Phosphorescence

Definition

Phosphorescence is the phenomenon where a substance absorbs energy and then re-emits it as light over an extended period. This process involves the excitation of electrons to a higher energy state, followed by a slow transition back to their original state, resulting in a glow that can last from seconds to hours after the initial energy source is removed. It is different from fluorescence, where the light emission occurs almost instantaneously after excitation.

5 Must Know Facts For Your Next Test

1. Phosphorescence occurs in materials that can trap excited electrons for longer periods, allowing them to release energy slowly as visible light.
2. Common examples of phosphorescent materials include glow-in-the-dark stickers and certain types of paints that continue to emit light after being exposed to a light source.
3. The phenomenon relies on specific electronic transitions known as 'forbidden transitions' that are less likely but can occur over longer time scales.
4. The effectiveness of phosphorescence can be influenced by factors such as temperature and the chemical composition of the phosphorescent material.
5. Unlike fluorescence, which typically ceases immediately when the light source is removed, phosphorescent materials can glow for several minutes or even hours.

Review Questions

• How does phosphorescence differ from fluorescence in terms of energy absorption and light emission?
  • Phosphorescence differs from fluorescence primarily in the duration and mechanism of light emission. In fluorescence, the absorbed energy is released almost instantly, within nanoseconds, as light when the energy source is still present. In contrast, phosphorescence involves a delayed emission process where absorbed energy is released slowly over time, allowing the material to continue glowing even after the energy source is removed. This difference is due to the presence of 'forbidden transitions' in phosphorescent materials, which extend the duration of emitted light.
• What role do electronic transitions play in the process of phosphorescence?
  • Electronic transitions are crucial in phosphorescence because they determine how energy is absorbed and subsequently emitted as light. When a phosphorescent material absorbs energy, electrons are excited to a higher energy state. The unique aspect of phosphorescence is that some of these excited electrons undergo 'forbidden transitions' that allow them to remain trapped in an excited state longer than normal before returning to their ground state. This delayed return causes the prolonged glow characteristic of phosphorescent materials after the initial excitation source has been removed.
• Evaluate how environmental factors like temperature might affect the phosphorescent properties of a material.
  • Environmental factors such as temperature significantly influence the phosphorescent properties of materials by impacting both the excitation process and the rate at which trapped electrons return to their ground state. Higher temperatures can provide additional energy to excited electrons, potentially causing them to transition back more quickly, thus shortening the duration of phosphorescence. Conversely, lower temperatures might stabilize trapped electrons and prolong their excited state, resulting in a longer-lasting glow. Understanding these interactions helps in designing better phosphorescent materials for applications that require prolonged illumination.

Related terms

Fluorescence:

A process where a substance absorbs light or other electromagnetic radiation and then re-emits it almost instantly, typically within nanoseconds.

Excited State: A higher energy state of an atom or molecule when electrons are energized and elevated to a level above their ground state.

Afterglow: The continued emission of light by a phosphorescent material after the initial excitation source has been removed.