in the phosphor material get trapped in intermediate energy levels and then slowly release energy as light over time. This slow release causes the glow to persist.
The Term for Duration
The duration for which a phosphor continues to emit light after the excitation source is removed is a specific property. Let's look at the options provided:
- Fluorescence: This is a type of luminescence where light emission stops almost immediately (within nanoseconds) after the excitation source is removed. It does not describe the duration of light emission, especially for phosphorescence.
- Persistence: This term specifically refers to the length of time that the luminescence of a material, such as a phosphor, continues after the excitation source is removed. It directly measures how long the glow "persists".
- Phosphorescence: This is the name of the luminescence phenomenon itself, not the duration of the phenomenon.
- Deflection: This term is unrelated to light emission or luminescence properties. It typically refers to the bending or changing direction of something, like a beam of light or electrons.
Based on the definitions, the term that describes the duration of phosphorescence exhibited by a phosphor is persistence.
Why Persistence is the Correct Term
Persistence quantifies the characteristic glow time of phosphors. Different phosphors have different persistence levels, ranging from very short (milliseconds) to very long (hours). This property is crucial for applications like cathode ray tubes (CRTs), where the screen needs to glow long enough for an image to be perceived by the human eye without excessive flicker.
Conclusion
The duration of phosphorescence exhibited by a phosphor is known as persistence.
| Term | Description |
|---|---|
| Fluorescence | Light emission stops almost immediately after excitation. |
| Phosphorescence | Light emission continues for a noticeable time after excitation stops. |
| Persistence | The duration for which luminescence (like phosphorescence) continues after excitation stops. |
| Deflection | Changing direction; unrelated to luminescence duration. |
Revision Table: Key Luminescence Terms
| Term | Definition | Duration After Excitation Stops |
|---|---|---|
| Luminescence | Emission of light by a substance not resulting from heat; includes fluorescence and phosphorescence. | Varies |
| Fluorescence | A type of photoluminescence. | Very short (nanoseconds to microseconds) |
| Phosphorescence | A type of photoluminescence. | Noticeable duration (milliseconds to hours or days) |
| Phosphor | A substance that exhibits luminescence when exposed to radiation (like light, electron beams). | N/A (It's the material, not a process or duration) |
| Persistence | The duration of luminescence after the excitation source is removed. | Measures the time duration |
Additional Information on Phosphor Persistence
The persistence of a phosphor depends on the specific material's energy band structure and the presence of traps for excited electrons. Deep traps lead to longer persistence, as electrons take longer to de-excite and release photons. Persistence is a key specification for phosphors used in displays, safety signs (glow-in-the-dark), and other applications where a lingering glow is desired or necessary.
Important Questions from Graphics Systems
If we want to resize a 1024 × 768 pixels image to one that is 640 pixels wide with the same aspect ratio, what would be the height of the resized image?
Consider a raster system with resolution 640 by 480. What size is frame buffer (in bytes) for this system to store 12 bits per pixel?
A graphic display system has a frame buffer that is 640 pixels wide, 480 pixels high and 1 bit of color depth. If the access time for each pixel on the average is 200 nanoseconds, then the refresh rate of this frame buffer is approximately:
Which component of CRT regulate the intensity of electron beam?
- Which of the following are applicable to programming graphics (pre-design phase) during design development process?
(a) Graphic worksheets
(b) Analysis cards
(c) Variety of matrics
(d) Bubble diagram
Choose the correct option :
