

Origin of Emission and Absorption Process
In the mid 19th century, scientists found that, when the materials are heated in flames or kept in electrical discharge, the lights are emitted with well-defined frequencies. The study of emission and absorption spectra of atoms plays a predominant role in developing the atomic structure. Many attempted and failed to describe the origin of the emission and absorption process of light with a simple atom and hydrogen framework using electromagnetism and mechanics.
Bohr’s Atom Model
In 1913, A Danish physicist, Neil Bohr proposed the hydrogen atom model. It explains the structure of atoms, especially the hydrogen atom. The electrons orbiting around the nucleus in the atom allowed certain stationary states with well-defined energies. When an electron transits from one state to another, the atom can absorb or emit photons. The energy conserved during this process is determined by the frequency of the light emitted or absorbed. The entire process depends on the emission and absorption process of light.
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When the electrons are excited and returning from the higher energy state to the lower energy state, the light with certain frequencies will get emitted.
Spontaneous Emission
Spontaneous emission is the process of a quantum mechanical system, which transits electrons from an excited state to a lower energy state and emits a quantized amount of energy in the form of a photon.
If the isolated atom is excited from the lower energy state to the higher energy state, the atom will remain the same for a short period, before emitting a photon. On average, when the atom excites, the average time for the spontaneous emission of photons will stay in the order of 10−9 to 10−8 seconds.
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The electrons in an excited state will automatically reach the lower state during spontaneous emission. Stimulated emission requires some external energy to stimulate it back to lower energy levels.
Stimulated Emission
In the stimulated emission, the photons with certain energy will trigger an atom in an excited state to emit a photon to transit to a lower energy state.
According to the intensity of the light falling on the atom, the atom will absorb a photon and excites, this process is known as a probabilistic event. Even without knowing the principle behind stimulated emission, Einstein in 1917, presented the thermodynamic arguments, which contains three types of radioactive transitions in an atom-stimulated emission. Here, the energy released during the stimulated emission is directly proportional to the intensity of the light intense atom.
Einstein expressed that the three possible radiative transition routes depend on emission and absorption processes, They are also called Einstein coefficients. They are
Spontaneous emission
Stimulated Emission
Absorption
According to Einstein’s stimulated emission process, the energy of the emitted photon is equivalent to the stimulating photons. The energies get polarized in the same direction, in phase with photons. After 40 years of working with Stimulated emission, Einstein invented the LASER (Light Amplification by Stimulated Emission of Radiation). The laser lights will work on the property of stimulated emissions. The Laser lights are highly monochromatic, directional, and coherent.
Spectroscopy
Spectroscopy is the specific study of colours from the visible range of the electromagnetic spectrum. The study of emission and absorption of lights is known as spectroscopy.
Applications of Spectroscopy
We are using spectroscopy in our day-to-day life in various fields. Some of the applications include:
To determine the atomic structure of the samples
You can find the oxygen content in the marine and freshwater
Can analyze the metabolic structure of muscles
Can be used as a respiratory gas analysis in the medical field
Can use spectroscopy to improve efficiency through altering the structure of drugs
Quantum Electrodynamics
In the late 1920s and 1930s Paul Dirac, Pascual Jordan, Werner Heisenberg, Wolfgang Pauli, and others laid the foundation of the quantum mechanical theory of light. Richard Feynman, Tomonaga Shinichiro, and Julian S Schwinger together completely developed the theory of quantum electrodynamics. Quantum Electrodynamics explains the interactions of electromagnetic radiations with charged particles and among the charged particles. In Quantum Electrodynamics, the photons will act as carriers of electric and magnetic forces. For eg, the two identical charged particles will electrically repel each other because of interchanging the virtual photons. It is impossible to measure the virtual photons directly. The existence of virtual photons will violate the conservation laws of energy and momentum. Here, every charged particle will emit the photons when it detects the light.
Though the mathematical complexity of QED is not proven, the QED’s are theoretically proven through experiments. So, this is considered the prototype field theory of physics.
The theoretical framework of the QED has involved the process of transformation of photons into matter and matter into a photon. During the creation of pairs, the photons will enter an atomic nucleus and it will disappear, Further, its energy will be converted into electrons and positrons. During the pair annihilation, the electron-positron pair will disappear and high-energy photons are created. These processes are known as the central importance of cosmology, which explains that light is a primary component of the universe!!
FAQs on Emission and Absorption of Light
1. What is meant by emission and absorption of light in atomic physics?
Emission of light occurs when an atom’s electron moves from a higher energy level to a lower one, releasing a photon. Absorption of light happens when an electron absorbs a photon and jumps to a higher energy level. Both processes are fundamental to understanding atomic structure as per CBSE 2025–26 Physics syllabus.
2. How do emission and absorption spectra differ, and why are these important in spectroscopy?
Emission spectra consist of bright lines at specific wavelengths visible when electrons return to lower energy states and emit photons. Absorption spectra show dark lines where specific wavelengths are absorbed by electrons transitioning to higher energy states. These spectra help identify elements and are vital in spectroscopy applications.
3. Explain the significance of Bohr’s atomic model in understanding emission and absorption of light.
Bohr’s model introduced the concept of discrete energy levels for electrons in atoms. It explains that light is emitted or absorbed only when electrons change energy levels, leading to quantised emission or absorption spectra. This model laid the foundation for modern quantum mechanics and spectroscopy.
4. What are the main applications of emission and absorption of light in real life?
Applications include:
- Determining atomic structure in laboratories
- Measuring oxygen content in water bodies
- Analysing metabolic processes in muscles
- Respiratory gas analysis in medicine
- Pharmaceutical research using spectroscopy for drug structuring
5. What is spontaneous emission and how is it different from stimulated emission?
Spontaneous emission occurs naturally when an excited electron drops to a lower energy state and releases a photon without external influence. Stimulated emission happens when an incoming photon forces an excited electron to emit another photon of identical energy, as used in LASER technology. Stimulated emission is the working principle behind lasers.
6. Why are the energy levels in an atom described as quantised, and what role does this play in light emission or absorption?
Energy levels in an atom are quantised, meaning electrons can only occupy specific energy states. When electrons move between these states, only certain photon energies (specific frequencies of light) can be emitted or absorbed. This is why emission and absorption spectra are made up of discrete lines.
7. How did quantum electrodynamics (QED) expand our understanding of light interactions at the atomic level?
Quantum electrodynamics (QED) describes how photons (light particles) interact with charged particles like electrons. QED explains processes like virtual photon exchange and the creation/annihilation of electron-positron pairs, fundamentally deepening our understanding of light’s role in atomic and subatomic processes.
8. In what ways are emission and absorption spectra used for chemical and astronomical analysis?
Spectra are used to identify elements in a substance by their unique spectral lines and to determine chemical compositions of distant stars and planets. This ability is crucial for chemical analysis and astronomical studies, making these processes fundamental tools in science.
9. What misconceptions might students have about emission and absorption of light, and how can they avoid them?
A common misconception is that electrons can absorb or emit any amount of energy. In reality, only photons matching the exact energy difference between quantised levels can be absorbed or emitted. To avoid confusion, remember that each element has unique, fixed energy transitions reflected in its spectra.
10. How does the intensity of light influence the process of absorption at the atomic level?
The probability of an atom absorbing light increases with intensity, because a stronger light source provides more photons. However, the energy of photons (frequency) still needs to exactly match the energy gap between electron states for absorption to occur.

















