Luminescence encompasses all processes by which atoms or molecules emit light. It doesn’t specify the intensity, colour, or source of the light. Examples include bioluminescence, chemiluminescence, and electroluminescence.
- Luminescence refers to any process where atoms or molecules emit light and encompasses a vast range of phenomena.
- Intensity Neutral: Luminescence doesn’t specify the brightness of the emitted light, whether it’s a faint glow or an intense beam.
- Colour Blind: Luminescence doesn’t tell us the colour of the emitted light, whether it’s blue, green, or a mixture of various wavelengths.
- Source Agnostic: The source of the light is not relevant for luminescence – it could be produced by a firefly, a light bulb, or a chemical reaction.
- Focus on Process: Luminescence is about the mechanism by which light is generated, regardless of the specifics of the light itself.
Mechanisms involved in luminescence
- Light Absorption and Emission: This mechanism, also known as photoexcitation, involves atoms absorbing light at specific wavelengths, which excites their electrons. Subsequently, the excited electrons “relax” by releasing this energy as light, often at different wavelengths and timescales. This principle underpins phenomena like phosphorescence, bioluminescence and fluorescent lights.
- Electromagnetic Interaction: This process, which accounts for the glow of neon signs, LEDs and display technologies, such as OLED, quantum dot, plasma and electro-luminescent displays, takes advantage of the interaction between atoms and electromagnetic fields, ultimately resulting in the emission of visible light. Applying an electric field directly to atoms excites electrons within a material’s structure. This energy boost enables electron transitions, leading to light emission.
- Electron transitions: An electron transition is the process by which an electron in an atom or molecule changes its energy level. This means it moves from one orbital (a region of probability where an electron is most likely found) to another, either closer to or further away from the nucleus.
- Thermal Excitation: This process utilizes heat to excite electrons within an atom. Elevated temperature imparts kinetic energy to electrons, promoting them to higher energy levels. Upon returning to their ground state, they release this excess energy in the form of light, as observed in incandescent bulbs and stellar bodies.
- Chemical Reactions: This mechanism, utilizes the energy released during chemical reactions to directly induce electron transitions. Specific reactions disrupt chemical bonds, releasing energy that excites electrons in participating molecules. These excited electrons then return to their ground state, emitting light, as seen in glow sticks and some bioluminescent organisms.
- Other mechanisms: Less common examples of luminescence mechanisms include:
- Sonoluminescence: light emission from collapsing bubbles
- Triboluminescence: light emission due to friction.
| Light Source | Description | Sub-atomic Process | Mechanism | Visible Light | Natural | Artificial |
|---|---|---|---|---|---|---|
| luminescence | Any process where atoms or molecules emit light. See Bioluminescence, Chemiluminescence, Electroluminescence, Fluorescence | Electron Excitation | Various mechanisms involving energy transitions in atoms/molecules | Varies (depends on mechanism) | Yes (some mechanisms) | Yes (various technologies) |
| Bioluminescence | A form of luminescence: Light emission by living organisms | Electron Excitation | Chemical reactions initiated and controlled by biological systems within living organisms. | Yes | Yes | Yes |
| Chemiluminescence | A form of luminescence: Light emission from chemical reactions | Electron Excitation | hemiluminescence relies solely on the chemical energy stored within the reacting molecules. | Varies (depends on reaction) | Yes (natural and synthetic) | Yes (glow sticks, analytical tools) |
| Electroluminescence | A form of luminescence:: Light emission due to electric fields | Electron Excitation | Applied electric field excites electrons in materials | Yes | No | Yes (LEDs, displays) |
| Fluorescence | A form of luminescence: Light emission from certain materials after absorbing light | Electron Excitation | Temporary absorption of light, followed by emission of a different (lower energy) color. | Yes | Yes (minerals and plants) | Yes (dyes, pigments, glow sticks) |
| Photoluminescence | ||||||
| Light emitting diode | A type of electroluminescence Semiconductor diode emitting light when current flows | Electron transition (recombination) | Recombination of electrons and holes in semiconductors releases energy as photons | Yes | No | Yes |
| Lasers (Light amplification by stimulated emission of radiation) | A type of photoluminescence | Light amplification by stimulated emission of radiation | Excited atoms/molecules release photons, stimulating further photon emission and amplifying light | Yes | No | Yes |
| Stellar light | Nuclear fusion | Fusion of hydrogen nuclei releases enormous energy, including light | Yes | Yes | No | |
| Fire | Chemiluminescence & Blackbody radiation | Hot objects emit light (incandescence), and chemical reactions create excited molecules (chemiluminescence) | Yes | Yes | Yes | |
| Lightning | Plasma processes | Hot, ionized gas (plasma) emits light through various mechanisms like recombination and Bremsstrahlung | Yes | Yes | No | |
| Neon signs | Gas discharge | Electric current excites gas atoms, which emit light upon returning to lower energy levels (similar to fluorescence) | Yes | No | Yes | |
| Light bulbs (Incandescent) | Blackbody radiation | Hot filament emits light due to thermal excitation of electrons | Yes | No | Yes | |
| Sunlamps | Ultraviolet radiation | Emit UV light, causing fluorescence in nearby materials | No (UV) | No | Yes |
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Summary