Fluorescent

Definition

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a type of luminescence where the substance absorbs energy, typically in the form of ultraviolet or visible light, and then re-emits the energy as visible light. This process occurs due to the electronic structure of the fluorescent material and is a fundamental concept in the understanding of color and color vision.

5 Must Know Facts For Your Next Test

1. Fluorescent materials absorb energy in the form of ultraviolet or visible light and then re-emit that energy as visible light, resulting in the characteristic glow or color of the material.
2. The Stokes shift, the difference in wavelength between the absorbed and emitted light, is a key characteristic of fluorescent materials and is responsible for the shift in color observed.
3. Fluorescent materials are used in a variety of applications, including fluorescent lighting, glow-in-the-dark products, and as markers in biological and medical research.
4. The efficiency of a fluorescent material is determined by its quantum yield, which is the ratio of the number of photons emitted to the number of photons absorbed.
5. The specific color emitted by a fluorescent material is determined by the electronic structure and composition of the material, which affects the energy levels of the electrons and the resulting wavelength of the emitted light.

Review Questions

• Explain the process of fluorescence and how it differs from other forms of luminescence.
  • Fluorescence is a type of luminescence where a material absorbs energy, typically in the form of ultraviolet or visible light, and then re-emits that energy as visible light. This process occurs due to the electronic structure of the fluorescent material, where electrons are excited to higher energy levels and then return to their ground state, releasing the energy as a photon of visible light. Unlike phosphorescence, where the emission of light continues for a noticeable period after the excitation source has been removed, fluorescence stops immediately once the excitation source is removed.
• Describe the role of the Stokes shift in the characteristics of fluorescent materials.
  • The Stokes shift is the difference in wavelength between the absorbed and emitted light in a fluorescent material. This shift is a key characteristic of fluorescent materials and is responsible for the observed change in color between the absorbed and emitted light. The Stokes shift occurs because the emitted light has a lower energy than the absorbed light, as some of the energy is lost through various relaxation processes within the material. The specific Stokes shift of a fluorescent material determines its color and is influenced by the electronic structure and composition of the material.
• Analyze the factors that influence the efficiency and applications of fluorescent materials.
  • The efficiency of a fluorescent material is determined by its quantum yield, which is the ratio of the number of photons emitted to the number of photons absorbed. Factors such as the electronic structure, composition, and environmental conditions (e.g., temperature, pH) can all affect the quantum yield and, consequently, the efficiency of the fluorescent material. Highly efficient fluorescent materials are used in a variety of applications, including fluorescent lighting, glow-in-the-dark products, and as markers in biological and medical research, where their ability to absorb and re-emit light is crucial for their functionality. The specific color emitted by a fluorescent material is also an important factor in its applications, as it determines the appearance and visibility of the material.

Related terms

Luminescence: The emission of light by a substance that is not due to the substance's temperature, but rather due to a chemical or physical change in the material.

Phosphorescence:

A type of luminescence where the emission of light continues for a noticeable period after the excitation source has been removed, unlike fluorescence which stops immediately.

Stokes Shift: The difference in wavelength between the absorbed and emitted light in a fluorescent or phosphorescent material, where the emitted light is of longer wavelength (lower energy) than the absorbed light.