The key difference between photoionization and photoelectric emission is that photoionization refers to the interaction of electromagnetic radiation with matter, resulting in the dissociation of that matter into electrically charged particles, whereas photoelectric effect is a type of photoionization where ejection of electrons occurs when light shines on a surface of a material.
Photoionization is a physical process where an ion forms via the reaction between a photon and an atom or a molecule. Photoelectric effect is the process of emission of electrons when electromagnetic radiation hits a material.
CONTENTS
1. Overview and Key Difference
2. What is Photoionization
3. What is Photoelectric Emission
4. Photoionization vs Photoelectric Emission in Tabular Form
5. Summary – Photoionization and Photoelectric Emission
What is Photoionization?
Photoionization is a physical process where an ion forms via the reaction between a photon and an atom or a molecule. However, we cannot categorize all the interactions between photons and atoms or molecules as photoionization because some interactions form non-ionized species; therefore, we have to relate an interaction to the photoionization cross-section of the chemical species. Moreover, this photoionization cross-section depends on the energy of the photon and the properties of the chemical species undergoing the process.
Figure 01: Photoionization in Space
Multi-photon ionization is a type of photoionization where several photons combine their energies to ionize an atom or a molecule. Here, the energy of the photons should be below the threshold of ionization energy.
In addition to the above type, tunnel ionization is another type of photoionization reaction where the laser intensity used for the photoionization process is increased, or a longer wavelength is used, allowing a multi-photon ionization to take place. The result of this process is the distortion of the atomic potential in such a way that only a relatively low and narrow barrier between a bound state and the continuum state remains. Here, the electrons can tunnel through the barrier. These are called tunnel ionization and over the barrier ionization, respectively.
What is Photoelectric Emission?
The photoelectric effect is the emission of electrons when electromagnetic radiation hits a material. Electromagnetic radiation is usually light. The electrons that emit from this surface are known as photoelectrons. We can study this phenomenon in condensed matter physics and solid-state and quantum chemistry, as well. It is important to draw interferences about the properties of atoms, molecules, and solids.
Figure 02: Photoelectric Effect
Photoelectric emission is useful in electronic devices that are specialized for light detection and precisely timed electron emission. Typically, the emission of conduction electrons from typical metals tends to require a few electron Volt light quanta. This has to be corresponding to short-wavelength visible or UV light. But sometimes, emissions are induced with photons, which are approaching zero energy, similar to systems having negative electron affinity and the emission from excited states.
What is the Difference Between Photoionization and Photoelectric Emission?
Photoionization is a physical process where an ion forms via the reaction between a photon and an atom or a molecule. The photoelectric effect is the process of emission of electrons when electromagnetic radiation hits a material. The key difference between photoionization and photoelectric emission is that photoionization refers to the interaction of electromagnetic radiation with matter, resulting in the dissociation of that matter into electrically charged particles, whereas the photoelectric effect is a type of photoionization where ejection of electrons occurs when light shines on a surface of a material.
The following table summarizes the difference between photoionization and photoelectric emission.
Summary – Photoionization vs Photoelectric Emission
The photoelectric effect is the simplest type of photoionization. The key difference between photoionization and photoelectric emission is that photoionization refers to the interaction of electromagnetic radiation with matter, resulting in the dissociation of that matter into electrically charged particles, whereas the photoelectric effect is a type of photoionization where ejection of electrons occurs when light shines on a surface of a material.
Reference:
1. “Photo-Ionization.” Encyclopædia Britannica, Encyclopædia Britannica, Inc.
Image Courtesy:
1. “Hubble green filaments 20150402” By NASA, ESA, Galaxy Zoo Team and William Keel (University of Alabama, USA) – (Public Domain) via Commons Wikimedia
2. “Photoelectric effect in a solid – diagram” By Ponor – Own work (CC BY-SA 4.0) via Commons Wikimedia